; a ni dpi c :*ioal Series 7\LAEONTOLOG^ CAMBRIDGE BIOLOGICAL SERIES General Editor : — Arthur E. Shipley, M.A., F.R.S. FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE PALEONTOLOGY INVERTEBRATE CAMBRIDGE UNIVERSITY PRESS Uontom: FETTER LANE, E.C. C. F. CLAY, Manager Aft i' V I. t % i". i' 4 4* Si * * i * S GFtoinburgb : 100, PRINCES STREET ALSO HonUon: H. K. LEWIS, 136, GOWER STREET, W.C. Berlin: A. ASHER AND CO. ILnpjtg: F. A. BROCKHAUS $eto lorfe: G. P. PUTNAM'S SONS Bombag anU (Calcutta : MACMILLAN AND CO., Ltd. .4^ rights reserved J \D PALEONTOLOGY INVERTEBRATE by HENRY WOODS, M.A. University Lecturer in Palseozoology, Cambridge. FOURTH EDITION Cambridge . at the University Press 1909 First Edition 1893 Second Edition 1896 Third Edition 1902 Fourth Edition 1909 tf^-70 PREFACE TO FOURTH EDITION FT1HE general plan of this work is to give, in each group of the Invertebrata, first, a short account of its general zoological features with a more detailed descrip- tion of the hard parts of the animals ; secondly, its classification and the characters of the important genera, with remarks on the affinities of some forms ; and thirdly, a description of the present distribution, and the geo- logical range. The account of each genus is followed by the enumeration of one or more typical species, so as to guide the student in making use of a large collection. The illustrations are employed mainly for the purpose of explaining structure and terminology, and will not enable the student to dispense with the use of specimens. The list of palseontological works is intended to indicate where further information may be obtained in any branch of the subject ; it includes works of general interest in each group, and others dealing especially with British fossils. VI PREFACE TO FOURTH EDITION Some new figures have been added in this edition, and the work has been revised throughout. For advice and help in the parts dealing with the Echinoderma and the Polyzoa my thanks are due to Dr Bather and Mr W. D. Lang ; and for various suggestions I am indebted to Mr R. G. Carruthers, Mr G. C. Crick, Miss G. L. Elles, Dr G. J. Hinde, Dr F. L. Kitchin, Mr P. Lake and other friends. H. WOODS. May, 1909. CONTENTS List of Illustrations , . PAGE viii Divisions of the Stratified Rocks xii Introduction 1 Protozoa . 15 Porifera . 31 CCELENTERA 50 ECHINODERMA . 105 Annelida Brachiopoda 158 160 POLYZOA . 188 mollusca . Arthropoda 196 288 List of Pal.eontological Works . 355 Index 370 LIST OF ILLUSTRATIONS FIG. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. Sections of Foraminifera . Dimorphism of Nummulites Icevigatus .... Foraminifera. Biloculina. Miliolina. Spiroloculina. Textu laria. Lagena. Cristellaria. Nodosaria. Globigerina Rotalia ....... Nummulites ....... Heliosphcera ....... Radiolaria. Lithocampe. Trochodiscus. Podocyrtis Section of Leucosolenia ..... Section of Grantia . Sponge spicules Protospongia fenestrate,, Menevian Beds . Siplwnia tulipa, Upper Greensand . Obelia ........ Monograptus, Diplograptus .... Tetragraptus headi, Arenig Kocks . Eetiolites geinitzi, Silurian .... Diplograptus with reproductive sacs Didymograptus v-fractus. Early part of polypary Early stages of Monograptus and Diplograptus Diplograptus pristis ...... Phyllograptus , Arenig Rocks .... Stromatoporoidea. Sections of Actinostroma . Diagram of a simple coral .... Diagrammatic section of a Zoantharian polyp Diagrammatic section of a simple coral . Montlivaltia trochoides, Inferior Oolite . Budding of Dendrophyllia, Cyathophyllum, Gladochonus Section of Dissepiment of Galaxea . Section of septum and theca of Galaxea . Development of septa in Zaphrentis Section of Cyathophyllum murchisoni, Carboniferous Lithostrotion basaltiforme, Carboniferous PAGE 18 19 21 25 28 29 32 33 36 39 44 54 57 58 59 61 61 62 64 67 72 74 76 77 78 80 81 82 84 88 88 LIST OF ILLUSTRATIONS IX FIG. 32. Clisiophyllum Mpartitum, Carboniferous . 33. Cyclophyllum Jungites, Carboniferous 34. Sections of Zaphrentis delanouei, Carboniferous 35. Calceola sandalina, Devonian 36. Alcyonium digitatum, Recent ..... 37. Section of polyp of Alcyonium digitatum 38. Tubipora musica, Recent ...... 39. Heliopora ccerulea, Recent ..... 40. Heliolites porosus, Devonian ..... 41. Section of spine of Echinometra, and plate of Cidaris 42. Section of arm of Astropecten ..... 43. Diagram of the water-vascular system of a star-fish 44. Section of the arm of Ophioglypha .... 45. Ventral surface of Ophiura. Dorsal surface of Ophioglypha 46. A, Diagram of a regular echinoid. B, Apical disc of Echinus 47. Apical discs of Peltastes, Echinocorys, Collyrites, Palceechinus , Galerites .......... 48. Compound Ambulacral Plates. Pseudodiadema. Phymosoma 49. Spine and Plate of Cidaris florigemma 50. Under surface of Micraster cor-anguinum, Chalk 51. Melonechinus multiporus, Carboniferous . 52. Holaster subglobosus, Chalk .... 53. Micraster cor-bovis, Chalk .... 54. Anchor and plate of Synapta. Wheel of Chirodota 55. Botryocrinus decadactylus, Silurian 56. Actinocrinus triacontadactylus, Carboniferous. 57. Cyathocrinus longimanus, Silurian . 58. Apiocrinus parkinsoni, Bradford Clay 59. Glyptosphcera and Echinosphcera, Ordovician . 60. Lepadocrinus quadrifasciatus, Silurian . 61. Orophocrinus fusiformis, Carboniferous . 62. Pentremites godoni, Carboniferous . 63. Ambulacrum of Pentremites .... 64. Section of Pentremites sulcatus, Carboniferous 65. Section of ambulacrum of Pentremites 66. Section of ambulacrum of Codaster . 67. Section of ambulacrum of Phcenoschisma . 68. Edrioaster bigsbyi, Ordovician. 69. Magellania Jlavescens, Recent. Longitudinal section 70. Terebratula semiglobosa, Chalk 71. Cyrtia exporrecta, Wenlock Limestone . 72. Magellania Jlavescens, Recent. Interior of valves 73. Vertical section of shell of Magellania Jlavescens PAGE 89 89 90 91 94 95 96 97 100 106 108 109 113 114 116 117 119 122 123 126 131 132 135 138 141 142 144 147 148 150 151 152 152 152 153 153 156 161 162 163 165 168 X LIST OF ILLUSTRATIONS FIG. 74. Horizontal section of shell of Terebratula maxillata 75. Iphidea labradorica, Lower Cambrian . 76. Lingula anatina, Recent ..... 77. Crania anomala, Recent ..... 78. Productus giganteus, Carboniferous 79. Chonetes, Devonian ...... 80. Orthis (Schizophoria) striatula, Devonian 81. Pentamerns (Conchidium) knighti, Aymesfcry Limestone 82. Spirifer striatus, Carboniferous 83. Atrypa reticularis, Wenlock Limestone . 84. Rhynchonella (Hemithyris) psittacea, Recent. 85. Rhynchonella (Pugnax) acuminata, Carboniferous 86. Terebratula (Liotliyris) vitrea, Recent . 87. Terebratulina caput-serpentis, Recent 88. Stringocephalus burtini, Devonian . 89. Structure of Polyzoa ..... 90. A, Smittia landsborovi. B, Tubulipora fimbria, Recent 91. My a arenaria, Recent ...... 92. Meretrix (Callista) chione, Recent .... 93. Nucula, Trigonia, Spondylus, Lucina, Lutraria 94. Vertical section of shell of Unio .... 95. Section of prismatic layer of Pinna, Recent . 96. 97. Sections of Hippurites cornu-vaccinum, Cretaceous 98. Section of Tritonium corrugatum, Recent 99. Bellerophon, Carboniferous . 100. Nerinea trachea, Great Oolite 101. Hyolithes, Cambrian 102. Section of Sepia officinalis, Recent 103. Section of shell of Nautilus . 104. Central part of shell of Nautilus 105. Section of Actinoceras 106. Aperture of Gomphoceras bohemicum, Silurian 107. Sutures of Parkinsonia, Jurassic, and Ceratitcs, Trias 108. Central part of shell of an Ammonite 109. Aptychus of an Ammonite, Oxfordian 110. Glyphioceras spharicum, Carboniferous 111. Ceratites nodosus, Muschelkalk 112. Phylloceras heterophyllum, Lias 113. Suture of Phylloceras . 114. Lytoceras fimbriatum, Lias 115. Macroscaphites ivani, Lower Cretaceous 116. jEgoceras capricornus, Lias . 117. Harpoceras serpentinum, Lias PAGE 169 170 171 173 174 175 177 178 179 181 181 182 182 183 184 189 190 198 201 204 206 207 222 234 239 243 256 258 260 263 264 264 266 268 268 271 272 273 273 274 274 275 276 LIST OF ILLUSTRATIONS XI FIG. PAGE 118. Stepheoceras (Normanhites) braikenridgei, Inferior Oolite . 277 119. Cardioceras cordatum, Oxfordian 277 120. Section of guard and phragmocone of Belemnites . . . 281 121. Phragmocone and pro-ostracum of Belemnites . . . 282 122. Restoration of a Belenmite ....... 282 122 a. Arms of Belemnites, Lias 283 123. Calymene tuberculata, Wenlock Limestone .... 292 124. jEglina binodosa, Arenig Beds ...... 295 125. Calymene tuberculata. Ventral surface of head . . . 296 126. Hypostome of Asaphus tyr annus, Llandeilo Beds . . . 296 127. Thoracic segment of Asaphus expansus ..... 297 128. Under surface and limbs of Triarthrus becki, Ordovician . 299 129. Development of Trilobites 301 130. Paradoxides davidis, Menevian Beds ..... 301 131. Olenus cataractes, Lingula Flags . . .... 305 132. Asapthus tyrannus, Llandeilo Beds ...... 306 133. A cidaspis prevosti, Silurian ....... 309 131. Estheria minuta, Trias ........ 312 135. Cypris Candida, Recent ........ 313 136. Beyrichia complicata, Bala Beds 314 137. Lepas australis, Recent 316 138. Paranebalia longipes, Recent . ...... 319 139. Hymenocaris vermicauda, Lingula Flags .... 321 140. Caryocaris wrighti, Arenig Rocks ...... 322 141. Nyctiphanes norvegica, Recent ...... 324 142. Archaoniscus brodiei, Purbeckian ...... 325 143. Glyphea regleyana, Oxfordian ..... . 328 144. Ventral surface of Limulus polyphemus, Recent . . . 338 145. Dorsal surface of Limulus polyphemus, Recent . . . 339 146. Hcmiaspis limuloides, Ludlow Beds ..... 342 147. Dorsal surface of Pterygotus osiliensis, Silurian . . . 344 148. Ventral surface of same ....... 345 149. Restoration of ventral surface of Slimonia, Silurian . . 349 150. Ventral surface of Scorpio, Recent . ..... 351 151. Restoration of Palaophonus, Silurian ..... 353 DIVISIONS OF THE BRITISH STRATIFIED ROCKS Cainozoic or Tertiary Pleistocene . Pliocene Miocene (not Oligocene .... Eocene J Post-glacial deposits (river-gravels, cave-deposits, etc.) | Glacial deposits (Boulder Clay, etc.) Forest Bed Series Norwich Crag Series Red Crag Coralline Crag found in England) Hamstead Beds Bembridge Beds Headon Beds ' Bagshot, Barton, and Bracklesham Beds London Clay Oldhaven Beds Woolwich and Beading Beds V Thanet Sands Mesozoic or Secondary v er ) Chalk | Gault and Upper Greensand J Lower Greensand Cretaceous Lower Upper Jurassic I Wealden fPurbeckian Portlandian Kimeridgian Corallian V Oxfordian (with Kellaways Bock) / Cornbrash Forest Marble Middle., Great Oolite Series (Bathonian) V Lower Bradford Clay Great Oolite 1 Stonesfield Slate Inferior Oolite I Fuller's Earth Series \ Inferior Oolite (Bajocian) I Passage beds (sands) Lias Xlll Triassic IRhastic Series Keuper Series Muschelkalk (not found in England) Bunter Series Palaeozoic or Primary t, f Magnesian Limestone Series Permian J ° ( Sand J Upp( Sandstones, etc. Carboniferous I J Coal Measures I Millstone Grit Lower... Carboniferous Limestone Group Devonian and t Upper Old Ked \ Middle Sandstone ^ Lower Downtonian Series Silurian 4 Salopian Series Valentian Series Downton Sandstone Upper Ludlow Beds Aymestry Limestone Leintwardine Flags Lower Ludlow Beds Wenlock Limestone Wenlock Shale Woolbope Beds j Tarannon Shales | Llandovery Beds { Bala or Caradoc Series Ordovician \ Llandeilo Series i Arenig Series j Tremadoc Slates Cambrian Upper . Middle. Lower , i Lingula Flags | Menevian Beds | Solva Beds (upper part of Harlech Beds) Olenellus Beds INTRODUCTION From the earliest times it has been known that bodies resembling marine animals occur embedded in the rocks. For several centuries two distinct views were held respect- ing their nature. By some persons they were thought to have once formed parts of living animals, and con- sequently to indicate that the spot where they are now found was in past ages covered by the sea. Others, feeling it difficult to account for so much geographical change as would be necessitated by this view, considered that they were not of organic origin at all, but had been formed by some ' plastic force ' within the earth — that they were in fact ' Sports of Nature.' Since, however, these bodies re- semble in every essential respect the hard parts of animals now existing, we may at once reject this hypothesis. The remains of animals and plants of past ages pre- served in the rocks are known as fossils, the study of which forms the subject of Palaeontology. In order that an animal or plant may become a fossil two conditions are generally necessary : First, it must possess a skeleton of some kind or other, since the soft parts are rapidly decomposed ; consequently such animals as jelly-fishes leave no trace of their existence, unless it be a mere imprint. Secondly, the organism must be covered up by some deposit, otherwise it will soon crumble to pieces w. p. 1 2 INTRODUCTION Now, since there are comparatively few places on land where material is being deposited to any great extent, it follows that terrestrial animals will stand but little chance of being preserved ; the greater number after death will remain on the surface and will in a short time be entirely decomposed. A few may become entombed in peat-bogs, in the dust and ashes thrown out by volcanoes, in the sand of sand-dunes, or by a landslip ; some may be sealed up in deposits of carbonate of lime, such as the travertine thrown down by calcareous springs, or the stalagmite formed on the floor of caves ; and lastly, others may be transported by running water and ultimately buried in the bed of a river, of a lake, or of the sea. Such instances, however, are of comparatively rare occurrence. In the case of aquatic animals the conditions for fossilisation are much more favourable, since deposition is more universal in water than on land. Of such aqueous deposits, those formed in the sea will enclose by far the larger number of animals on account of the greater area which these deposits cover. The structure and composition of the hard parts vary considerably in different groups of animals and plants ; some are therefore much more readily preserved as fossils than others. Thus in Argon auta the skeleton consists of a thin shell which is easily broken up ; then again in some sponges it is formed of needles of silica, which are held together by the soft parts only and consequently easily become scattered after the death of the animal. But in other cases, as in most of the mollusks and corals, the skeleton is very strong and not easily destroyed, hence these occur abundantly in the fossil form. Perhaps even more important than the structure, is the composition of the hard parts, which, in the case of insects and some INTRODUCTION 3 hydroids consist of a horny substance known as chitin ; in diatoms, in most radiolarians, and in many sponges, of silica ; in the bones of vertebrates, chiefly of carbonate and phosphate of lime ; in corals, echinoderms, mollusks and many other animals and some plants, of carbonate of lime ; in most plants, of woody or corky tissue : a larger or smaller amount of organic matter is always combined with the mineral. Of these substances, chitin is with difficulty dissolved. Silica in its ordinary crystalline condition is one of the most' stable of minerals, but when secreted by an animal or plant it is glassy and isotropic (i.e. singly refracting and without effect on polarised light), and is dissolved with comparative ease, so that such skeletons may be entirely removed by the action of percolating water. In organisms with calcareous skeletons the car- bonate of lime is readily dissolved by water containing carbonic acid, but the degree of solubility varies according to the condition in which the carbonate of lime is present. In some animals it occurs as aragonite, in others as calcite. Of these two minerals, aragonite is the harder and heavier, its specific gravity being 2*93, whilst that of calcite is only 2*72 ; aragonite crystallises in the rhombic system, calcite in the hexagonal. Fossil calcite shells (e.g. Pecten opercularis) are translucent, their surface is compact, but their interior porous; on the other hand the aragonite shells (e.g. Pectunculus glycimeris) are opaque, and have a chalky appearance but a compact structure throughout. If a shell of each kind be suspended in water containing carbonic acid, it will be found that the one composed of aragonite will lose, in the same time, a much greater pro- portion of its weight than the other. Further, the calcite shell remains firm longer than the aragonite, the latter being soon reduced to the consistency of kaolin or china- 1—2 4 INTRODUCTION clay. This difference, however, does not appear to be due directly to mineral composition, for Cornish and Kendall found that when crystals of calcite and aragonite were powdered and placed in carbonic acid solutions of the same strength, the aragonite was not acted on more rapidly than the calcite, and the same result was obtained with powdered fossil shells. From all these considerations, it is not surprising to find that in some strata the aragonite skeletons have entirely disappeared, whereas those formed of calcite remain. This will obviously be most likely to occur in pervious beds through which water containing carbonic acid percolates. A striking instance of the differ- ence in the solubility of calcite and aragonite was furnished by some specimens of the common edible mussel, Mytilus edulis, in which the inner layer of the shell is formed of aragonite and the outer of calcite ; Sorby found specimens in the raised beach at Hope's Nose, Torquay, which had lost the inner layer but not the outer. Similarly, in speci- mens of Spondylus from the Chalk, the inner layer of the shell has been completely removed, but the outer is left. In some cases aragonite is replaced by calcite, but then the organic structure is entirely destroyed, and we get merely a mass of calcite crystals. Calcite is never replaced by aragonite. The mineral character of the skeleton of the chief calcareous organisms is as follows : — Foraminifera. — The vitreous forms consist of calcite, the porcellanous probably of aragonite. Porifera. — Calcareous sponges of calcite. Anthozoa. — The Alcyonaria are of calcite, except He- liopora, which is of aragonite ; the Madreporaria are of aragonite. INTRODUCTION 5 Echinoderma. — All of calcite. Poly 20a. — Chiefly calcite. Brachiopoda. — All of calcite. Lamellibranchia. — Many consist entirely of aragonite, but Anomia, Ostrea, and Pecten of calcite. In Pinna, Mytilus, Spondylus, Unio, and Trigonia, the inner layer is of aragonite, the outer of calcite. Gasteropoda. — The majority are formed of aragonite, but Scalaria and some species of Fusus are of calcite. In some {e.g. Patella, Littorina) the outer layer is calcite. Cephalopoda. — Nautilus, Spirula, and Sepia are mainly aragonite, as also were probably the Ammonites. Argo- nauta and the guard of Belemnites are calcite. Crustacea. — The shell consists of chitinous material usually containing calcite, and often some phosphate of lime. The condition in which fossils occur depends, as we have seen, on their original composition and on the material in which they are embedded. The chief types are the following : — 1. The entire organism preserved. Occasionally the soft parts of the organism are preserved as well as the skeleton, the whole having suffered very little change. Instances of this are, (a) the woolly rhinoceros and mam- moth found frozen in the mud and ice in Northern Siberia, and (6) insects and plants encased in fossil resin, known as amber, found in the Oligocene beds on the Baltic shores of Prussia and in the Tertiary beds near Cromer. 2. The skeleton preserved almost unchanged. Some- times when the skeleton alone is preserved, it remains 6 INTRODUCTION almost in its original condition, except that it has lost its organic matter. Thus the shells in the Pliocene beds of England differ from living ones only in being lighter, more porous and generally colourless. In some instances a certain amount of mineral matter, such as carbonate of lime, has been added to the skeleton, making it heavier and more compact. 3. Carbonisation. In some plants, and in animals with chitinous skeletons, such as graptolites, the original material usually becomes carbonised. The organism under- goes decomposition and loses oxygen and nitrogen, the relative percentage of carbon therefore increasing. The changes are similar to those which occurred during the conversion of vegetable matter into coal. 4. A mould of the skeleton. Sometimes the skeleton disappears entirely, a mould only remaining : this is especially the case when it consists of aragonite and is embedded in a porous stratum. After the shell of a mollusk has become covered up with sediment, and the soft parts have been decomposed, the interior becomes filled with the same material. Water containing carbonic acid subsequently percolates through the rock and carries away the shell as bicarbonate of lime, so that there is left only a mould of the interior and of the exterior, the space between the two being that which was originally occu- pied by the shell and, if filled with wax, will give an exact model of it. Excellent examples of this mode of fossilisation are seen in some mollusks from the Portland Oolite, e.g. Ceritliium and Trigonia. Sometimes after the shell has been removed the space left becomes filled up with mineral matter carried in by percolating water ; this INTRODUCTION 7 has the form of the original skeleton but obviously not its internal structure. The interior of the shells of foraminifera may, soon after the death of the animal, become filled with glauconite (silicate of iron and alumina) ; subsequently the shell itself often disappears, leaving only the internal cast. Glauconite occurs in this way in the various greensand strata, and also in some of the deep-sea deposits at the present day. Somewhat similarly the shells of sea-urchins occurring in the Chalk are sometimes filled with flint ; in such cases the shell when buried did not become filled with Chalk, but remained empty until flint was deposited in it from percolating water containing silica in solution. 5. Petrifaction. In some deposits the fossils show the minute structure as well as the form of the organism, but the original material of the skeleton has been replaced by another mineral. Thus we find fossil wood which shows the cells and vessels just as in existing trees, but in which the walls are formed of silica instead of cellulose. The change has gone on in such a manner that as each particle disappeared its place was taken by a particle of silica. The chief minerals which replace the original substance of organisms in this manner are : — (i) Carbonate of lime ; calcite sometimes replaces the silica of sponges. (ii) Silica, as in the fossils from the Blackdown Greensand, and the Thanet Sands near Faver- sham ; also in the wood of the Purbeck dirt-bed in the Isle of Portland. (iii) Iron pyrites; e.g. Ammonites from the Oxford Clay, Lias, etc., and some graptolites. 8 INTRODUCTION (iv) Oxide of iron, in the form of limonite in some fossils from the Dogger (Inferior Oolite) of York- shire and the Lower Greensand of Potton, etc., and as haematite in fossils from the Carboniferous Limestone of Cumberland. (v) In rare cases there are other replacing minerals, such as sulphate of lime, barytes, blende, galena, malachite, vivianite, and spathic iron. 6. Imprints. The footprints of animals and the impressions of jelly-fishes are sometimes found in the rocks, and these, although forming no part of the animal itself, are nevertheless regarded as fossils. In endeavouring to discover the changes which have taken place on the earth in past geological times, the evidence furnished by fossils is of primary importance. Each great group of the stratified rocks, known as a system, is characterised by a particular assemblage of genera and species, some of which are confined to it and enable us to identify the system. In a similar manner, the smaller divisions — the series and stages, are each characterised by the presence of certain fossils, which do not occur above or below. Further, it is found that the fauna of the smallest division (stage or group of beds) is not of uniform character throughout ; although there may be no change in the nature of the rock, some of the species and varieties which are abundant at one level will become rare or will disappear entirely in passing to higher or lower horizons. Consequently, a set of beds may be divided into belts or zones, the general aspect of the fauna of each zone being somewhat different from that of the others, but between these divisions there will be no break INTRODUCTION 9 either physical or pakeontological. If then we have determined the order of succession of the formations in any one area by means of their relative positions, the newer resting on the older, it is fairly easy in any other district, merely by examining the fossils, to refer any set of beds to its proper position in the geological record. But although this law of the identification of strata by the fossils which they contain is of great value, it must not be applied without some caution, for even if two formations were deposited at exactly the same time, it does not necessarily follow that all the genera and species found in the two will be identical. Thus for instance in the seas at the present day the same forms of life do not occur in all parts ; animals which live in water of moderate depth are distributed in provinces which depend largely on climatic conditions, each province possessing some forms peculiar to itself. The organisms now being entombed in deposits formed, say, off the British coasts, will as a whole be different from those off the Canary Islands ; but still, some of the species and many of the genera will be common to both areas, and would enable us to identify the two deposits as having been formed within the same general period, though perhaps not to prove them abso- lutely synchronous. Then again there is a distribution of organisms according to the depth of the sea, and the nature of the sea-bottom; so that the fauna of a deep- water formation will necessarily be different from that of a shallow-water one, and that of a sandy deposit different from that of a mud. But in addition to the animals living on the sea-bottom there are others which live near the surface of the ocean, far from land ; such pelagic forms have a wider geographical range than those which live on the sea-floor in shallow water, and are consequently of 10 INTRODUCTION great value in determining, as of the same age, deposits found in widely-separated localities. In addition to their chronological value, fossils are also important in indicating the conditions under which the formations were deposited. In the case of the later beds, where most of the fossils belong to genera which are still existing, it is easy to distinguish a marine deposit from one formed in freshwater or on land. Even in the rocks of earlier periods, in which most of the genera are extinct, we may recognise a marine deposit by the presence of such animals as radiolarians, corals, echinoderms, brachiopods, pteropods, cephalopods, or cirripeds, which at the present day are found only in the sea. The depth of the sea in which a formation was deposited can be estimated when the fossils belong to living species ; when the species are extinct some idea may be formed if the genera to which they belong are found chiefly at some particular depth at the present day. In attempting such determinations it must be remembered that the sea-bottom down to a depth of nearly 50 fathoms may be disturbed by the action of waves and currents in the sea ; consequently the animals living on the bottom in shallow water are liable to be carried from their original home to higher or lower levels. One of the surest indications that a formation was laid down in shallow water and not far from land is furnished by the association of the fossil remains of land animals and plants with marine species; another, by the presence of mollusks such as Pholas, Saxicava and Lithodomus, which bore into rocks, and at the present day are found only in shallow water. The nature of the climates of past ages may be judged to some extent by the character of the fossils ; the evidence furnished by land-plants is particularly valuable, since INTRODUCTION 11 their distribution is determined largely by temperature and is better marked than in the case of marine animals. As far as the latter are concerned it is only when we are dealing with modern species that we can, as a rule, speak with any degree of certainty on this subject; this is owing to the fact that at the present day the individual species of the same genus have often a very different distribution, some being found in warm, others in cold, regions. Even when all the fossils in a formation belong to extinct species, the assemblage of genera is sometimes such as marks some region at the present day ; thus, for example, in the London Clay we find that many of the genera of mollusks are now characteristic of tropical or subtropical seas. The study of fossil animals and plants is of the highest importance to the biologist, not only because they are the ancestors of modern species, but because among fossil forms we find many groups {e.g. Graptolites, Cystids, Blastoids, Trilobites, Eurypterids), which are altogether extinct, and which often throw light on the relationship of existing animals and plants. Others (e.g. Crinoids, Brachiopods, Nautiloids) are represented at the present day by few forms only, but were, in past ages, very abundant ; consequently no adequate knowledge of such groups of animals can be obtained from the study of living examples only. In some cases the ancient forms serve to connect groups which, at the present day, appear to be quite distinct ; thus, for example, the earliest known bird (Archoeopteryx, from the Solenhofen Limestone, Upper Jurassic) shows, in several important characters, affinities to the Reptiles. From the point of view of the biologist, the greatest interest in Palaeontology is found in the bear- ing it has on the subject of evolution : it is only by a study 12 INTRODUCTION of the fossil forms that the race-history or phylogeny of animals and plants can be traced with certainty ; but in attempting such investigations a great difficulty is pre- sented by the imperfection of the record of the life of past ages, since only a very small proportion of the animals and plants has been preserved, and these often in a very imperfect manner. We have already seen several reasons why this record must be imperfect ; some animals are with- out hard parts, while others, particularly land animals, do not become covered up with sediment. Further, the remains of animals which were originally present in the rocks have been, in some cases, dissolved by percolating water, or to a great extent obliterated by the meta- morphism which the rock has undergone. Then again the record of life is incomplete because of the breaks in the succession of the stratified rocks ; these breaks have been caused sometimes by denudation having removed a great thickness of rocks, in other cases by an absence of deposition. Notwithstanding this imperfection of the record, many groups of animals are found to undergo gradual modification when traced through series of strata or formations. For example, in the Pliocene deposits of Slavonia there are numerous shells of pond-snails (Vivi- parus or Paludina) ; and specimens found at the top and bottom of the formation, and also at certain intervening levels, differ so much from one another that they appear to belong to distinct species. When, however, examples are collected from all the beds of the formation, the apparently distinct species are seen to be connected by intermediate forms, and a series, showing a gradual passage from the species found in the lowest bed to that in the highest, can be obtained. In several groups of Tertiary Mammalia there is also INTRODUCTION 13 evidence of gradual modification in structure ; thus the earliest known forerunner of the horse, found in the Eocene beds, possessed five toes, and was succeeded in later times by forms with successively fewer toes, until in the Pliocene, the existing type (Equus), with only one toe and splint-bones, appeared ; other gradual changes also occurred in the character of the teeth, etc. In the development and growth of an animal, various stages, which often present some resemblance to the adults of other animals, are passed through. In some cases these stages in the life of the individual are also similar to those which occurred in the history of its race, as shown by the geological record. This agreement gives some support to the ' recapitulation theory,' which sup- poses that the changes passed through in the development of the individual (ontogeny) are, in a general way, a rapid and incomplete repetition of those which occurred in its race-history (phylogeny). In a natural classification of animals an attempt is made to place together in the same group those forms which are connected by descent ; such a classification, if perfect, would be of the nature of a genealogical tree. Each main division is termed a Phylum, and is divided and subdivided into smaller and smaller groups, known as Classes, Orders, Families, Genera, and Species. A species includes a group of individuals which appear to have descended from the same ancestors and can give rise to offspring which are fertile among themselves ; such indi- viduals usually differ from one another to only about the same degree that offspring of the same parents may differ. One species is generally distinguished from another by such characters as ornamentation, shape, relative propor- 14 INTRODUCTION tion of parts, and size. In some species one or more groups termed varieties may be recognised, and are dis- tinguished from the other forms included in the species by some slight, but fairly well-marked and constant modification. Varieties are frequently connected with the special physical or biological conditions under which they are living. The varieties in some species pass into one another by intermediate forms ; but others appear to be fairly distinct and may be regarded as incipient species. Sometimes two groups of individuals resemble each other so closely that they might be regarded as belonging to the same genus or to the same species, but they appear to have descended from different ancestors since they are found to differ in development (ontogeny) or in their palgeontological history ; this phenomenon, of forms belonging to different stocks, approaching one another in character, is known as convergence or heterogenetic homceo- morphy, and may occur either at the same geological period or at widely separated intervals. Similarly, animals belonging to two distinct groups may, when subjected to similar conditions, show corre- sponding modifications, though they do not really approach one another in essential characters ; thus parallel modifi- cation may occur in independent groups. PHYLUM PROTOZOA Classes Orders ( 1. Foraminifera. 1. Gymnomyxa J 2. Eadiolaria. (Sarcodina) [ 3. Others not found fossil. 2. Flagellata or Mastigophora (not fossil). 3. Infusoria (not fossil). 4. Sporozoa (not fossil). The Protozoa include the lowest forms of animals, such as Amoeba, Vorticella, and Globigerina. The body is usually very small, and consists in many cases of one cell only, in others of more than one, but the cells never form tissues as they do in all other animals. A cell consists of proto- plasm— a viscid or semi-fluid living substance containing granules ; in the centre of the cell is a denser, usually spherical body called the nucleus — sometimes more than one is present. In some Protozoa (the Gymnomyxa) the protoplasm is naked, and consists of an inner granular mass and a thin, clear, outer layer ; such forms are further characterised by having no definite shape, by being able to take in food at any part of the body, and by possessing the power of throwing out lobes or filaments of protoplasm known as pseudopodia. In others (the Flagellata and Infusoria) the protoplasm is surrounded by a firm membrane or cuticle which gives the animal a definite form ; the food is generally taken in at one permanent aperture, and 16 PROTOZOA. FORAM1NIFERA pseudopodia are seldom present, but the surface is provided with cilia or flag ella, which are fine threads of protoplasm having a definite form and a rhythmic movement. Reproduction in the Protozoa takes place usually by fission (i.e. division into two parts) and sometimes by the formation of spores. In some cases conjugation of two or more individuals occurs, representing to some extent sexual reproduction. In some of the Protozoa there is no skeleton, but in others a shell is formed. The Protozoa can be divided into four main groups, (1) the Gymnomyxa, (2) the Flagellata, (3) the Infusoria, (4) the Sporozoa ; no examples of the last three divisions have been definitely recognised in the fossil state. CLASS I. GYMNOMYXA (SARCODINA) The members of this group possess no external mem- brane (cuticle), and are able to throw out pseudopodia, by means of which movement takes place and food is obtained. The Gymnomyxa or Sarcodina are divided into several orders, of which only two have been found fossil, namely, the Foraminifera and the Radiolaria. ORDER I. FORAMINIFERA The Foraminifera are characterised by their thread-like pseudopodia, which frequently branch and anastomose ; and by possessing in most cases a shell or test, which may be calcareous, arenaceous, or chitinous. The calcareous forms are by far the commonest, and in these, two kinds of shell may be distinguished, namely, the vitreous and the -porcellanous. In the vitreous, the PROTOZOA. FORAMINIFERA 17 shell has a glassy appearance, and is perforated by in- numerable tubes for the passage of the pseudopodia; in some forms {e.g. Rotalia) these tubes are ^^ of an inch in diameter, but in others (e.g. Operculina) only 16^00 of an inch. In the porcellanous forms the shell, when viewed by reflected light, is opaque and white, having the appearance of porcelain ; it is not perforated by tubes, but possesses one or two large apertures through which most of the pseudopodia pass out — some, however, are given off from the layer of protoplasm which covers the surface of the shell. In these porcellanous Foraminifera the shell is sometimes pitted, producing at first sight the appearance of perforation. In the arenaceous forms the shell consists of foreign particles joined together by a cement. The particles are usually grains of sand (commonly quartz), but sometimes sponge spicules, or the shells of other Foraminifera. The cement may be formed of chitinous, calcareous, or ferruginous material. The shell is often imperforate. The chitinous forms (e.g. Gromia) do not occur as fossils. The shell of the Foraminifera varies considerably in form and structure ; in some genera it consists of a single chamber, when it is said to be unilocular, as for example in Orbulina, where it is spherical, and in Lagena (fig. 3, F), where it is generally flask-shaped. In other cases it consists of several chambers communicating with one another, either by perforations in the walls (septa) between them, or by larger openings. In these multi- locular forms the shell grows by the addition of a new chamber at the end of the one last formed ; this takes place by the protrusion, through the aperture or mouth of the shell, of a mass of protoplasm, at the surface w. p. 2 18 PROTOZOA. FORAMINIFERA of which the wall of a new chamber is formed either by the secretion of material or by cementing of foreign particles. The arrangement of the chambers in the multilocular Foraminifera is very varied; they may be placed in a straight line as in Nodosaria (fig. 3, H), in a curved line as in Dentalina, in a plane spiral as in Cristellaria (fig. 3, 67), or in a helicoid spiral as in Rotalia (fig. 3, L, M). The earlier whorls in some spiral forms are partly or entirely covered by the later ones, so that sometimes the last whorl only is visible on the exterior {e.g. Cristellaria) ; but when the later chambers are merely attached to the extremities "0 Fig. 1. A, section of a foraminifer in which each septum is formed of a single lamella. B, in which the septum is formed of two lamellas. a, passages between the chambers ; b, septum ; c, anterior wall of last chamber ; d, supplemental skeleton. (After Carpenter.) of the earlier ones, all the whorls can be seen (e.g. Operculina). Some genera, such as Textularia (fig. 3, E), have two rows of chambers placed side by side ; others (Tritaxia) have three. In some cases (e.g. Orbitolites) there are numerous chambers arranged in concentric rings instead of in a spiral. In the porcellanous and the simpler vitreous Forami- nifera each septum (fig. 1, A, b) consists of a single lamella PROTOZOA. FORAMINIFERA 19 which is really the front wall of the preceding chamber; but in the higher vitreous forms each septum (fig. 1, B, b) is formed of two lamellae, owing to the fact that when a new chamber is added to the shell a new wall is secreted next to the front wall of the last chamber. The shell of the vitreous Foraminifera is at first thin, but may after- wards increase in thickness by the addition of material at the surface ; in the higher vitreous forms the outer layers are often traversed by numerous canals and constitute what is known as the supplemental skeleton (fig. 1, B, d). A B Fig. 2. Dimorphism of Nummulites Icevigatus, Brackleshani Beds (Eocene), Selsea. A, section of the entire shell of the megalospheric form x 9. B, section of the central part of the microspheric form x 9. Most of the higher Foraminifera are dimorphic — that is to say, there are two forms of the same species. This fact was first noticed in specimens of Nummulites from the Eocene deposits. In one form, the first or initial chamber, which is seen at the centre when the shell is split, is large and more or less spherical and is called the megalosphere (fig. 2, A); in the other it is much smaller and is known as the microsphere (fig. 2, B). These two forms are found associated together, and were, at one time, described as different species. In the microspheric type the shell . 2—2 20 PROTOZOA. FORAMINIFERA commonly, but not always, grows to a larger size than in the megalospheric type, and individuals of the former are much less numerous than of the latter ; in other respects the two are similar. The relationship of the microspheric and megalospheric shells has been elucidated by a study of the life-history of Polystomella and other living Forami- nifera. When reproduction takes place in the microspheric form all the protoplasm passes out of the shell and divides into spherical masses, each of which secretes a shell and develops into a megalospheric individual. In the repro- duction of the megalospheric form the protoplasm divides into small rounded portions which pass out of the shell as moving spores — zoospores ; it is believed that two zoospores from different individuals conjugate and give rise to a microspheric individual. There are, therefore, two modes of reproduction — asexual and sexual, which alternate. For convenience of reference the Foraminifera may be divided into three groups, the characters of which are based on the structure and composition of the shell ; but this cannot be regarded as a natural classification since in some types which are usually calcareous {e.g. Miliola) we occasionally meet with species in which the shell consists largely of sandy material. I. Porcellanous Forms. Shell calcareous, porcellanous, not perforated by canals, but provided with one or two large apertures through which the pseudopodia pass out. Miliola. (fig. 3, A — D.) Shell multilocular, the chambers being coiled on an elongated axis, each chamber forming half a convolution. In some cases all the chambers are visible externally on both sides of the shell (fig. 3, D) ; in others, owing to the lateral prolongations of the chambers, only the last one or two are Fig. 3. Foraminifera (recent). A, B, Biloculina depressa. B, section. C, Miliolvna seminulum. D, Spiroloculina limbata. E, Textularia barretti. F, Lagena sulcata. G, Cristellaria rotulata. H, Nodo- saria radicula. I, K, Globigerina bulloides. L, M, Rotalia beccari. (After Brady.) All enlarged. 22 PROTOZOA. FORAMINIFERA seen (fig. 3, A, C) ; or it may be that more chambers are shown on one side than on the other. The external features of the shell consequently vary considerably, and on this account the forms in- cluded under the term Miliola are now regarded as constituting a number of distinct genera to which the following names have been given : — Biloculina, Fabularia, Spi?'oloculina, Ifiliolina, Quinquelocu- lina, etc. Trias to present day. Ex. Miliolina seminulum, Eocene to present day ; Biloculina ringens, Eocene to present day ; Spiro- loculina planulata, London Clay to present day. Orbitolites. Shell discoidal, generally rather large, composed of either a small spiral part at the centre, or of one or more large central chambers, around which are many concentric rings divided into numerous chambers ; the chambers of adjacent rings communicate by radial openings, and at the external margin of the last ring are pores opening to the exterior. Above and below this layer of chambers there may be another layer of smaller chambers, arranged concentrically. Upper Cretaceous to present day. Ex. 0. compla- nata, Eocene. Alveolina. Shell fusiform or elliptical, sometimes nearly globular, composed of many whorls coiled around the long axis of the shell ; each whorl completely covers the one preceding it, and is divided into long chambers by partitions parallel with the axis of the shell ; these are divided into smaller chambers by partitions at right angles to the others. Chalk to present day ; chiefly Eocene. Ex. A. boscL Eocene. II. Arenaceous Forms. Shell composed of grains of sand or other particles cemented together by chitinous, calcareous, or ferruginous material. Saccammina. Shell usually free, compact, formed of a single spherical, pyriform, or fusiform chamber with a projecting aperture, or of a number of chambers united end to end. Surface smooth or nearly smooth. Ordovician, Carboniferous, and living. Ex. S. fusuliniformis (= carter?'), Carboniferous Limestone. PROTOZOA. FORAMINIFERA 23 Lituola. Shell free, composed of coarse grains, spiral or crosier-shaped. Septa labyrinthine. Aperture simple or sieve-like. Carboniferous to present day. Ex. L. nautiloidea, Chalk. Orbitolina. Shell partly sandy, conical or flattened, with convex upper, and usually concave lower surface ; consisting of central compressed chambers surrounded by concentric rings of chambers. Cretaceous. Ex. 0. concava, Upper Greensand. Endothyra. Shell free, spiral )similar to Rotalia) ; chambers numerous, composed of an outer calcareous, perforated layer, and an inner compact layer formed of small grains cemented together. Aperture at the inner margin of the last chamber. Carboniferous to Trias. Ex. E. bowmani, Carboniferous Limestone. Textularia. (fig. 3, E.) Shell arenaceous (in the small forms it is vitreous) ; form variable, conical, pyriform, or cuneiform ; composed of numerous chambers in two alternating parallel series. Aperture slit-like on the inner edge of the last chamber. Cambrian to present day. Ex. T. globidosa, Chalk. III. Vitreous Forms. Shell of calcite, vitreous, perforated by numerous minute canals for the passage of the pseudopodia. Lagena. (fig. 3, F.) Shell unilocular, very finely perforated. Form globose, ovate or flask-shaped. A single terminal aperture, sometimes at the end of a long neck ; rarely two apertures. Surface smooth, ribbed, striated, or spinous. Cambrian to present day. Ex. L. striata, London Clay to present day ; L. sulcata, Silurian to present day. Nodosaria. (fig. 3, H.) Shell composed of a number of chambers which are circular in transverse section, arranged in a straight line, and separated by constrictions. Aperture at the apex of the last chamber. Surface smooth or ornamented with granules, spines, or ribs. Cambrian to present day. Ex. N. zippei, Gault and Chalk. Cristellaria. (fig. 3, G.) Shell compressed, lenticular or elongate, multilocular, coiled in part or entirely in a plane spiral ; 24 PROTOZOA. FORAMINIFERA each coil usually covers the one preceding it. Cambrian to present day. Ex. C. rotulata, Chalk. Globigerina. (fig. 3, 7, K.) Shell perforated by large canals ; chambers globular, few, arranged in a plain or helicoid spiral, each chamber opening by a large aperture into the central cavity of the spire. No supplemental skeleton. Pelagic forms usually with spines. Cambrian to present day. Ex. G. cretacea, Chalk. Orbulina. A single spherical chamber, with perforations of two sizes. Sometimes with smaller chambers (similar to a Globi- gerina) inside the large spherical one. Lias to present day. Ex. 0. universa, Lias to present day. Rotalia. (fig. 3, L, If.) Test very finely perforated, multi- locular. The chambers arranged in a helicoid spiral, so that on the upper surface all the whorls are seen, on the lower only the last one. The aperture is in the form of a curved slit on the lower surface of the last chamber. The septa are usually formed of two layers. A supplemental skeleton is often present. Lower Cretaceous to present day. Ex. R. beccari, Miocene to present day. Calcarina. Test lenticular, spiral, with only the last whorl visible on the base. Supplemental skeleton greatly developed, traversed by numerous canals, and projecting as long spines from the margin. Chalk to present day. Ex. C. calcitrapoides, Chalk. Fusulina. Shell fusiform, composed of elongated whorls ; each whorl completely covers the preceding one, and is divided by septa into a number of chambers, which may be again divided into smaller chambers. Adjoining chambers communicate by a slit at the middle of the base of each septum. Septa folded, each consisting of a single layer. Aperture in the form of a fissure. Carboniferous and Permian. Ex. F. cylindrical Carboniferous Limestone. Amphistegina. Shell lenticular, with sharp edge ; the upper and lower surfaces unequally convex ; formed of numerous chambers coiled in a plane spiral, each coil almost completely enclosing the preceding one. Septa formed of a single layer. Supplemental skeleton at the centre of the shell. Aperture similar to that of Rotalia. Carboniferous, and Miocene to present day. Ex. A. haueri, Miocene. PROTOZOA. FORAMINIFERA 25 Nummulites. (figs. 2, 4.) Shell lenticular in form, and com- posed of a large number of whorls coiled In a plane spiral. Usually each whorl completely covers the preceding one by means of the lateral prolongations of the chambers, so that externally only the last whorl of the shell is visible. The whorls are divided into chambers (c) by septa (b) which are slightly curved backwards ; each chamber communicates with the neighbouring one by means of a median fissure at the inner margin of the septum. Each septum is formed by two lamellae. A supplemental skeleton is present, part of it forming what has been termed the ' marginal cord ' (a). The general shell-substance is minutely perforated, and a system of canals also traverses the septa and supplemental skeleton. Aperture a, mar- Fig. 4. Nummulites, showing vertical and horizontal sections. ginal cord with canals (supplemental skeleton); b, septum, with canals ; c, chambers ; d, test ; e, pillars of the supplemental skele- ton. (After Zittel.) Enlarged. in the form of a slit at the inner margin of the last chamber. The shell splits readily into two similar parts along the median plane, owing to the relatively large size of the parts of the chambers occurring there. The earliest species of Nummulites occurs in the Carboniferous Limestone of Belgium ; others have been recorded from the Upper Jurassic of Amberg (Bavaria) ; the genus attains its maximum in the Eocene ; only one or two rather rare forms are living, one of which (N. cummingi) is found in shallow water in 26 PROTOZOA. FORAMINIFERA tropical and sub-tropical regions. In the English Eocene the genus is found in the Barton and the Bracklesham Beds. Ex. N. Icevigatus, Bracklesham Beds. Operculina. Similar to Nummulites, but whorls fewer and rapidly enlarging, all visible externally ; each of the earlier whorls partly encloses the preceding one. Cretaceous to present day. Ex. 0. complanata, Miocene. Orbitoides. Test lenticular or discoidal, composed of a median layer of rectangular chambers arranged in concentric rings which are often incomplete ; the chambers of adjacent rings com- municate by oblique passages. Above and below this layer are numerous layers of smaller chambers ; these chambers are flattened and irregular in form, placed one above the other in piles, and arranged more or less concentrically. The test is minutely per- forated, and canals traverse the septa and marginal cord as in Nummulites ; the septa are also formed of two lamellse. Chalk to Miocene ; chiefly Eocene. Ex. 0. papyracea, Eocene. Distribution of the Foraminifera. The majority of the Foraminifera are marine, most of them living on the sea-bottom. A few however, as for instance Globigerina, exist at or near the surface in the open ocean, and these are very important on account of their abundance. The distribution of the Foraminifera which live in the open ocean, as well as those found in shallow water, is influenced largely by temperature ; the former are more numerous in the warm ocean-currents than in colder water, whilst the species of the latter often have their range determined by temperature. The Foraminifera found in the Palaeozoic deposits are mainly vitreous and arenaceous forms. They appear first in the Lower Cambrian rocks, but are comparatively rare until the Carboniferous, in which some beds are formed PROTOZOA. FORAMIXIFERA 27 largely of their shells, as for instance, the Saccammina- limestone of the north of England and Scotland, the Endoth ^ra-limestone of North America, and the Fusulina- limestone of Russia, China, Japan and North America. The Foraminifera are mostly of small size in the Permian of England ; they are comparatively rare in the Trias, but become abundant in the Jurassic, where, however, rock- building types are generally absent. In the Lias the introduction of numerous vitreous species {Nodosaria, Cristellaria etc.), many of which appear to be allied to forms now living in tropical or warm-temperate regions only, is noteworthy ; some porcellanous forms belonging to the Miliola group are also fairly common. A larger number of genera and species are found in the Middle and Upper Jurassic than in the Lias. The Order continues to be well represented in the Cretaceous formations, particularly in the Gault and Chalk — Orbitolina, Ccdcarina, Globigerina, Rotalia etc. being common. Some beds of the Chalk, especially the Micraster zones and the Chalk Rock, are largely composed of Foraminifera such as Globigerina, Textularia, Bolivina, Flabellina. The Foraminifera attain their greatest development in Tertiary and recent times. In the Eocene deposits Niimmulites is often extremely abundant and of large size, forming the greater part of the massive Nummulitic Limestone of Southern Europe, Egypt, Asia Minor, and the Himalayas ; Miliola, Orbitolites, Alveolina, Operculina, and Orbitoides are also important rock-building forms in the Eocene period. In the English Eocene, Foraminifera are numerous in the Thanet Sands and the London Clay ; in the Barton and Bracklesham Beds Niimmulites, Miliolina, Alveolina etc. occur. Amphistegina is abundant 28 PROTOZOA. FORAM1NIFERA in the Miocene. A large number of forms occur in the Pliocene deposits of East Anglia and of St Erth in Cornwall. The genera and species of the Foraminifera have generally, as might be expected from their low organisa- tion, a long range in time ; some of the species which occur in the Palaeozoic are still living. ORDER II. RADIOLARIA In the Radiolaria the body consists of a central mass of protoplasm, enclosed in a membrane known as the central 3 Fig. 5. Heliosphara inermis. x 350. Recent. (After Biitschli.) 1, skeleton ; 2, central capsule ; 3, nucleus. Pseudopodia project from the surface. capsule (fig. 5, 2). The intracapsular protoplasm contains one or more nuclei, and is continuous, through pores in the capsule, with a layer of protoplasm outside the cap- sule ; this layer gives off thread-like pseudopodia, which occasionally unite. A skeleton (fig. 5, 1) is generally present, composed either of silica, or a peculiar horny PROTOZOA. RADIOLARIA 29 substance known as acanthin. The form of the skeleton varies considerably (fig. 6) ; it may be entirely outside the central capsule or partly within, and consists either of isolated spicules, or of a lattice-like or reticulate structure of varying shape, frequently with projecting spines. The Radiolaria do not live in fresh water, but they have a very wide distribution in the sea, where they are found in all climates and at all depths, showing the greatest variety of form in tropical regions. In some of the deeper parts of the Pacific and Indian Oceans the mm* to3 ~ doom/ Fig. 6. Fossil Radiolaria. A, Lithocampe tschernyschewi, Devonian. B, Trochodiscus longispinus, Carboniferous. C, Podocyrtis schom- burgki, Barbados Earth (Tertiary). All largely magnified. empty shells of these animals settle and accumulate on the sea-bottom, forming a siliceous deposit known as ' Radio- larian ooze.' Only those Radiolaria in which the shell consists of silica are preserved as fossils. Cayeux has described as Radiolaria some bodies found in the Pre-Cambrian rocks of Brittany; they are much 30 PROTOZOA. RADIOLARIA smaller than later forms of the group, and are thought by some authors to be simply inorganic aggregations. In Britain the earliest examples of the Radiolaria occur in the Ordovician rocks of the south of Scotland, where they form beds of chert ; others which are perhaps of nearly the same age, have been found in a chert from Mullion Island (off the west coast of the Lizard). A few specimens have been noticed in the Carboniferous Lime- stone of Flintshire, whilst in the Lower Culm of Devon and Cornwall these organisms contribute largely to the formation of thick beds of siliceous rock (cherts, etc.). At several localities on *the continent Radiolaria are fairly common in the Mesozoic formations, but in England only a few have been recorded from the Lias, the Lower Green- sand, the Upper Greensand, the Cambridge Greensand, and the Chalk. In the Tertiary some have been obtained from the London Clay of Sheppey. A very important Radiolarian formation of late Tertiary age covers large areas in the Island of Barbados, and is known as the ' Barbados Earth ' ; it resembles very closely the modern Radiolarian ooze mentioned above, and is probably a deep- sea deposit. » PHYLUM PORIFERA Classes. Hexactinellida. 2. Demospongise Orders. ' 1. Myxospongida. 2. Ceratosa. 3. Monaxonida. 4. Tetractinellida. 5. Lithistida. 6. Octactinellida. \ 7. Heteractinellida. 3. Calcarea (Calcispongiae). Sponges vary greatly in form, size, and complexity of structure. A simple type is similar to a vase or hollow sac, fixed by the lower end, and with an opening or osculum at the upper extremity. The wall of such a sponge is thin, and perforated by a- large number of pores through which water flows into the central or g astral cavity and passes out by the osculum ; by this means the sponge is provided with food and oxygen and gets rid of waste matters. The wall of the sponge consists of two layers — an outer or dermal and an inner or gastral ; the dermal (fig. 7, 2) is formed of a surface-layer of flattened cells, with a gelatinous layer beneath containing various cells, some of which secrete the elements of the skeleton. The gastral layer (fig. 7, 3) consists of a single layer of cells, each cell being provided with a collar-like projection, in the centre of 32 PORIFERA which is a long flagellum ; the circulation of water through the sponge is produced by the movements of these flagella. A simple form like that just described is found in the Fig. 7. Vertical section through Leucosolenia. Highly magnified. (From Minchin.) 1. Sieve-like memhrane covering the osculum ; 2. Outer layer ; 3. Collar or flagellated cells (the pointer should have been continued to indicate the cells lining 5) ; 4. Spicules; 5. Gastral cavity. POMFERA 33 young stages of many sponges which afterwards, in their adult condition, are much more complex. Owing to the growth of the sponge-wall being unequal in different parts, either folds or tube-like projections are formed, and these subsequently become more or less completely fused, so that the wall is much thickened (fig. 8) and is traversed by canals which are really spaces enclosed between the folds and outgrowths. In such forms the flagellated cells Fig. 8. Section of a portion of Grantia. Highly magnified. (From Dendy.) 1. Openings of inhalent canals ; 2. Inhalent canal ; 3. Openings of inhalent canals into flagellated chamber ; 4. Flagel- lated chamber; 5. Collar cells; 6. Spicules; 7. Exhalent opening of flagellated chamber. are frequently confined to chambers in the sponge-wall (fig. 8, 4). Canals, called incurrent or inhalent canals (2); pass from the surface of the sponge to these chambers, and others, the excurrent or exhalent canals, may lead from the w. p. 3 34 PORIFERA chambers and open into the gastral cavity. Further complications, such as branching of the canals, may occur. The thick wall of these more complex sponges is formed mainly of the gelatinous layer. In a sponge consisting of a single individual, the form depends mainly on the relative rates of growth in different directions, and may be cylindrical, vase-like, globular, discoiclal, etc. In a compound sponge the form depends also on the way in which the young individuals of the colony are attached to the parent, and in addition, on their remaining free or becoming fused together ; in the latter case the individuals of the colony are frequently dis- tinguishable by their oscula only; when the individuals remain free, arborescent or bushy colonies may result ; if they become fused, the sponge may be fan-shaped, funnel- shaped, cup-like, tubular, mushroom-shaped, massive, en- crusting, etc. Nearly all sponges are attached to some foreign object — generally by the base of the sponge, but in forms which are fixed in the mud, especially deep-sea forms of the Hexactinellida, and in some Tetractinellida, this fixation is by means of a root-tuft or rope of long spicules. In nearly all sponges there is a skeleton, which serves to support the canals and chambers and also for protection. This skeleton may consist of fibres of a horny substance, similar to silk in composition, and known as spongin; or of mineral particles, termed spicules (fig. 8, 6), composed of carbonate of lime or of colloid silica ; or it may consist of both siliceous spicules and spongin. Those forms only which have either a siliceous or calcareous skeleton are definitely known as fossils. Each spicule consists of a number of rays or arms, coming off from a centre, which is the point where the formation of the spicule commenced. PORIFERA 35 In some groups, as for instance in the Monaxonida and Tetractinellida, the spicules are not united or are joined by spongin only ; but in others they are fused together or interlocked so as to form a complete scaffolding, and generally it is in these only that the external form of the sponge has been preserved in the fossil state. In most siliceous sponges, two kinds of spicules may be distin- guished, the skeletal- spicules or megascleres which build the main part of the skeleton, and the flesh-spicules or microscleres which are smaller and isolated and are seldom preserved as fossils. In the axis of each spicule there is a canal known as the axial canal (fig. 9, c), which in the living sponge is occupied by a thread of organic matter ; this is the first part of the spicule to be formed, the mineral matter being subsequently deposited around it. The spicules of recent siliceous sponges are characterised by the glassy appearance of their surface, and by the silica being colloidal, isotropic, and soluble in heated caustic potash. But in the fossil state the spicules have generally undergone considerable change ; occasionally their silica is still colloidal but the surface has no longer the glassy appearance, and the axial canal is frequently filled with secondary silica in a crystalline or crypto-crystalline con- dition, and is consequently easily distinguished by the aid of polarised light when the spicule itself still remains colloidal. Generally, however, the spicule has become crystalline or crypto-crystalline, and in such cases the axial canal can rarely be detected since it is filled with material in the same condition. Sometimes the silica of the spicules has been entirely removed, a hollow cast only remaining ; in other cases it is replaced by another mineral, as for instance by calcite in the sponges from the Lower Chalk of Folkestone, by iron pyrites in Protospongia from the 3—2 Fig 9 Sponge spicules (skeletal), a, monaxonid, Halichondna pamcea, Recent. 6, tetractinellid, Paekastrella, Upper Greensand. c, te- tractinellid, Geodites, Eocene, d, lithistid, Scytaha radiciformis, Chalk e, lithistid, Seliscothon mantelli. f, hexactinelhd, Ccelop- tychium agaricoides, Chalk, g, octactinellid, Astneospongia, Silurian. ft, heteractinellid, Asteractinella expansa, Carboniferous, j, calci- sponge, Grantia compressa, Recent. All magnified. PORIFERA 37 Menevian Beds of St David's, by iron peroxide in the sponges of the Upper Chalk of the south of England, and by glauconite in some from the Upper Greensand. Obviously then, the colloidal silica of recent sponges is anything but a stable substance, thus differing widely from crystalline and crypto-crystalline silica. The spicules of the calcareous sponges are usually smaller than those of the siliceous forms, and their material is not in an isotropic state, but each spicule possesses the optical characters of a crystal of calcite ; consequently in polarised light these spicules are readily distinguished from unaltered siliceous forms, which appear dark between crossed Nicol's prisms. Then again the fossil calcareous spicules have undergone much less chemical change than the siliceous ones ; generally they are still composed of carbonate of lime, for it is only in rare cases that this is replaced by silica. The external form of the individual calcareous spicules is, however, often less well preserved than in the case of siliceous spicules. The forms of sponge spicules, both megascleres and microscleres, are very varied, but they can be shown to be modifications of a small number of types or fundamental forms. The spicules, on account of the constancy of their characters, are of great importance in the classification of sponges. The canal-system is indicated in the skeleton of both recent and fossil forms, by spaces in the framework of spicules or spongin, but these spaces represent only the larger canals, the smaller existing in the soft parts alone. Reproduction in the sponges takes place by budding and by the production of ova and spermatozoa. Various classifications of the sponges have been pro- 38 PORIFERA. HEXACTINELLIDA posed by different authors ; in the one adopted here the divisions are based primarily on the characters of the skeleton. Three classes are recognised, (1) Hexactinellida, (2) Demospongise, (3) Calcarea. CLASS I. HEXACTINELLIDA The spicules in the Hexactinellida (fig. 9, f) consist of three axes crossing at right angles to one another ; in primary forms there are consequently six rays of equal length proceeding from a centre. Each ray is traversed by an axial canal, and these unite at the point of junction of the six rays. Various modifications are produced by some of the rays being longer or shorter than the others, or almost absent; and also by the branching of the rays and the occurrence of spines, knobs, etc. The spicules may remain free or they may be fused with one another by a deposit of secondary silica, but they are never united by spongin. When spicules with equal rays are united end to end, skeleton-cubes are formed, each cube consisting of eight spicules (fig. 9,f). Flesh-spicules are abundant, but are seldom found fossil. Some of the spicules form a layer near the external surface of the sponge for the support of the dermal membrane ; others form a similar layer near the internal surface ; the spicules which constitute the main part of the skeleton occur in the middle of the sponge-wall and serve to support the canals and flagellated chambers. The spicules which form the root- tuft by which many Hexactinellids are fixed, are long and thread-like. The canal-system is usually simple. The earliest form is Protospongia from the Menevian Beds of St David's ; Hyalostelia is found in the Tremadoc, PORIFERA. HEXACTINELLIDA 39 and also occurs in the Ordovician, Silurian, and Car- boniferous. In the Silurian the genera Dictyophyton and Phonnosella are present. There are none in the Permian and Trias, but they become abundant in the Jurassic, especially in the upper part, and also in the Cretaceous ; they are rare in the Tertiary. Protospongia. (fig. 10.) Form unknown but probably cup- shaped. Spicules cruciform owing to the reduction of one axis, and arranged in a quadrate manner, the larger forming a framework, which contains the smaller spicules of two or three sizes, arranged in the same regular way, so that the larger squares enclose four or five series of smaller ones. The spicules were either free or probably ■A.:' Vv ^::^v%i Fig. 10. Protospongia fenestrata, Menevian Beds, St David's. x 3|. (After Hinde.) The original is in the British Museum. Owing to the cleavage of the rock the angles of the spicules are distorted. partly fused together. Menevian Beds and Lingula Flags. Ex. P. fenestrata. Craticularia. Cup-shaped or cylindrical ; simple or branch- ing. On both the inner and outer surfaces of the wall are circular or oval canal-openings, which are arranged in vertical and transverse rows crossing each other at right angles. Canals straight, terminating blindly Inferior Oolite to Upper Chalk (perhaps also Miocene). Ex. C. Jittoni, Chalk. Ventriculites. Simple, form variable, but usually cup- shaped, funnel-shaped, or cylindrical. Central cavity large and 40 PORIFERA. DEMOSPONGIiE deep. Walls folded so as to form a series of vertical grooves and ridges. Canal-system well developed ; the radial canals are large and start from the central cavity, but end before reaching the outer sur- face ; others start from the outer surface and end before reaching the central cavity. Spicules six-rayed and fused with one another so as to form a mesh-work. The node where the axes cross is hollow, having the form of a negative octahedron, the central part of each face of which is absent ; the axial canals cross in the centre of the octa- hedral space. The sponge was provided with a root consisting of siliceous fibres. Chalk. Ex. V. radiatus, V. impressus. Plocoscyphia. Sponge formed of tubes and laminae which anastomose, forming an irregular or rounded mass. Canal-system imperfect. Upper Cretaceous. Ex. P. fenestrata, Upper Greensand and Chalk Marl. CLASS II. DEMOSPONGLE The skeleton consists of siliceous spicules, or of spongin, or of both spicules and spongin. In some forms there is little or no spongin, but in others the entire skeleton consists of spongin with no siliceous spicules ; between these extremes there is a complete passage. The spicules are never of the hexactinellid type. In some few cases both spicules and 'spongin are absent. Order 1. Myxospongida. Sponges with no skeleton or occasionally with a few isolated spicules. Not known in the fossil state. Order 2. Ceratosa. Sponges with a skeleton composed of a fibrous network of spongin. This Order includes the ordinary bath sponges, etc., and is unknown in the fossil state. Order 3. Monaxonida. The skeleton is formed of spongin and spicules in varying proportions. The spicules PORIFERA. DEMOSPONGIiE 41 (fig. 9, a) consist of a single rod or axis, which may be straight or curved, and with sharp or blunt ends; each spicule may consist of two rays or of one ray only. In the former the two ends of the spicule are alike and there is a small swelling of the axial canal at the centre of the spicule where growth commenced; in the latter the two ends are dissimilar and the swelling in the axial canal is at one end of the spicule, and growth went on in one direction only. Microscleres or flesh-spicules may also occur but are often absent. Since in this Order the spicules are only united by spongin or other decomposable material, it is extremely rare to find the form of the sponge preserved fossil ; usually, detached spicules only occur. The earliest representatives of the Monaxonida are found in the Silurian ; the Order becomes more abundant in the Carboniferous, where the genus Reniera occurs. The freshwater form Spongilla is found in the Purbeck Beds of the south of England. A large number of Mon- axonid sponges are still living. Order 4. Tetractinellida. The spicules (fig. 9, b, c) consist of four rays given off from a common centre, the angle between the rays, when the end of one is taken as a central point, appearing to be 120°. The rays may be equal or unequal in length ; frequently one is very much elongated (fig. 9, c), and in such forms the three shorter rays are placed near the surface of the sponge-wall and the longer ray is directed inwards. Sometimes the termi- nations of the rays are bifurcated. Spongin is either absent or occurs in minute quantities only, and since the spicules are not united, the Tetractinellids, like the Monaxonids, are seldom preserved in anything like a perfect condition as fossils. The oldest forms occur in 42 PORIFERA. DEMOSPONGI.E the Carboniferous Limestone, where they are represented by the genera Geodites and Pachastrella. Order 5. Lithistida. The Lithistids have thick stony walls and very variable external form. The spicules (fig. 9, d, e) are stout and irregular in form, but sometimes show four rays; the extremities branch or expand, and by that means the spicules become firmly interlocked with one another, but do not fuse together. These irregular spicules (sometimes termed desmas) are formed by secondary silica being deposited on small spicules of the ordinary kind, which may be four-rayed or consist of a single axis. In addition to these irregular spicules there is generally a surface layer or cortex formed of trifid spicules like those in the Tetractinellids. Flesh-spicules are also present. Several different types of canal-system occur. The Lithistids are closely allied to the Tetracti- nellida, and are sometimes regarded as a division of that Order. Owing to their solidity the Lithistids are preserved abundantly as fossils. They are rare in the Palaeozoic; a few are found in the Upper Cambrian of Canada ; in the Ordovician and Silurian Astylospongia occurs; in the Carboniferous Doryderma, etc. No forms belonging to this Order have been found in the Devonian, Permian, or Trias ; they are numerous in the Jurassic, attain their maximum in the Cretaceous, and are scarce in the Tertiary. Verruculina. Irregular, fan- or funnel-shaped, attached by a short stalk. Oscula placed on prominent elevations on the upper, and sometimes also on the under surface. Spicules small, inter- lacing and forming a fibrous network. Ex. V. reussi, Upper Chalk. Pachinion. Cylindrical or club-shaped, tapering at its lower part to a short stem. Central cavity large and deep, with vertical PORIFERA. DEMOSPONGI.E 43 canals opening into its base. "Wall formed of anastomosing fibres, between which are irregular spaces — there are no distinct canals; fibres formed of large spicules, branched and interlaced. There is also a surface layer composed of small spicules. Chalk. Ex. P. scriptum, Upper Chalk. Scytalia. Simple, or formed of two or more individuals growing close together ; cylindrical or club-shaped, with a thick wall and a cylindrical stem. Central cavity tube-like, long, con- tinued at its base by several vertical canals ; numerous radial canals open into the central cavity and taper toward the external surface. Spicules branching, with root-like prolongations. Chalk. Ex. S. radiciformis. Seliscothon. Mushroom-like, consisting of a flat or concave, circular, plate-like body, and a rounded tapering stem. The circular body has rounded or oblique edges, and numerous, small, rounded oscula on the upper surface ; it is formed of fine vertical radiating lamella?, separated by spaces crossed by fibres — these spaces forming the canal-system. Spicules fine, branching irregularly, with bifur- cating extremities, and covered with tubercles or spines. Chalk. Ex. S. planus. Doryderma. Cylindrical, pear-shaped, sometimes branching. There are parallel vertical canals opening at the summit of the sponge, and smaller radial canals extending from the surface towards the centre. Spicules large, of various forms ; also a surface layer formed of slender trifid spicules. Carboniferous and Cretaceous. Ex. D. benetti, Upper Greensand. Siphonia. (fig. 11.) Pear-shaped, usually provided with a stalk, which is given off from the broad end of the body and termi- nates in rootlets. The incurrent canals are small, slightly curved, and extend radially from the centre of the sponge to the surface. The excurrent canals are larger, and are arranged parallel with the surface of the sponge, extending from the base to the summit, where they open into the large central cavity by means of a series of parallel ostia. The skeletal-spicules possess four rays with bifurcated and expanded extremities, by means of which they are interlocked. Upper Greensand to Upper Chalk. Ex. S. tulipa, Upper Green- sand. 44 PORIFERA. DEMOSPONGI.E Hallirhoa. Like Siphonia but with the sides divided into lobes. Upper Greensand. Ex. H. costata. Order 6. Octactinellida. The spicules (fig. 9, g), consist of eight rays, six of which are in one plane diverging at equal angles, while the other two are at right angles to this plane, forming a vertical axis. Frequently, however, the vertical axis is only slightly developed or altogether absent. The spicules are not united. The only genus is Astrcvospongia, found in the Silurian and Devonian. i— B Fig. 11. Siphonia tulipa. Upper Greensand, Warminster. A, vertical section. B, horizontal section, e, excurrent canals ; i, incurrent canals, x £, Order 7. Heteractinellida. The spicules are un- usually large (fig. 9, h), the number of rays varying from six to thirty. The body spicules are not fused, but there is a surface layer in which the spicules are interwoven and more or less fused. The only genera are Tholiasterella and Aster actinella, found in the Carboniferous rocks of Ayrshire. PORIFERA. CALCAREA 45 CLASS III. CALCAREA (CaLCISPONGIjE) The skeleton consists of spicules composed of carbonate of lime in the condition of calcite. The spicules are usually much smaller and less varied in form (fig. 9, j) than those of the siliceous sponges, and cannot be separated into megascleres and microscleres. There are three kinds, the simple uniaxial, the three-rayed, and the four-rayed ; they are sometimes fused with one another, but often are either arranged close together so as to form fibres, or are loosely distributed. Spongin is never present. The earliest British forms of the Calcarea occur in the Carboniferous rocks of Fifeshire. Peronidella. Cylindrical, simple or branched ; central cavity tubular and extending from the summit to the base of the sponge. Walls thick and with no definite canals, but having irregular spaces between the spicular fibres. Spicules three- or four-rayed, forming anastomosing fibres. Carboniferous (possibly also Devonian) to Cretaceous ; most abundant in the Jurassic and Cretaceous. Ex. P. pistilliformis, Great Oolite and Cornbrash. Corynella. Form similar to Peronidella. Radial excurrent canals open into the central cavity, which often does not extend to the base of the sponge, but is continued downwards by vertical canals. Incurrent canals fine, directed obliquely downward. Osculum usually with radial furrows. Jurassic and Cretaceous (? Trias). Ex. C. foraminosa, Lower Greensand. Holcospongia. Simple or compound :• individuals usually spherical, hemispherical, or club-shaped ; their summits rounded, with a central area in which a number of excurrent canals open, and from which furrows extend down the sides of the sponge. Spicules large and three-rayed, and some also filiform ; and a surface layer of three-rayed spicules, of various sizes, felted together. Inferior Oolite to Cretaceous. Ex. H. polita, Corallian. 46 PORIFERA. CALCAREA Rhaphidonema. Cup- or funnel-shaped or leaf-like, usually with definite canals. Oscula on either the inner or the outer surface. Spicules of three rays, one of which is but slightly developed. On one (or sometimes both) surfaces is a thin, compact or finely porous layer of spicules. Trias to Cretaceous. Ex. R. macropora, Lower Greensand. Barroisia. Usually compound and bushy. Individuals cy- lindrical, each divided into a series of chambers by transverse partitions, which have a central circular opening, through which a tube usually passes. Canals simple, numerous, minute. Spicules slender, three-rayed ; also a surface layer of larger spicules. Lower Greensand to Chalk. Ex. B. anastomans, Lower Greensand. PorosphaBra. Small simple sponges, commonly more or less spherical, but sometimes pear-, thimble-, or melon-shaped ; often free, but sometimes attached to foreign bodies. Numerous, simple, straight, radiating canals open at the surface by minute apertures. Spicules with four rays, of which three are short and blunt and fused to the rays of adjoining spicules, whilst the fourth ray is longer and tapering. A surface layer (not often preserved) consists of a mixture of minute three- and four-rayed spicules and simple rods. Upper Cretaceous. Ex. P. globularis, Chalk. Distribution of the Porifera. The Sponges are all aquatic, and with the exception of the Monaxonid genus Spongilla and its allies, all marine. They are found in the seas of all parts of the world and are more numerous between the shore-line and 200 fathoms than at greater depths; many of the genera have a very wide distribution. All the Orders except the Octac- tinellida and the Heteractinellida have living repre- sentatives. The Monaxonids are abundant between the shore-line and 200 fathoms, and gradually decrease in TORIFERA 47 numbers beyond that limit. The Tetractinellids are also common in water of less depth than 200 fathoms, but extend down to 2000 fathoms. The Lithistids range from 7J to 1075 fathoms, and are most abundant between 100 and 150 fathoms. The Hexactinellids occur in deeper water than the Lithistids, being found down to a depth of 2900 fathoms ; but they are abundant between 100 and 200 fathoms, and again between 300 and 700 fathoms. The Calcarea are mainly shallow water forms. The fossil forms are comparatively rare in the Palaeozoic rocks until we reach the Carboniferous; and throughout the geological formations they are much less abundant in argillaceous than in calcareous and arenaceous rocks. Sponges are first found in the Lower Cambrian rocks ; the earliest British form is Protospongia from the Menevian Beds and Lingula Flags ; in the Tremadoc the Hexacti- nellid genus Hyalostelia occurs, ranging onwards as far as the Chalk. In the Ordovician we have in the Llandeilo Beds the first appearance of Ischadites1, associated with Hyalostelia ; in the Bala Beds we meet with Astylospongia. The most abundant Silurian form is Ischadites; Astraso- spongia, Phormosella, and Hyalostelia also occur. Sponges are rare in the Devonian, but Astrceospongia, Sphcero- spongia\ and Receptaculites1 have been recorded. In the Carboniferous rocks, sponges become much more common, the siliceous spicules often forming thick beds of chert : the Monaxonids are represented by Reniera, the Tetracti- nellids by Geodites, the Lithistids by Doryderma, the 1 The sponge-character of the Silurian and Devonian genera Ischadites, Receptaculites, and Sphcerospongia, which have been placed by some authors in the Hexactinellida, is now disputed ; if they are sponges it is probable that they belong to the Calcarea, since their skeleton appears to have consisted originally of carbonate of lime. 48 PORIFERA Hexactinellids by Hyalostelia, and the Heteractinellids by Tholiasterella and Asteractinella. Sponges appear to be absent in the Permian ; and they are rare in the Trias, except in the St Cassian Beds of the Tyrol, where the Calcarea are numerous. In the Jurassic, sponges are extremely abundant ; the only Monaxonid is Spongilla from the Purbeck Beds ; Lithistids and Hexactinellids although common in Ger- many and Switzerland are comparatively rare in England ; the first group is represented by Platychonia, the second by Craticularia, Verrucoccelia, etc. ; the Calcarea are numerous in this country as well as in France and Ger- many, common genera being Peronidella, Corynella, and Holcospongia. The occurrence of Hexactinellids in the Inferior Oolite is noteworthy, since other evidence shows that that deposit was laid down in shallow water, but at the present day Hexactinellids are characteristic of deep water. Sponges are more abundant in the Cretaceous than in any other system ; in England they are found chiefly at four horizons : — (1) in the Lower Greensand of Faringdon, Up ware, Kent, and Surrey, where the Calcarea are much better represented than the other groups, Peronidella, Barroisia, and Rhaphidonema being common forms : (2) in the Upper Greensand and Chloritic Marl of War- minster, Blackdown, Haldon, and the Isle of Wight, where the Lithistids {e.g. Dory derma, Siphonia, Hallirhoa) are very abundant, exceeding the Hexactinellids {e.g. Craticu- laria, Plocoscyphia, Stauronema) ; the Calcarea are also common in places : (3) in the Lower Chalk of the south of England, where we find Siphonia, Craticularia, Stauro- nema, Plocoscyphia, etc. ; the Calcarea are rare : (4) in the Upper Chalk, where the siliceous sponges are very PORIFERA 49 common ; amongst the Lithistids the following occur : — Seliscothon, Verruculina, Scytalia,Doryderma,8ind Siphonia; the Hexactinellids are represented by Graticularia, Verru- coccelia, Guettardia, Ventriculites, Cephcdites, Plocoscyphia, and Camerospongia; the Calcarea are represented by Porosphcera. In the Tertiary formations detached spicules are sometimes abundant, but few perfect sponges have been found. w. p. PHYLUM CCELENTEKA Classes 1. Hydrozoa 2. Scyphozoa (Scyphomedusae) 3. Anthozoa or Actinozoa 4. Ctenophora (not fossil). . Orders 1. Gymnoblastea. 2. Calyptoblastea. 3. Graptolitoidea. 4. Hydrocorallina. 5. Stromatoporoidea. 6. Trachomedusae (not fossil). 7. Narcomedusae (not fossil). 8. Siphonophora (not fossil). 1. Stauromedusaa (not fossil). 2. Peromedus83 (not fossil). 3. Cubomedusae (not fossil). 4. Discomedusas. 1. Zoantharia. 2. Alcyonaria, The Coelentera include hydro-ids, jelly-fishes, sea-anemones, corals, and allied forms. The individuals are radially symmetrical, and have only one internal cavity, the cceleiiteron, which opens to the exterior by the mouth. The body-wall consists of an outer layer of cells, the ecto- derm, and an inner layer, the endoderm ; between these is a gelatinous layer — usually quite thin, but in the jelly- fishes of considerable thickness. Stinging cells known as nematocysts or thread-cells are generally present in the ectoderm. The canal-system, so characteristic of the sponges, is absent. HYDROZOA 51 This Phylum is divided into four classes, (1) Hydro- zoa, (2) Scyphozoa or Acalephse, (3) Anthozoa or Actinozoa, (4) Ctenophora. CLASS I. HYDROZOA The simplest type of the Hydrozoa is the common freshwater Hydra. In this the body has the form of an elongated sac, about a quarter of an inch in length, and is attached by one end, whilst at the other is the mouth surrounded by a row of long processes, called tentacles. The large undivided cavity in this sac, which opens into the hollow tentacles above, is the ccelenteron. The whole body is very contractile and constantly changing its shape. Reproduction may take place in three ways, (1) by the growth of buds, which ultimately separate from the parent, (2) sexually, by the production of ova and spermatozoa in the ectoderm, and (3), in rare cases, by fission. Other Hydrozoa consist of a number of individuals (polyps or hydranths) similar to Hydra, but growing together as a colony (fig. 12); all the individuals in such cases are placed in living communication by means of a tube-like extension from the base of each polyp ; this common connecting portion of the colony is called the camosarc (fig. 12, 5). Frequently the coenosarc is much branched, giving rise to tree-like forms; it is usually attached to some foreign object by a horizontal branching portion. In such hydroid colonies the polyps are asexual, and the reproductive elements are produced in another in- dividual of a somewhat different character, known as a medusa or gonophore: this arises by budding from the hydroid (fig. 12, 9), and is often more or less bell-shaped, 4—2 52 HYDROZOA and may become detached from the colony, or it may be less perfectly developed and remain attached ; at the inner edge of the bell is a shelf-like fold, the velum. The generative cells are of ectodermal origin, and from them the hydroid develops. Hydra possesses no hard parts, but in other forms an external skeleton composed of chitin or of carbonate of lime is secreted ; it commonly forms a tube-like sheath around the coenosarc and is called the perisarc (fig. 12, 6). In one group the perisarc is produced at the base of each polyp into a cup-like structure or hydrotheca (fig. 12, 7), into which the polyp can retract. The gonophores may also be protected by a chitinous capsule called the gonotheca or gonangium (fig. 12, 10). The vertical branch- ing part of the coenosarc together with the perisarc around it, is called the hydrocaulus ; the horizontal root- like portion and its perisarc form the hydrorhiza. The principal characters which distinguish the Hydrozoa from the other Coelenterates are : the coelenteron being undivided by radial partitions or ridges ; the absence of a digestive tract projecting into the coelenteron; the usual occurrence of an asexual (hydroid) generation alternating with a sexual (medusoid) generation ; the medusa having a velum ; the ova and spermatozoa being derived from the ectoderm. Nearly all the Hydrozoa are marine. They are divided into eight Orders, of which five occur fossil: — (1) Gymno- blastea, (2) Calyptoblastea, (3) Graptolitoidea, (4) Hydro- corallina, (5) Stromatoporoidea. ORDER I. GYMNOBLASTEA The Gymnoblastea have no hydrothecse into which the polyps can retract ; gonangia (gonothecse) are also absent. HYDROZOA. GYMNOBLASTEA 53 Well-known living forms are Tubularia, Bougainvillea, and Hydr actinia. The last has been found fossil in Eocene and later deposits ; it forms a crust over the shells of gasteropods, especially those tenanted by Hermit- crabs. The hard part of this crust is chitinous, or rarely calcareous, and consists of laminae separated by irregular or cubical spaces and crossed by vertical pillars ; on the surface are projecting spines. The soft parts form a layer over this skeleton, and consist of a sheet of ecto- derm on the surface, and another sheet next the skeleton ; between these are branching and anastomosing coenosarcal tubes. The skeleton is secreted by the lower ectoderm. From the ccenosarc arise the polyps, which are placed on long vertical stalks and are of four kinds, (1) gastrozooids — the ordinary nutritive individuals, (2) blastostyles, which are individuals specially modified for bearing medusae, (3) dactylozooids — individuals modified for catching prey and having short knob-like tentacles crowded with nemato- cysts, (4) tentacular polyps, which are very slender, with- out a mouth, and occur near the edge of the colony. Parkeria, which is found in the Cambridge Greensand, probably belongs to this Order. A few other forms have been described from the Alpine Trias and the Jurassic of southern Europe. A. ORDER II. CALYPTOBLASTEA This Order is distinguished by the presence of hydro- thecae and gonangia (gonothecae). (Fig. 12, 7, 10.) The arrangement of the polyps and hydrothecse on the hydrocaulus varies considerably in different genera. Some- times they are placed on stalks as in Obelia (fig. 12) and Campanularia\ in many others they are sessile. They 54 HYDROZOA. CALYPTOBLASTEA — 10 --- 9 .-8 Fig. 12. Part of a branch of Obelia. Enlarged. To the left a portion is shown in section. (After Parker and Haswell.) 1, ectoderm ; 2, endoderm ; 3, mouth ; 4, coelenteron ; 5, ccenosarc ; 6, perisarc ; 7, hydrotheca ; 8, blastostyle, a mouthless polyp bearing medusa- buds ; 9, medusa bud ; 10, gonangium or gonotheca. HYDROZOA. CALYPTOBLASTEA 55 may be in rows or placed in various positions on the hydrocaulus. In Plumularia, Aglaophenia, etc., they form a single row ; in Sertularia, etc. there are two rows placed on opposite sides of the branches. Sometimes the hydrothecse are close together, but more usually they are separated. In the Plumulariidse there are, in addition to the ordinary polyps, others which are solid and tentacle-like ; they are usually provided with nematocysts and are called nematophores ; each one is placed in a hydrotheca. Although the Calyptoblastea possess a well-developed chitinous skeleton, yet, with the exception of a form found in the Pleistocene, they are not definitely known to occur as fossils. In the Lower Palaeozoic, however, there are organisms (usually termed 'dendroid graptolites ') which present considerable resemblance to the Calyptoblastic hydroids ; the best known are Dendrograptus, Ptilo- graptus, Dictyonema, and Callograptus. These are usually much branched and tree-like, and are fixed by a root-like structure ; hydrothecse occur, but no virgula is found. Transverse sections of Dictyonema and Dendrograptus show that some of the branches consist of a group of tubes of various sizes, somewhat resembling in this respect the recent forms Clathrozoon and Grammaria. Dictyonema (= Dictyograptus) is found in the Cam- brian, Ordovician, and Silurian, and has a fan- or funnel- shaped skeleton which consists of numerous radiating branches, placed nearly parallel with one another, and united by transverse fibres. Dendrograptus occurs in the Ordovician, Callograptus in the Arenig, and Ptilograptus ranges from the Arenig to the Ludlow Beds. 56 HYDROZOA. GRAPTOLITOIDEA ORDER III. GRAPTOLITOIDEA The graptolites are found only in the Lower Palaeozoic rocks, where, owing to their abundance and to the limited range in time of both genera and species, combined with their wide geographical distribution, they are of great importance to the stratigraphical geologist. They occur most commonly in argillaceous rocks, especially in black shales, whilst they are rare in sandstones and limestones. The graptolites resemble the Calyptoblastea, e.g. Sertu- laria and Plumidaria; they were compound animals, and the soft parts were protected by a skeleton of chitin. But the original material of the skeleton is seldom preserved unaltered ; in some cases it has been replaced by iron pyrites, but usually it has become carbonised. The entire skeleton (exclusive of the soft parts) is termed the polypary; this in an unbranched form like Monograptus consists of a tubular part known as the common canal (fig. 13 b, c), which extends nearly the whole length of the animal, the wall being termed the periderm or perisarc. From one side of the common canal small tooth-like projections are given off; these are the hydrothecod (fig. 13 b, h), each of which is hollow and opens on the one hand into the common canal and on the other to the exterior ; the latter aperture, known as the mouth (m) of the hydrotheca, is frequently circular, but sometimes quadrangular or slit-like. Embedded in the periderm on the side opposite to the row of hydrothecaB is a chitinous thread or rod, termed the virgida (fig. 13 b, a). In some species of Monograptus the virgula projects HYDROZOA. GRAPTOLITOIDEA 57 beyond the distal1 end of the common canal. At the proximal end of the polypary there is a small conical body, termed the sicula (fig. 13, c, s), which will be described more fully below (p. 61). The soft parts of the graptolites are of course unknown, but from comparison with living hydroids which have a similar skeleton, we may consider it probable that each hydrotheca lodged an individual polyp, and that these were connected by means of the ccenosarc which occupied the common canal. a <= IYb - — k i a. ■S Fig. 13. a, Portion of Monograptus personatus ; b, diagrammatic vertical section of the same ; c, Monograptus colonus, Coniston Grits, with sicula (s) ; d, Diplograptus foliaceus, LlandeiloBeds, with virgula (a), and the position of the embedded sicula (s) indicated. All enlarged. a, position of virgula in wall of b ; c, common canal ; h, hydrotheca ; m, mouth of hydrotheca; s, sicula. In the form just described {Monograptus) the polypary is always simple, but in many genera it consists of two or more branches or stipes. When there are several 1 The proximal end is that which in recent hydroids is attached ; the distal is the free end. In the graptolites the proximal end is formed first, the distal end last. The side of the graptolite on which the hydro- thecaa occur is spoken of as the ventral, and the opposite side as the dorsal. 58 HYDROZOA. GRAPTOLITOIDEA radiating branches their proximal parts are sometimes enclosed in a horny sheath, termed the central disc, as in some species of Tetragraptus (fig. 14). In those genera which have two branches (fig. 17), the angle between the two is termed the angle of divergence ; it is measured from the hydrothecal side of the dorsal wall of each branch. In some cases {e.g. Monograptus, fig. 13 c) the polypary possesses only a single row of hydrothecse, such forms are said to be uniserial; others (e.g. Diplograptus, fig. 13 d) possess two rows on opposite sides of the polypary — these are the biserial forms, and they may have a single common Fig. 14. Tetragraptus headi, Arenig Rocks, a, central disc, x i. canal as in Retiolites, or there may be two canals separated by a septum, as in Climacograptus : in many forms of Diplograptus there is only one common canal, but others possess an incomplete septum which, to some extent, divides the canal into two parts. In Dicranograptus the proximal part of the polypary is biserial, whilst the distal part consists of two uniserial branches. In Dimorpho- graptus, on the other hand, the proximal part is uniserial and the distal part biserial ; this genus therefore serves to connect Diplograptus and Monograptus. The hydrothecse vary considerably in form in different HYDROZOA. GRAPTOLITOIDEA 59 genera, and sometimes even in different species of the same genus; but in any one species they are usually similar, except that they diminish in size towards the proximal end of the polypary; they may resemble the sicula in shape (Didymograptus), or they may be tubular {Rastrites), prismatic (Diplograptus), conical (Monograptus tricing ulatus), or coiled {Monograptus lobiferus). They may be in contact throughout their entire length (Phyllo- gvaptus), at their bases only (Nemagraptus), or, in a few cases, entirely separate (Rastrites). Frequently they are provided with one or more spines _.-w near the mouth. In most grapto- lites the hydrothecse communicate freely with the common canal, and in this respect differ from living hydroids, in which there is a constriction or an imperfect dia- phragm at the base of each hydrotheca, separating it from the common canal (fig. 12); but some specimens of Didymograptus and Tetragraptus seem to show evi- dence of a septum between each hydrotheca and the common canal. A microscopic examination of thin sections of Monograptu s shows that the periderm consists of three or four layers, the external and internal layers being much thinner than the others. In Retiolites the middle layer of the periderm is formed of a network of fibres (fig. 15) whilst the inner and outer layers are very thin. B w-' x Fig. 15. Retiolites geinitzi, Silurian. A, section across polypary. B, proximal end of polypary with the outer layer removed. Enlarged (after Holm). ?c, .r, rods in the network formerly re- garded as virgulae. 60 HYDROZOA. GRAPTOLITOIDEA In the uniserial genera the virgula, when present, is placed in the periderm opposite the row of hydrothecae, but in the biserial forms it is central, being situated either in the middle of the common canal, as in some forms of Diplograptus, or in the septum separating the two canals, as in Climacograptus. In several genera (Didymograptus, Phyllograptus, Tetragraptus, Dichograptus, Dicellograptus) the virgula is not found in the wall of the common canal, but projects as a thread from the pointed end of the sicula. The position of the sicula varies in different genera. In Monograptus it is united to the dorsal surface of the polypary, the pointed end being . directed distally (fig. 13 c, s). In Diplograptus it has a similar position but is more or less completely enclosed between the hydrothecae (fig. 13 d, s). In Didymograptus its broad end only is united to the two branches of the polypary, the pointed end being directed proximally (fig. 17, s). In Dicellograptus it projects like a spine between the two branches. The appearance of even the same species of graptolite varies considerably according to its mode of preservation. Frequently it is flattened to a film, and when this is the case we may get a side view, a front view showing the mouths of the hydrothecae, or a back view; in the two latter cases the margins will be parallel. But when the original material has been replaced by iron pyrites, or when the graptolite is preserved in a limestone, the natural form of the polypary is often retained. No medusoid form is known in the graptolites; but, in one respect, their mode of reproduction appears to have been similar to that which takes place in some living Hydrozoa. In a few biserial graptolites (fig. 16) sac-like bodies have been found attached to the polypary ; these, HYDROZOA. GRAPTOLITOIDEA 61 when perfect, are pear-shaped, and resemble the gonangia of living Calyptoblastea (see fig. 12, 10); they are not joined to the hydrothecse, but come off at right angles to them along the middle line of the sides of the polypary. The earliest condition of the graptolite at present known is the sicula (fig. 18 A) ; this probably is developed within the sac-like bodies if they are, as suggested, really gonangia. Fig. 17. Fig. 16. Fig. 16. Diplograptus with sacs resembling gonangia. (After Hall.) Natural size. Fig. 17. Didymograptus v-fractus, Arenig Beds. Early part of the polypary. (After Elles.) s, sicula ; c, crossing-canal ; 1, first hydro- theca ; 2, second hydrotheca. x 5. The mode of development of graptolites has been studied in several genera. The sicula is usually more or less clearly exposed at the proximal end of the polypary (fig. 13 c) ; it is a hollow cone (fig. 18 A) open at the base, and consists of two parts — the pointed or apical end with 62 HYDROZOA. GRAPTOLITOIDEA a thin wall (b), and the broader or apertural part with a thick wall marked with lines of growth (a). The pointed part was probably the covering of the embryo, and the broad part a later growth. The apical end of the sicula is prolonged as a thread forming the virgula. A spine- like projection is sometimes found at the apertural end Fig. 18. Early stages of Monograptus and Diplograptus (after Wiman). Enlarged. A. Sicula of Monograptus, from the Silurian of Gothland, a, thick- walled part with lines of growth ; b, the earliest part with a thin wall ; c, spine-like projection from the apertural end of the sicula. Monograptus (same locality) with three hydrothecae developed. 1, 2, 3, first, second, and third hydrothecffi ; a, b, sicula ; c, spine-like projection ; d, virgula. Diplograptus from Bornholm, with four hydrothecffi developed. 1, 2, 3, 4, first, second, third, and fourth hydrothecae ; a, sicula. B C of the sicula (fig. 18 A, c), but has no connection with the virgula. In the development of Didymograptus a bud is formed on one side of the sicula and from this arise HYDROZOA. GRAPTOLITOIDEA 63 (1) the first hydrotheca (fig. 17, l) and (2) a tubular body known as the crossing-canal (c); the latter grows across the sicula and gives rise to the second hydrotheca (2) which is on the side opposite to the first hydrotheca. From each of these two hydrotheca? a stipe or branch is developed, owing to the fact that each hydrotheca gives rise by budding to another hydrotheca and in this way two continuous linear series are formed. More complex branching (as in Tetragraptus, Dichograptus) is produced when one hydrotheca buds off two hydrotheca? instead of one. In Diplograptus (fig. 18 C) the development is similar to that of Didymograptus but the crossing-canal is reduced in size and the hydrothecse grow up the virgula instead of in the direction of the apertural end of the sicula ; also the hydrothecse are budded off on either side alternately, so that the second hydrotheca (2) is on the side opposite to the first (1), and the third (3), which is budded from the second, is on the same side as the first and overlies it. This alternate arrangement may continue throughout the development of the polypary, but frequently a septum appears between the two rows of hydrotheca?, and thenceforward each hydrotheca arises from the pre- ceding one on the same side. In Monograptus the hydrotheca? (fig. 18 B) arise on one side only of the sicula. Owing to the fact that the soft parts of the graptolites are entirely unknown it is difficult to speak of their affinities with any degree of certainty. It seems probable, however, that they belong to the Hydrozoa ; Allman and others consider them to be closely related to the Calypto- blastea, especially to such forms as Sertularia and Plumu- laria, with which they agree in the general characters of the hydrotheca? and common canal, and perhaps also in the possession of gonangia. But they differ in some 64 HYDROZOA. GRAPTOLITOIDEA important respects from the Calyptoblastea, e.g. in possess- ing a virgula and sicula, in the diminution in size of the hydrothecae towards the proximal end of the polypary, in the hydrothecae being nearly always in contact, and in the free communication which exists in most cases between the hydrothecae and the common canal ; their development is also different — in the graptolites each hydrotheca is budded off from another hydrotheca, but in the Calypto- blastea the new polyps are budded off from the ccenosarc. Fig. 19. Diplograptus pristis, from the Utica Slate, New York. V 2 X -3-. (After Ruedemann.) Further, the graptolites never form the much-branched tree-like colonies which occur so commonly in recent hydroids, and the graptolites are never firmly fixed by any root-like structure corresponding to the hydrorhiza. Some authors have considered that the graptolites were free-swimming animals ; but it is very probable that some, at any rate, were attached to sea-weeds or other foreign objects by means of the virgula which, in some genera comes off as a free thread from the point of HYDROZOA. GRAPTOLITOIDEA 65 the sicula {e.g. Didymograptus) ; if they were fixed to floating sea-weeds their wide geographical distribution would be readily accounted for. Ruedemann has described specimens of Diplograptus pristis (fig. 19), from the Utica Slate (Ordovician) of New York, which consist of a number of individuals radiating from a centre where they unite by the distal prolongations of their virgulas ; at the point of union there is a small, nearly square, chitinous sheath which is similar in appearance to the central disc of Tetragraptns ; below this is a larger quadrate body, apparently vesicular, which was at first regarded as a float or pneumatocyst, but later as probably an organ of fixation at the base of the colony. Around the small disc are from four to eight globular vesicles, which Ruedemann considers to be gonangia, since they contain siculse; the siculae sometimes pass out and develop into fresh colonies, but in other cases they remain attached to the parent, and, by the growth of the virgula, extend outwards, and subsequently hydrothecse arise in the usual way. In some other species of Diplograptus {D. vesicidosus, etc.) a single vesicle is sometimes found attached to the distal end of the virgula. The genera of graptolites at present accepted are based, to a large extent, on the number of branches of the polypary ; but Nicholson and Marr consider that this feature is of less importance than was formerly supposed, and that a classification which shows the genealogical relationships of the forms should be founded chiefly on the characters of the hydrothecse and, to some extent, on the angle of divergence of the branches. The early grapto- lites, such as Bryograptus, appear, at first sight, to be more advanced than the later types {e.g. Monograptus), on account of their more complex branching ; but in the w. p. 5 66 HYDROZOA. GRAPTOLITOIDEA early forms the hydrothecse are very simple, differing but little from the sicula, whereas in the later ones they exhibit considerable modification. In some genera the hydrothecse of different species show great variety of form, those of one species being often much more like those of a species belonging to another genus than to other species of the same genus : thus we get the same type of hydrotheca in the three forms Bryograptus cal- lavei, Tetragraptus hicksi, and Didymograptus affinis, and another type in Bryograptus retroflexus, Tetragraptus denticidatus, and Didymograptus fasciculatus. It is con- tended that each of these groups is a genealogical series and should be regarded as a genus — that T. hicksi has descended from B. callavei, and D. affinis from T. hicksi. According to the old view all the species of Didymograptus were thought to have descended from one common ancestor; but this will not account for the close resemblance which the hydrothecse of certain species of Didymograptus bear to those of certain species of Tetragraptus] on the other hand, this is readily explained if we consider that the species of Didymograptus have descended from various species of Tetragraptus. Then again, the remarkable diversity in the hydrothecse of Monograptus can be easily understood if we grant that the forms included under this term are the descendants of different species of one or more genera. But since species which have a different ancestry cannot be placed in the same genus, we must regard Monograptus as an assemblage of forms which agree merely in consisting of a single uniserial branch or stipe. It has been suggested that the similar modification in branching found in different forms may have been brought about by the necessity of obtaining sufficient food — the HYDROZOA. GRAPTOLITOIDEA 67 larger the number of branches the smaller would be the total supply of food for each individual of a colony ; conse- quently, when one species of a four-branched type {Tetra- graptus) had become a two-branched form, it would have a considerable advantage over the remaining four-branched forms, which would, as a result, soon die out. Didymograptus. (fig. 17.) Polypary bilaterally sym- metrical, consisting of two uniserial stipes diverging at an angle which varies, in different species, from 0° to 180° (or occasionally more). Hydrothecse subcylindrical, in contact for a considerable part of their length. Lower Arenig to Upper Llandeilo. Ex. D. murchisoni, Lower Llandeilo ; D. patuhis, Arenig. Phyllograptus. (fig. 20.) Polypary leaf-like, consisting of four uniserial stipes united along the whole of their length. Hydrothecae cylindrical or subcylindrical, in con- tact throughout their entire length. Sicula pointing distally. Arenig. Ex. P. typus. Tetragraptus. (fig. 14.) Poly- pary bilaterally symmetrical, uni- serial, consisting of four simple radi- ating branches which arise from the bifurcation of two short branches coming off from opposite sides of the sicula (constituting a Didymograptus stage). Hydrothecae cylindrical or subcylindrical, in contact for a considerable part of their length. A central disc may or may not be present. Arenig. Ex. T. quadri- brachiatus. Dichograptus. Polypary typically bilaterally symmetrical consisting of eight uniserial main stipes produced by bifurcation through Didymograptus and Tetragraptus stages. Hydrothecae cylindrical or subcylindrical. A central disc is frequently present. Lower Arenig. Ex. D. octobrachiatus. Loganograptus (Arenig) and Clonograptus (Tremadoc and Arenig) are forms in which bifurcation has proceeded further than in Dicho- graptus. 5—2 Fig. 20. Phyllograptus, Arenig Rocks. The polypary has been cut in two, and the upper part raised so as to show the four branches. Natural size. 68 HYDROZOA. GRAPTOLITOIDEA Bryograptus. Polypary bilaterally symmetrical, uniserial, consisting of two main stipes diverging at a small angle from the sicula, which has its point directed distally. From the inner margins of the main stipes similar secondary stipes (which may bear other stipes) arise. Hydrothecse like those of Dichograptus. Tremadoc. Ex. B. kjerulfi. Leptograptus. Polypary consisting of two simple, slender, flexuous, uniserial stipes given off in opposite directions from the sicula at angles greater than 180°. Hydrothecae are long tubes with slight sigmoid curvature, in contact for half their length. Upper Llandeilo to Lower Bala. Ex. L. Jlaccidus, Lower Bala. Pleurograptus. Two principal branches as in Leptograptus; these bear secondary branches on both sides, often arising alter- nately, and sometimes bearing smaller branches. Lower Bala. Ex. P. linearis. Nemagraptus ( = Ccenograptus). Polypary bilaterally sym- metrical, uniserial, consisting of twro slender, more or less flexuous main stipes coming off from the middle of a well-defined sicula ; from each of these stipes secondary branches may be given off in a symmetrical or nearly symmetrical manner. Hydrothecse as in Leptograptus. Llandeilo. Ex. N. gracilis. DicranograptUS. Polypary bilaterally symmetrical, biserial in the proximal portion, dividing distally into two uniserial branches. Hydrothecse with sigmoid curvature and inturned apertures. Upper Llandeilo to Lower Bala. Ex. D. clingani, Bala. DicellograptUS. Like Dicranograptus, but uniserial through- out, the two branches united at the sicula only, which points distally. Angle of divergence greater than 180°. Upper Arenig to Upper Bala. Ex. D. anceps, Upper Bala. DiplograptUS. (fig. 13 d.) Polypary biserial. Hydrothecse subprismatic or subcylindrical, overlapping and placed obliquely. Virgula prolonged beyond the distal extremity of the polypary. Sicula more or less completely concealed. Lower Arenig to Tarannon. Ex. D. foliaceus, Llandeilo to Lower Bala. Petalo- graptus and Cephalograptus are sub-genera ; Llandovery and Tarannon. HYDROZOA. GRAPTOLITOIDEA 69 Climacograptus. Polypary biserial. Hydrothecse tubular, with sigmoid curvature, apertures placed in depressions. Sicula often concealed. Upper Arenig to Tarannon. Ex. C. normalis, Llandovery and Tarannon. Dimorphograptus (see p. 58). Llandovery. Monograptus. (fig. 13 c.) Polypary unbranched, uniserial ; straight, curved, or spiral. Hydrothecse vary in form in different species. Sicula attached to the proximal end of the polypary, and its j)ointed end directed distally. Lower Llandovery to Lower Ludlow. Ex. M. nilssoni, Lower Ludlow ; M. leptotheca, Llandovery ; M. priodon, Wenlock ; M. spinigerus, Llandovery. Rastrites. Similar to Monograptus, but the hydrothecse are long, tubular, and widely separated. Llandovery to Tarannon. Ex. R. peregrinus, Llandovery to Tarannon. CyrtOgraptUS. Similar to Monograptus, but coiled into a plane spiral with branches given off from the external (hydrothecal) margin. Upper Tarannon to Lower Ludlow. Ex. G. murchisoni, Wenlock Shale. Retiolites. (fig. 15.) Polypary biserial, straight. Hydrothecae like those of Diplograptus. Periderm consists mainly of a network of threads and rods. Lower Bala to Wenlock. Ex. R. geinitzianus, Upper Tarannon and Wenlock. Distribution of the Graptolitoidea In Britain the earliest graptolites occur in the Tremadoc Beds, where we find the genera Bryograptus and Clono- graptus ; in the Olenus-shales of West Gothland Dicho- graptus also occurs. The last two forms are also present in the lower part of the Arenig Beds, but other genera such as Tetragraptus and Diclymograptus are associated with them and soon become abundant ; Phyllograptus also occurs here. In the Llandeilo, the graptolites are transi- tional between the Arenig and Bala forms, Phyllograptus is absent, Didymograptus is fairly common in the lower 70 HYDROZOA. GRAPTOLITOIDEA part, and the genera Nemagraptus, Dicellograptus, Dicrano- graptus, Diplograptus and Climacograptus now appear for the first time. In the Bala Beds, the four last-mentioned genera become much more abundant, and with them occur Leptograptus and Pleurograptus. The only genera which pass up from the Bala to the Silurian are Climacograptus, Diplograptus, and Retiolites ; not a single Bala species (except perhaps a variety of Climacograptus scalaris) is found in the Llandovery Beds, so that between the Ordovician and Silurian there is a great break in the graptolitic succession. As a whole, the Silurian formations are characterised by the presence of the genera Mono- graptus, Rastrites and Cyrtograptus, which appear first at the base of the Llandovery Beds. In the lower part of the Llandovery the genera Diplograptus and Climaco- graptus are fairly abundant, but they become extinct in the Tarannon, and in the Wenlock and Ludlow Beds the only forms are Monograptus, Cyrtograptus, and Retiolites. The last traces of graptolites occur in the Downtonian Beds, but they are too imperfect for determination. ORDER IV. HYDROCORALLINA The skeleton in the Hydrocorallina is calcareous and has the form of encrusting or branching masses. It con- sists of a network of rods, in which there are tubes of two sizes opening on the surface ; the larger are called gastropores, and have horizontal partitions or tabulae ; the smaller are named dactylopores. The skeleton is of ecto- dermal origin, and is secreted by a network of coenosarcal tubes, above which is a superficial layer of ectoderm. The polvps project above this layer, and are of two kinds : nutritive individuals or gastrozooids, which are placed in HYDROZOA. HYDROCORALLINA 71 the gastropores, and dactylozooids placed in the dactylo- pores. Millepora is an important rock-building organism at the present day, often contributing largely to the forma- tion of coral-reefs ; it has been recorded from Cainozoic deposits, but whether these examples really belong to that genus appears to be somewhat doubtful. Stylaster is a living form, and is stated to occur in the Miocene. Milleporidium from the Upper Jurassic of Stramberg and Millestroma from the Upper Cretaceous of Egypt may belong to this Order. ORDER V. STROMATOPOROIDEA In the Stromatoporoids the skeleton is calcareous1, and very variable in form ; it may be hemispherical, spheroidal, dendroid, encrusting, or altogether irregular, and frequently forms large masses. It consists of a series of concentric laminae separated by spaces ; these are crossed at right angles by rods or pillars, which give off horizontal pro- cesses at definite intervals; these processes join together and really form the laminae. The under surface of the skeleton is often covered by a thin imperforate layer, with concentric furrows, similar to the epitheca of many com- pound corals. On the upper surfaces of the laminae there are, in many forms, shallow grooves, having a stellate arrangement, and known as astrorhizce. In some genera, as for example Actinostroma (fig. 21), the two elements of the skeleton, the laminae and pillars, remain quite distinct, but in others, like Stromatopora, they become to a great extent blended together so as to form a more or 1 In some specimens the carbonate of lime has been dissolved and its place taken by silica. 72 HYDROZOA. STROMATOPOROIDEA less netted structure ; between these two types, however, there are intermediate forms. The first type (Actino- stroma) is similar to Hydractinia (see p. 53), but is always calcareous and forms larger masses ; the second (Sfrornato- pora) resembles Millepora (see p. 71), and, like that genus, possesses tubes with horizontal partitions, but the tubes seem to be of one size only, and consequently there is nothing to indicate that this type was dimorphic; it differs also in possessing radial pillars. c D Fig. 21. A, Tangential section of Actinostroma intertextum showing the radial pillars. B, vertical section showing the radial pillars and the formation of the concentric laminse by processes given off from these, x 12. C and D, parts of A and B further enlarged. From the Silurian Rocks. (After Nicholson.) The soft parts in the Stromatoporoids probably formed a continuous layer on the surface of the skeleton, and the polyps in some cases (e.g. Stromatopora) were placed in HYDROZOA. STROMATOPOROIDEA 73 definite tubes, but in others tubes are absent and there are pores only in the external lamina. From the structure of the skeleton, the Stromatoporoids seem to be connected with both Hydr -actinia and the Hydrocorallina. • The Stromatoporoids are found mainly in the Ordo- vician, Silurian, and Devonian Systems, being most abundant in the last ; frequently they are of considerable importance as rock-builders; some of the best known genera are Labechia, Stromatopora, Stromatoporella, Actinostroma, Clathrodictyon, Idiostroma, and Amphipora. A few specimens, which are believed to be Stromatoporoids, have been found in deposits of Mesozoic age. CLASS II. SCYPHOZOA The Scyphozoa (Scyphomedusse) or Acalephse include the larger and more conspicuous jelly-fishes, such as Aurelia, Rhizostoma, and Pelagia. They possess no hard parts; nevertheless the impressions of some forms {e.g. Rhizostomites) belonging to the Order Discomedusse have been found in the Lithographic Limestone (Upper Jurassic) of Solenhofen in Bavaria. Even in the oldest fossiliferous formations traces of supposed Scyphozoa have been found; the most satisfactory of these is the form from the Lower Cambrian of Sweden referred to the Discomedusse, and named Medusina costata ( = Medusites lindstroemi). Others, but of which the nature appears to be somewhat doubtful, have been described by Walcott from the Middle Cambrian of Alabama. 74 ANTHOZOA CLASS III ANTHOZOA (ACTINOZOA) This Class includes the corals and sea-anemones. They differ from the Hydrozoa (1) in possessing an oeso- phageal tube, which is distinct from the ccelenteron, though opening into it ; (2) in having the ccelenteron divided up into chambers by vertical radiating partitions known as mesenteries ; (3) in the reproductive elements being developed in the endoderm of the mesenteries and never on a medusa. .- 11 Fig. 22. Semi-diagrammatic view of half a simple Coral. (Partly after Bourne.) On the right side the tissues are represented as trans- parent to show the arrangement of the theca and septa ; on the left a mesentery is seen. 1, tentacle; 2, mouth; 3, stomodaeum ; 4, mesentery ; 5, mesenteric filaments, free edge of mesentery ; 6, ectoderm ; 7, endoderm ; 8, basal plate of skeleton ; 9, theca ; 10, columella ; 11, septum. The Anthozoa possess an apparent radial symmetry, but closer examination reveals a bilateral arrangement ANTHOZOA 75 of their parts. In a typical form, such as the common sea-anemone or a simple coral (fig. 22), the body has a more or less cylindrical shape, and is attached by one end, the other having an opening, the mouth (fig. 22, 2), surrounded by tentacles (l). The mouth leads into the oesophageal tube or stomodceum (3), which opens at its lower end into the coelenteron. The latter is divided into chambers by radiating partitions, the mesenteries (fig. 22, 4 and fig. 23 a — c), each of which consists of a thin gelatinous layer in the middle and a layer of endoderm on each side. In the upper part of the polyp the inner edges of the principal mesenteries join the stomodseum, but in the lower part they remain free, and a section in the former region (fig. 23) will show the body wall and also the stomodaBum, but in the latter the body wall only. The tentacles (fig. 22, 1) are placed immediately above the intermesenteric chambers, and the space in each tentacle is continuous with that of the chamber below. A bilateral symmetry is indicated by the oval or slit-like mouth, and the similarly compressed stomodaBum ; also by the arrange- ment of the longitudinal muscles which occur on one face of each mesentery, extending from the base of the polyp upwards (fig. 23). The sea-anemones have no hard parts, but the majority of Anthozoa possess a skeleton, which in many cases is quite external to the body, and is formed of carbonate of lime (fig. 22, 8, 9) ; in others it is internal and may consist of calcareous spicules, or of an axial rod of horny or calcareous material. The Anthozoa are divided into two Orders, (1) the Zoantharia, (2) the Alcyonaria. 76 ANTHOZOA. ZOANTHARIA ORDER I. ZOANTHARIA In the Zoantharia the tentacles are generally numerous and are never eight in number, as is the case in the Alcyonaria ; occasionally there are six only, but frequently a multiple of six, and they usually form several circles around the mouth. The tentacles are nearly always simple (fig. 22, 1). The mesenteries (fig. 23, a, b, c) are usually numerous also, and form several cycles ; those belonging to the primary cycle are formed first and reach to the stomodseum ; the other cycles (secondary, tertiary, etc.) are successively smaller. The mesenteries are arranged d e Fig. 23. Diagrammatic section of a Zoantharian polyp passing through the stomodasum. a, primary mesenteries ; b, secondary mesenteries; c, tertiary mesenteries ; d, e, primary mesenteries at the ends of the compressed stornodseum. The muscles are indicated by the thicken- ings on the mesenteries. in couples (fig. 23) with the longitudinal muscles of each couple facing one another, except in the case of the couples situated at the grooved ends of the stomodseum, where the muscles are turned away from each other (d, e). A skeleton is often present and may be calcareous or horny ; when calcareous it is never composed of spicules but con- sists of aragonite fibres. ANTHOZOA. ZOANTHARIA 77 The Zoantharia comprise, (1) the sea-anemones, which have usually been grouped together as the Actinaria, and are unknown in the fossil state, since they possess no hard parts; (2) the Antipatharia — colonial forms in which the skeleton consists of an internal horny rod secreted by the ectoderm ; these also are not found fossil ; (3) the Madre- poraria, including the well-known stony corals, which are very abundant as fossils. MADREPORARIA The polyp of a Madreporarian coral has essentially the same structure as a common sea-anemone, but the ecto- derm of the lower part of the body secretes a skeleton consisting of carbonate of lime (fig. 22, 8, 9). The entire skeleton is spoken of as the corallum, and in compound corals the skeleton of each individual is termed a corallite. The parts of the skeleton may be solid, or they may be perforated, or formed of a network of rods. In a typical simple coral (fig. 25) the skeleton has a more or less conical form ; the base of the cone, on which the jt£\ 1 l/^< polyp is placed, is usually de- ^\\ ' /^a pressed, and is termed the calyx. L^ _nt--- — J-c The wall bounding the corallum a \^^/ 1 Vvi is known as the theca (fig. 22, 9; >£'/ \ I \^^~ fig. 24, d) ; sometimes there is, *> ' ^*4-L>^ outside this, another calcareous Fig; 24; Diagrammatic sec- tion (horizontal) 01 a simple layer, the epitheca. The whole coral, a, columella ; b, pri- space enclosed by the theca is nTss^ments^115 f/'theCa; termed the visceral chamber) it is divided up by various partitions, the most important of which are the septa (fig. 22, 11 ; fig. 24, b). These are 78 ANTHOZOA. ZOANTHARIA vertical plates extending from the theca towards the centre, and alternating in position with the mesenteries. The septa are of different sizes, some reaching the centre, others being shorter ; they frequently occur in series or cycles, of which three or more may often be distinguished, the largest being the primary (b), the others the secondary, tertiary, etc. In many corals found in the Palaeozoic formations one of the primary septa (the cardinal septum) is much smaller than those formed after it, and consequently appears, at the surface of the calyx, to lie in a pit or cavity, which is called a fossula (figs. 33 a, 34 A, a). Usually only one fossula is present — the cardinal fossula, but sometimes another, known as the counter fossula (fig. 34 A, dd) occurs on the opposite side of the coral, and less commonly two others (e) called alar fossula} are present one on each side of the coral. When the septa project upwards above the edge of the theca they are said to be exsert (fig. 25). The faces of the septa are sometimes plane, but usually bear ridges, granules, or spines. In some corals the septa are poorly de- veloped, and may be represented by ridges only or by rows of spines. In the centre of the visceral chamber, where the Fig. 25. Montlivaltia trochoides, t , , . «, Inferior Oolite, showing exsert larger septa meet, there is often septa. x i. a vertical rod, which extends from the base of the chamber to the bottom of the calyx ; this is the columella (figs. 24 a ; 31 c). Its structure varies considerably ; when it is solid and ends in a knob or point in the calyx, it is said to be styliform ; sometimes the top is porous or spongy. When the columella consists ANTHOZOA. ZOANTHARIA 79 of twisted laminae it is termed trabeculate ; if formed by the twisting together of processes given off from the inner edges of the septa, it is false : in some genera there is no columella. Other vertical partitions, somewhat similar to the septa, are the pali (fig. 24 c) ; these are radiating plates attached to the columella and placed opposite the inner edges of some of the shorter septa, but not joining them. Bars or rods, known as synapticulce, are often found passing from one septum to another. Similarly, adjacent septa are often connected by plates, which may be horizontal or oblique, straight or curved, and are called dissepiments (figs. 24 e ; 31 d) ; in some genera they are very abundant near the margin of the visceral chamber and form a spongy or vesicular tissue (fig. 30 d). Lastly we have the tabular (figs. 30 t; 31 B, t), which are more or less horizontal plates, crossing the septa, and occupying the central part of the visceral chamber, or, when well developed, extending quite across it; they are arranged one above another, so that the visceral chamber is divided into horizontal compartments. On the outside of the wall of the coral there are, in some forms, vertical ridges, which may be smooth or spiny ; these are known as costaz, and usually correspond in position with the septa. The young coral polyp is a free-swimming animal; when it becomes fixed the first part of the skeleton to appear is a circular plate between the base of the polyp and the surface to which it is attached ; on this plate radial ridges — the first traces of the septa — are secreted in folds formed in the base of the polyp between the mesenteries. The theca next appears at the edge of the plate, and is formed either by the union of the ends of the septa, or as an independent structure. For some time the polyp ex- tends down to the base of the cup-like skeleton (fig. 22) 80 ANTHOZOA. ZOANTHAR1A and a fold hangs over the outside (fig. 22, 6, 7); but as the septa, theca, etc., increase in height the lower part of the visceral chamber (in most cases) becomes more or less completely cut off by the development of dissepiments or tabulae, below which the soft parts do not extend. As growth proceeds more of these partitions are formed, and eventually a large part of the coral ceases to have any direct connexion with the polyp. Some corals remain simple (i.e. consist of a single individual throughout life). Others, which are simple in the young state, afterwards become compound and form Fig. 26. A. Dendrophyllia nigrescens, showing corallites which have heen produced by lateral budding. Recent, x \. B. Cyathophyllum truncatum, showing calicular budding, Wenlock Limestone. Natural size. C. Cladochonus crassus (seen from above), showing basal budding, Carboniferous Limestone. Natural size. colonies, either by giving off buds, or by fission. In budding, new individuals may arise from the part of the polyp which extends outside the theca (fig. 22, 6, 7), in which case a branching coral like Dendrophyllia (fig. 26 A) is frequently formed ; this mode of increase is termed lateral budding. In other cases buds arise on the upper surface of the old polyp, and then the young corallites are ANTHOZOA. ZOANTHARIA 81 found inside the calyx of the parent — hence this is known as calicular budding (fig. 26 B). In basal budding (fig. 26 C), which is rare in the Madreporaria but common in the Alcyonaria, the buds spring from creeping prolonga- tions or stolons, which are given off from the base of the coral. Fission, or division into halves, commences by the mouth becoming slightly constricted in the middle ; this increases until two distinct mouths and two polyps are formed, after which a similar division takes place in the Fig. 27. Section of a dissepiment of Galaxea. Magnified, g, growth- lamellas. (From M. M. Ogilvie.) skeleton. When the individual corallites in a compound form are free and diverge from one another, the corallum is termed dendroid (fig. 26 A) : when they are in contact, it is massive. If the corallites are not in contact the spaces between the individual corallites are sometimes filled up with calcareous material formed by the coenosarc, and known as coenenchyma. In many compound corals (e.g. Acervularia) the base of the corallum is covered by a thin epithecal plate — the basal epitheca. In dendroid corals (fig. 26 A) the polyps on the different corallites may be quite separate from one another ; but in massive corals, whilst the upper parts of the polyps are w. p. ,. o 82 ANTHOZOA. ZOANTHARIA more or less separate, the lower parts are united. When coenenchyma is present the polyps are united by an ex- tension of the part which ordinarily occurs outside the theca, and now forms a sheet called the coenosarc. Microscopic examination of thin sections shows that each part of a coral is formed of thin layers or growth- lamellae which consist of fine needle-like crystals placed Fig. 28. Transverse section of part of a septum and theea of Galaxea. Highly magnified, d, dark spots ; g, growth- lamelhe; a, granule on septum. (From M. M. Ogilvie.) more or less perpendicularly to the surfaces of the lamellae. In a section of a dissepiment (fig. 27) a series of lines parallel to the surface and other finer lines crossing at right angles are seen — the former mark the growth- lamellae, the latter the crystalline fibres. In a transverse section of a septum (fig. 28) there is a median dark line or row of dark spots, on each side of which the structure is symmetrical. When the surface of the septum is plane, ANTHOZOA. ZOANTHARIA 83 the lamellae are straight, or nearly straight, and parallel with the surface, and the fibres are perpendicular ; but when the surface is ridged the lamellae are curved so as to be parallel with the ridges, and the fibres radiate out from the dark median spots toward the curved surface of the ridge (fig. 28). When the septa bear striae, granules, or spines, in addition to ridges, the folding of the lamellae and the radiating arrangement of the fibres become more complex ; but in all cases the structure is directly related to the form of the surface. The dark lines and spots represent the part of the septum which was first secreted ; their dark appearance may be due either to the less regular arrangement of the fibres or to the imperfect calcification of the material of that part. In fossil corals the dark part has often undergone secondary changes which give it a more distinct appearance. In the development of a living Zoantharian coral six primary septa are first formed and appear simultaneously ; next, six secondary septa are introduced between the primary septa ; other cycles may subsequently be added in a somewhat similar manner, so that in the adult the septa have generally a completely radial arrangement. In the Rugose corals of the Palaeozoic period the development1 of the septa follows a different course. Instead of the six primary septa appearing simultaneously, two septa (fig. 29 A), one on each side, are first formed and meet in the centre of the coral — representing the cardinal (l) and counter septa (l') of the adult, on the ventral and dorsal sides respectively (fig. 34 A, a, b) ; next, two more septa (fig. 29 B, 2) appear, one on each side of the cardinal 1 This can be studied by gradually grinding down the tip of a perfect specimen. The arrangement of the septa in Rugose corals can also be seen either on the surface of the wall or by removing the theca. 6—2 84 ANTHOZOA. ZOANTHARIA septum, and as growth proceeds these become more widely separated from the cardinal septum, and eventually form the alar septa of the adult (fig. 34 c) ; afterwards, two septa (3) are added, one on each side of the counter septum, and these also spread outwards as growth proceeds (as indicated by the arrows in fig. 29 D). The six septa now present are regarded as the primary septa (1, 2, 3). The later ® C 3, -3 b l b Fig. 29. Development of the septa in a simple Eugose Coral, Zaphrentis. 1 — 3, primary septa; 1, cardinal septum; 1' counter septum; 2, alar septa; 3, counter-lateral septa; a, b, c, later septa (metasepta). (After Carruthers.) septa (sometimes termed metasepta) are introduced in pairs ; these appear at four points — one septum on each side of the cardinal septum (1), and one between each alar septum (2) and the primary septum (3). The two pairs which are first added (fig. 29 E, a) are attached to the cardinal sides of the primary septa 2 and 3 ; similarly later pairs (fig. 29 F, G, b, c) ANTHOZOA. ZOANTHAMA 85 are introduced and are joined to the cardinal sides of the previously formed septa. As growth proceeds all the later septa (a — c), unlike the primary septa, gradually move towards the counter septum, as indicated by the arrows in fig. 29 G. In the adults of some Rugose corals (fig. 34 A) the arrangement of the septa is similar to that just described, so that on each side of the cardinal fossula and on the counter side of each alar septum the later septa (metasepta) have a pinnate arrangement. In other genera, however, the pinnate plan is not seen in the adult (figs. 32, 33), since all the septa either become free at their inner edges or unite only at the centre of the coral ; and in such cases, unless a fossula is present, the symmetry of the coral is nearly or quite radial. From the description of the septal development given above, it will be seen that the fossulse are breaks in the sequence of the septa. The cardinal fossula (fig. 34 A, a) is limited by the later septa added on each side of the small cardinal septum. The counter fossula, on the opposite side, where no new septa are introduced, is bounded by the two primary septa (d, d) which enclose the counter septum (6). The alar fossulse are the spaces between each alar septum (c) and the newer septa which have been added on its counter side. The fossilise have been regarded as pits or chambers for those mesenteries which alone were specialised for repro- duction. Another explanation of the nature of the cardinal fossula is that it is due to the presence of a groove on the ventral side only of the stomodaeum, similar to that found in the living family Zoanthidse ; it is thought that such a groove would account for the small size of the cardinal septum. 86 ANTHOZOA. ZOANTHARIA By many authors the Madreporarian corals have been divided into three sections: (1) the Aporosa, (2) the Perforata, and (3) the Rugosa. The characters of these groups are : — (1) Aporosa. Theca and septa solid, the latter generally in multiples of six, with usually six primary septa. Tabulae rare. (2) Perforata. Distinguished from the Aporosa by the septa and theca being perforate. The perforations are sometimes numerous, so that the skeleton appears to consist of a network of rods. (3) Rugosa. Septa and theca solid, tabulae well developed. The coral is usually bilaterally symmetrical owing to the arrangement of the septa on either side of two opposite primary septa (the cardinal and counter septa), and to the presence of one or more fossulae. When four fossulae are present a tetrameral character is given to the coral. The Rugosa are almost limited to the Palaeozoic formations ; the name of the group is taken from the vertical ridges often seen on the wall of the coral. It is doubtful if this classification can be maintained. The separation of the Aporosa from the Perforata is especially difficult, since some of the former possess a few perforations in the septa, whilst the latter occasionally have nearly compact septa. Until recently it has been generally maintained that the Rugosa possess only four primary septa — the cardinal, the counter, and two alar septa, which divide the coral into quadrants ; on account of this the name Tetracoralla has sometimes been used for this group. The study of the development of the septa has shown that there are really six primary septa, and the Rugose corals consequently ANTHOZOA. ZOANTHARIA 87 agree in that respect with living Madreporaria, so that it is probable that both have descended from the same ancestors; the difference in the mode of development of the later septa, however, seems to indicate that the two groups soon diverged. If this view is correct then the Rugosa must be regarded as a natural division. Other writers, however, maintain that the Rugose corals do not form a natural group, since the bilateral symmetry, the fossulse, etc., which were regarded as characteristics, are not in all cases found in adult specimens ; and further, some of the Mesozoic genera of Aporose corals are stated to possess fossulae and a bilateral symmetry, and to show in the young stages a pinnate arrangement of septa like that found in Rugose corals. Also some of the families of Aporose corals, particularly those found in the Trias and Jurassic, are said to possess features similar to those of certain Rugose families of the Palaeozoic period, from which it is inferred that they are the descendants of the latter. Thus, for example, the Astraeidae (Aporosa) are believed by some authors to be closely related to the Cyatho- phyllidae (Rugosa), and the Turbinolidae (Aporosa) to the Zaphrentidae (Rugosa). If this view of the affinities of Aporose and Rugose families is correct, it is obvious that the Rugosa cannot be regarded as a natural group which became extinct or nearly extinct at the close of the Palaeozoic period, but that different Rugose families are the ancestors from which a number of Aporose families have sprung independently. Until more is known of the affinities of the Rugose corals it will be convenient to divide the genera described in the following pages into Rugose, Aporose, and Perforate groups. 88 ANTHOZOA. ZOANTHARIA 1. Rugose Corals. Cyathophyllum. (fig. 30.) Simple or compound massive. Septa numerous, of two sizes, alternating, the longer reaching the centre where they may give rise to a false columella. Fossula often absent. Tabulae rather small, occupying the central part only of the visceral chamber. Dissepiments form an extensive peripheral zone of vesicular tissue. Bala to Car- boniferous. Ex. C. murchisoni, C. regium, Carboniferous Lime- stone. often Fig. 30. Cyathophyllum murchisoni, Carboniferous Limestone. Por- tion of a vertical section, d, dissepiments ; t, tabulae. Acervularia. Compound, massive ; corallites with an outer polygonal (frequently hexagonal) theca, and an inner circular wall formed by the thickening of the septa. Septa well developed, the longer reaching the centre. Columella absent. Tabulae extend across the central part of the visceral chamber. Dissepiments form a peripheral zone of vesicular tissue. Silurian to Devonian. Ex. A. ananas, Silurian. A B Fig. 31. Lithostrotion basaltiforme, Carboniferous Limestone. A. Hori- zontal section of a single corallite, x 2J. B. Vertical section, x 5. c, columella ; t, tabulae ; d, dissepiments ; w, theca. Phillipsastraea (=Smitkia). Compound, massive. Septa numerous, with oblique ridges : septa of adjacent corallites con- ANTHOZOA. ZOANTHARIA 89 fluent. Theca thin or indistinct. No columella. Tabulae and dissepiments well developed. Devonian and Carboniferous. Ex. P. hennahi and P. pengellyi, Devonian ; P. radiata, Carboniferous. Lithostrotion. (fig. 31.) Compound, either massive and with prismatic corallites, or formed of separated, nearly parallel, cylindrical corallites. Septa well developed, alternately long and short. Columella rod-like, laterally compressed. Peripheral zone of dissepiments narrow. Tabulae wide, occupying the centre of the visceral chamber. Fossula often distinct. Carboniferous. Ex. L. basaltiforme. Omphyma. Simple, turbinate or conical. Septa numerous, alternately long and short, but extending only a short distance into the visceral chamber, the central part being occupied by tabulae. Four shallow fossulae are present. No columella. Peripheral zone of dissepiments relatively narrow. The theca gives off root-like processes. Bala to Lower Ludlow. Ex. 0. subturbinata, Wenlock Limestone. a Fig. 32. Fig. 33. Fig. 32. Cli stop hy Hum bipartitum, Carboniferous Limestone. Horizontal section showing the large central 'pseudo-colurnella.' Natural size. Fig. 33. Cyclophyllum fungites, Carboniferous Limestone. Horizontal section, a, cardinal fossula. x 1^. Clisiophyllum. (fig. 32.) Simple, turbinate or subcylindrical. Septa numerous, alternately long and short ; a well-marked cardinal fossula. In the centre of the visceral chamber is a large ' pseudo- 90 ANTHOZOA. ZOANTHARIA columella,' which consists of vertical radiating plates crossed obliquely by vesicular tabula? ; this structure forms a prominent projection at the bottom of the calyx. The pseudo-columella is surrounded by a zone formed of tabulae, and external to this is a large zone of dissepiments. Carboniferous. Ex. C. bipartitum. Dibunophyllum. Like Clisiophyllum but with a strong median vertical plate across the pseudo-columella. Carboniferous. Ex. D. muirheadi. Cyclophyllum. (fig. 33.) Like Clisiophyllum but with pseudo-columella surrounded by a distinct wall which is produced on one side into an angular or tongue-like projection pointing towards the fossula. Carboniferous. Ex. C. fungites. Fig. 34. Zaphrentis delanouei, Carboniferous Limestone. A, horizontal section ; a, cardinal septum in fossula ; b, counter septum ; c, alar septa ; d, counter-lateral septa bounding the counter fossula ; e, alar fossula. B, vertical section showing tabulas bending down into the cardinal fossula (a) ; b, counter side. x 5. Drawn by R. G. Carruthers. Lonsdaleia. Similar to Clisiophyllum, but compound, and the septa do not reach the wall of the corallite, the marginal part being occupied by dissepiments only. Carboniferous. Ex. L. duplicata. Cyathaxonia. Simple, turbinate or elongate-conical. Septa reach the columella, which is solid. Fossula present. Tabula? sometimes present. No dissepiments. Carboniferous. Ex. C. cornu. Zaphrentis. (fig. 34.) Simple, free, bilateral ; turbinate, conical, or cylindrical, often curved ; calyx deep ; theca thick. A well- ANTHOZOA. ZOANTHARIA 91 marked cardinal fossula is present. Septa moderately numerous, the larger reaching very nearly or quite to the centre, the smaller usually short. Tabulae well developed, extending quite across the visceral chamber. No true dissepiments. Columella absent. Silurian to Carboniferous. Ex. Z. delajiouez, Carboniferous Limestone. Amplexus. Similar to Zaphrentis, but generally cylindrical, and with very short septa. Devonian and Carboniferous. Ex. A. coralloides, Carboniferous. Caninia. Form similar to Zaphrejitis, but often cylindrical and slender. The longer septa meet in the centre in the lower part of the coral, but are usually short in the upper part. No columella. Tabulae well developed. A peripheral ring of more or less vertical dissepiments is present in the adult part. Carboniferous. Ex. C. cormtcopice. A B ill m Fig. 35. Calceola sandalina, from the Middle Devonian ; A, showing interior of calyx; B, inside of operculum of the same. Natural size. Streptelasma. Simple, conical or turbinate, bilateral, with a thick wall. Septa numerous, alternately long and short. A fossula usually present, but sometimes indistinct or wanting. Columella large, false, trabeculate. Tabulae irregular, usually poorly developed. Dissepiments moderately developed. Ordovician and Silurian. Ex. S. comictdum, Ordovician. Cy stiphy Hum . Nearly always simple, conical. Septa and tabulae absent or rudimentary ; visceral chamber filled with vesicular tissue, the outer part consisting of dissepiments, the central part representing tabulae. Fossula sometimes present. Columella absent. Calyx often deep, commonly with ridges representing septa. Silurian and Devonian. Ex. C. vesiculosum, Devonian. Calceola. (fig. 35.) Simple, conical or slipper-shaped, one side is flat, the other convex ; calyx very deep and closed by a semilunar 92 ANTHOZOA. ZOANTHARIA operculum, which has on its inner surface a strongly -marked median ridge and several less prominent lateral ridges ; septa indicated by striae in the calyx ; wall thick. Middle Devonian. Ex. C. sandalina. Goniophyllum. Similar to Calceola, but quadrangular ; operculum consists of four plates forming a pyramid over calyx. Visceral chamber filled with vesicular tissue. Silurian. Ex. G. Jletcheri, Wenlock Limestone. An operculum also occurs in the allied genus Rhizophyllum, Silurian. 2. Aporose Corals. Turbinolia. Simple, conical, free ; calyx circular, with pro- jecting columella. Septa exsert. Costse lamellar, projecting, with pits in the grooves between them. No dissepiments or tabulse. Eocene and Oligocene (? Recent). Ex. T. humilis, Barton Beds. Flabellum. Simple, compressed, fan-shaped, free or fixed by rootlets. Calyx narrow, deep ; septa numerous. Columella trabe- culate. Costae smooth or spiny. Upper Cretaceous to present day. Ex. F. woodi, Coralline Crag. Montlivaltia. (fig. 25.) Simple, fixed or free ; turbinate, cylindrical, conical, or discoidal. Epitheca well developed, theca thin. Columella absent. Septa numerous, strong, often exsert, the upper edges dentate. Dissepiments abundant. Trias to Recent ; in England, Lias to Corallian. Ex. M. trochoides, Inferior and Great Oolite. Parasmilia. Simple, fixed, turbinate or elongate. Calyx circular. Columella spongy. Septa well developed, exsert, granular on the sides. Wall with costse. Cretaceous to present day. Ex. P. centralis, Chalk. IsastraBa. Compound, massive ; calyces polygonal. Walls of the corallites fused along their entire length. Columella rudi- mentary or absent. Septa thin and close together. Dissepiments abundant. Trias to Eocene; in England, Lias to Upper Greensand. Ex. /. explanata, Corallian. Stylina. Compound, usually massive ; calyces circular, pro- jecting, usually separated. Columella small, styliform. Septa exsert. Dissepiments abundant. Corallites united by costse. Basal epi- ANTHOZOA. ZOANTHARIA 93 theca with folds. Trias to Cretaceous ; in England, Inferior Oolite to Corallian. Ex. S. tubulifera, Corallian. Thecosmilia. Compound, dendroid or rarely almost massive. Multiplication by fission. Margins of calyces irregular. Columella rudimentary or absent. Septa strong, upper edges dentate, more or less exsert. Dissepiments abundant. Epitheca thick and folded, but often not preserved. Trias to Tertiary ; in England, Lias to Kimeridgian. Ex. T. annularis, Corallian and Kimeridgian. Holocystis. Compound, massive, convex ; calyces polygonal. Columella very small or absent. Corallites united by their walls or by costse. The four principal septa are much better developed than the others. Tabulse well developed. Lower Greensand. Ex. H. elegans. 3. Perforate Corals. Thamnastraea. Compound, massive ; convex or laminar. Walls of the corallites indistinct. Calyces shallow. Septa formed of fan-shaped rows of rods ; the septa of adjoining corallites con- fluent ; faces of septa with granulations. Columella small, trabe- culate. Dissepiments present, synapticulse numerous. Usually a basal epitheca. Trias to Miocene ; in England, Lias to Upper Greensand. Ex. T. arachnoides, Corallian. Micrabacia. Simple, free, discoidal, base concave. Colu- mella false. Septa numerous, with their outer edges perpendicular. Synapticulse present. Theca on the base only, thin ; costse granular. Upper Cretaceous. Ex. M. coronula. G-oniopora ( = Litharcea). Compound, massive. Calyces more or less polygonal. Septa well developed, the faces spiny, the upper edges dentate. Walls of the corallites reticulate. Columella formed by the ends of the septa. Cretaceous to present day, common in the Eocene. Ex. G. websteri, Bracklesham Beds. ORDER II. ALCYONA.RIA The Alcyonaria are nearly all colonial organisms ; the polyps possess eight mesenteries and eight tentacles, the latter being provided with pinnules (fig. 36, 4). In the 94 ANTHOZOA. ALCYONARIA stomodgeum there is only one groove with cilia, and the longitudinal muscles on the mesenteries are all directed toward the groove (fig. 37, 6). All the mesenteries reach the stomodseum (l). The nature of the skeleton varies Considerably ; in A Icyonium it consists of isolated spicules of carbonate of lime embedded in the common gelatinous iff #?#i — 4 If lor Fig. 36. Part of a colony of Alcyonium digitatum, showing thirteen polyps in various stages of retraction and expansion. (From Shipley and MacBride.) 1, mouth; 2, stomodasum; 3, mesenteries; 4, ten- tacles, x 8. base in which the polyps are placed. In some cases it has the form of an axial rod surrounded by the soft parts ; this rod may consist of horny material (e.g. Gorgonia) or of car- bonate of lime (e.g. Corallium, the red coral), or it may be formed of alternating segments of horny and of calcareous material as in Isis. In the ' organ-pipe coral ' (Tubipora ANTHOZOA. ALCYONARIA 95 musica, fig. 38) the skeleton consists of numerous parallel tubes or corallites (a) which are not in contact but are held together by horizontal calcareous plates or ' plat- forms ' (b). The walls of the corallites, although apparently quite compact, are really composed of spicules which have serrated edges and are firmly fitted together. A single Fig. 37. Transverse section through a polyp of Alcyonium digitatum in the region of the stomodaeum. x about 120. 1, cavity of stomodasum ; 2, ventral groove with cilia (siphonoglyph) ; 3, ectoderm ; 4, gelatin- ous layer; 5, endoderm; 6, muscles of mesenteries; 7, cavity between mesenteries. (After Hickson.) polyp lives at the summit of each corallite ; spicules occur in the middle gelatinous layer of the polyp, and in the lower part become interlocked to form the solid wall of the corallite. The interior of each corallite is divided up by tabulae which are often funnel-shaped (fig. 38 c). 96 ANTHOZOA. ALCYONARIA In some of the Alcyonaria, as for example Pennatula, there are in addition to the ordinary polyps (or autozooids) others of a more rudimentary character, known as siphono- zooids, in which tentacles are absent. The blue coral (Heliopora) differs from other living Alcyonaria in that the skeleton consists of calcareous fibres instead of spicules, and in this respect resembles the Madreporaria. Heliopora has the form of branched or lobed masses, and is composed of tubes of two sizes ; the a --.£> »*-<#$ Fig. 38. Tubipora musica, Recent. A, part of a colony, natural size. B, diagrammatic vertical section of one corallite (enlarged) showing canals in the wall and platform, a, corallite; b, platform; c, tabula. larger tubes or corallites are circular and possess usually fifteen spine-like projections at their summits with ridges below ; these are called pseudosepta, since they are not related to the number of mesenteries and do not corre- spond with true septa. The smaller tubes form a coenenchyma between the corallites, and are more irregular in form. Both corallites and coenenchymal tubes are divided by horizontal plates or tabulae. The soft parts form a thin sheet over the surface of the skeleton ; polyps ANTHOZOA. ALCYONARIA 9' (fig. 39, ab) are placed in the corallites and give off branching tubes (d) which cover the coenenchyma and send blind prolongations or caeca (e) into its tubes. The caeca were formerly regarded as siphonozooids. Fig. 39. Heliopora carulea. A single polyp and the adjacent soft parts. a, the projecting part of the polyp with eight pinnate tentacles ; b, lower part of the polyp ; c, ectoderm; d, sheet of canals; e, caeca. (After Bourne.) Alcyonaria are rare as fossils, unless the Palaeozoic genera, described below, be included in that group; but the systematic position of those genera cannot yet be regarded as definitely established. Some of them present considerable resemblance to living Alcyonaria ; for example, Si/ringopora is similar to Tubipora, and Heliolites to Heliopora : on account of this, many authors maintain that these fossil forms belong to the Alcyonaria, but this relationship is denied by other writers who point out that the skeleton is not formed of spicules, but is similar in structure to that of Zoantharian corals, and further that there is a close resemblance between Favosites and the 7 w. p 98 ANTHOZOA living Zoantharian A Iveopora ; if it could be shown that these two forms are related, then it would follow that Favosites and other allied fossil genera (including Syringo- pora) must be placed in the Zoantharia. Another view of these Palaeozoic corals is that they do not belong to either the Zoantharia or the Alcyonaria, but constitute an isolated group of the Anthozoa. These genera are characterized by their numerous and well-developed tabulae, and by the septa being, in most cases, represented by ridges or spines only. A few species which appear to be allied to the Palaeozoic forms have been found in deposits of Mesozoic age. Syringopora. Compound ; corallites tubular, for the most part not in contact, more or less parallel to one another. The interiors of the different corallites communicate by means of horizontal connecting tubes. Septa feebly developed, generally represented by spines. Tabulae numerous, more or less funnel-shaped. Budding basal. Llandovery to Carboniferous Limestone. Ex. S. reticulata. Carboniferous. Syringopora agrees with Tubipora (fig. 38) in consisting of parallel, cylindrical corallites, which have funnel-shaped tabulae, and in its basal-budding ; it differs from Tubipora in having much thicker walls which are not composed of spicules, and are not per- forated by minute canals ; also in the tabulae being much less regular in form and position, and in possessing septa in the form of spines. The platforms of Tubipora (which are traversed by canals opening into the corallites) are represented by the connecting tubes of Syringopora ; in one species of Syringopora (S. tabulata) the resemblance is particularly close, since the connecting tubes are given off from the corallites at definite levels in a radiating manner. On the other hand it must be noted that ITeterocosnia provincialis, an Aporose coral from the Chalk, closely resembles Tubipora in its general build. Favosites. Compound, massive, sometimes branched. Coral- lites long and polygonal ; the walls are in contact but not fused, and are perforated by pores ('mural pores') arranged in rows along each ANTHOZOA 99 face. Septa absent or represented by rows of spines. Tabulae numerous, regular, generally extending quite across the visceral chamber. Basal epitheca present. Bala to Carboniferous Lime- stone. Ex. F. gothlandica, Silurian. Favosites is related to Syringopora, but the corallites are in contact, and consequently connecting tubes are absent, though probably represented by the mural pores. The living Madreporarian Alveopora agrees in general structure with Favosites, but its walls are less compact, and its basal epitheca is quite small. Some corals (e.g. Koninckia, Ubaghsia) which resemble Favosites are found in the Upper Cretaceous, and are regarded by some writers as links between Favosites and Alveopora. Alveopora has been recorded from the Upper Cretaceous of Portugal. Pachypora. Similar to Favosites, but the walls of the coral- lites are greatly thickened, especially near the surface of the coral, by a secondary deposit of carbonate of lime. Silurian to Carboni- ferous. Ex. P. cervicornis, Devonian. Alveolites. Allied to Favosites. Massive, encrusting, or branching. Corallites laterally compressed, with thin walls and large mural pores. Silurian and Devonian. Ex. A. labeckei, Silurian. Pleurodictyum. Compound, discoidal, attached by part of the base, upper surface slightly convex. Corallites diverge from the centre of the base ; walls thick, with irregular pores. Septa rudi- mentary. Tabula? not numerous, more or less united. A basal epitheca. Silurian and Devonian. Ex. P. problematicum, Devonian. XVXichelinia. Similar to Pleurodictyum, but the tabula? are more numerous and form a vesicular tissue, and root-like processes are usually given off from the epitheca on the base of the coral. Devonian and Carboniferous. Ex. M. favosa, Carboniferous. Heliolites (fig. 40). Corallum compound, massive or branch- ing, formed of tubes of two sizes ; the larger circular ones are the corallites, between which are the smaller polygonal tubes forming the ccenenchyma. Tabulae occur in both, and in the corallites there are septa which are usually lamellar and are generally twelve in 7—2 100 ANTHOZOA number. Columella sometimes found in the corallites. Bala to Devonian. Ex. H. porosus, Devonian. In general structure Heliopora is similar to Heliolites, but is more branching, whilst Heliolites forms rounded or encrusting masses ; further, the smaller tubes which form the ccenenchyma branch dichotomously in Heliolites, but in Heliopora new tubes are introduced between the older ones. By many writers these two genera are considered to be closely allied, but the relationship is denied by others, who state that important differences are found in the structure of the corallite walls and septa. According to Lind- strom and others, the corallites of Heliolites possess a distinct and v-< ■fvf>- a V'"" - ■-• A QiTY B Fig. 40. Heliolites porosus, Devonian. A. Horizontal section. B. Ver- tical section, a, corallites ; b, tubes forming the ccenenchyma ; c, tabular, x 5. independent wall (theca) and also have true septa, whilst in Heliopora the corallites are simply bounded by the walls of the coenenchymal tubes, and possess pseudosepta instead of septa and these have the form of ridges except at the openings of the corallites. Bourne, on the other hand, considers that the corallites of Heliolites possess no independent wall, and agree in this respect with Heliopora. Although the ccenenchyma of Heliolites resembles closely that of Heliopora, yet Lindstrom and Kiar maintain that it has originated independently in the two genera, and cannot be taken as evidence of relationship ; this view is based on a study of the development and ANTHOZOA 101 phylogeny of Heliolites, and leads to the conclusion that that genus and its allies constitute a specialised offshoot from the early Zoantharia. The great interval of time between the last appearance of Heliolites and first appearance of Heliopora lends some support to the view that these genera are not closely allied ; the former and its allies are not known in rocks of later age than the Devonian, while the latter has been recorded in rocks of Cretaceous and later date only. Poli/tremacis, found in the Cretaceous, is allied to Heliopora. Plasmopora. Allied to Heliolites. Usually discoidal or hemispherical. Walls of smaller tubes incomplete or absent, and their tabulae forming a vesicular tissue. Septa in corallites lamellar, and prolonged outside each calyx, so as to enclose large spaces of uniform size. Basal epitheca with concentric ridges. Ordovician to Devonian. Ex. P. petaliformis, Silurian. Propora. Allied to Plasmopora. Edges of calyces projecting ; septa represented by spines, and not prolonged outside the calyx to enclose large spaces. Ordovician to Silurian. Ex. P. tubulata, Wenlock Limestone. Halysites. Compound ; corallites long and tubular, arranged in a single row and united at their sides so as to form lainina?, which intersect ; in some species the corallites are of two sizes — the smaller perhaps represent the ccenenchynial tubes of Heliolites- Epitheca thick. Septa absent or represented by spines. Tabula? well developed, horizontal or concave. Llandeilo Beds to Wenlock Limestone. Ex H. catenularia, Wenlock Limestone. Chxtetes. Massive, often laminar, consisting of slender, tube-like polygonal corallites ; walls without perforations. Tabula? few, widely separated. Chiefly Carboniferous. Ex. C. radians. The systematic position of Chcetetes is uncertain ; by some authors it has been referred to the Polyzoa. Distribution of the Anthozoa From the point of view of their distribution at the present day, the Madreporaria may be divided into two groups, the solitary and the reef-building. 102 ANTHOZOA The solitary corals (i.e. the corals which do not form reefs) are found in almost all latitudes, but live mainly in rather deep water, the larger number occurring between depths of 50 and 1000 fathoms ; some few (e.g. Garyophyl- lia) live in quite shallow water, whilst others inhabit the depths between 1000 and 2900 fathoms. The species of solitary corals have a wide distribution, being apparently but little affected by conditions of temperature and depth. It might therefore be expected that they would also have a long range in time ; this however is not the case, for existing species extend but a short way back into the geological record, and not a single living form is found fossil in the English Cainozoic formations ; about a third of the living genera, however, are represented in Cainozoic rocks, and a few (e.g. Caryophyllia, Parasmilia, Trocho- cyathus) occur in Mesozoic formations, but none range into the Palaeozoic. The distribution of the reef-building corals, unlike that of the solitary forms, is limited by both depth and tempera- ture. Thus they are found only in shallow water, not usually extending lower than 20 or .30 fathoms, and only where the temperature of the ocean is not less than 65°F.; they flourish only in water warmer than this. Like the solitary corals, the reef-building genera of the present day have but a very limited geological range, only a very few extending back so far as the Mesozoic period. Corals, with possibly one or two exceptions, can only exist in salt water; but Madrepora cribripora is said to inhabit nearly fresh water. Clear water is likewise generally necessary, but one species, Porites limosa, thrives in muddy situations. In geological times, and especially in the Palaeozoic and Mesozoic periods, the reef-building corals had a much wider geographical range than they have ANTHOZOA 103 at the present day, and their remains occur abundantly in various formations in both temperate and polar regions; but in the course of the later Cainozoic period the range of the reef-builders became more and more restricted until the present limits were reached. The Alcyonaria occur in all parts of the world, and are found at all depths from the shore-line down to 2,300 fathoms, but they are most abundant at depths of less than 100 fathoms ; beyond this limit the number of species gradually diminishes as the depth of the water increases. With few exceptions the Zoantharia found in the Pakeozoic formations belong to the Rugose group. The Palaeozoic families which have been referred to the Alcyonaria are almost unrepresented in later formations. Very few of the modern Alcyonarian families occur fossil, but the Pennatulidse are represented in the Trias by Pro- graphularia, in the Cretaceous by Pavonaria, and in the Cainozoic by Graphularia. The red coral, Corallium, is found in the Cretaceous and Cainozoic (perhaps also in the Jurassic) ; forms allied to Gorgonia occur in the Cretaceous and Tertiary rocks ; Isis is found in the Cainozoic, and perhaps also in Cretaceous formations. Spicules, similar to those of Alcyonium, have been detected in the Upper Cretaceous. Heliopora is first recorded from the Cretaceous. The organ-pipe coral, Tuhipora, has not been found fossil. Fossil corals are comparatively rare in argillaceous and arenaceous beds but often abundant in calcareous rocks, many limestones being formed almost entirely of coral remains. This is indeed what might be expected, since existing forms can, as a general rule, live only in clear water. The chief features in the geological distribution of the Anthozoa are given in the following table. 104 ANTHOZOA Cambrian. A few genera which may be corals have been found in the Cambrian in North America, Sardinia and Spain. Ordovician. In North America corals (especially Streptelasma) are common in this system, but in England only a few forms have been found, the most important being Favosites, Heliolites, Haly sites. Silurian. Corals are very abundant, especially in the Wenlock Limestone. Cyathophyllum, Acervularia, Omphyma, Lindstrcemia Goniophyllum, Syringopora, Favosites, Heliolites, Plasmopora, Pro pora, Haly sites. Devonian. Cyathophyllum, Acervularia Phillipsastrwa ( = Smi thia), Cystiphyllum, Calceola, Favosites, Fachypora, Pleurodictyum Heliolites. Carboniferous. Cyathophyllum, Lithostrotion, Clisiophyllum Dibunophyllum, Cyclophyllum, Lonsdaleia, Zaphrentis, Cyathaxonia Caninia, Amplexus, Cleistopora, Michelinia, Syringopora. Permian. Only a very few forms have been found. Trias. Corals are absent in England, but abundant in the Alpine Trias ; most of the Palseozoic forms have become extinct and in place of them are Rhabdophyllia, Cladophyllia, Montlivaltia, Thecosmilia, Isastrcea, Phyllocoenia, Astroccenia, Stylina, Omphalo- phyllia. Jurassic. Montlivaltia, Isastrwa, Thamnastrwa and Thecosmilia are found in the Lias but are not common ; in the Oolites they become very abundant and several other genera also occur, e.g. Stylina, Cyathophora, Cladophyllia, Calamophyllia, Anabacia. Cretaceous. Corals are not abundant in England ; the chief forms are Parasmilia, Trochocyathus, Micrabacia, Holocystis. In some parts of Europe, especially in the Gosau beds (of Chalk age) of the Austrian Alps, corals are very numerous, and include Astroccenia, Montlivaltia, Isastrwa, Cyclolites, Thamnastrwa, etc. Cainozoic. Corals are rare in English Cainozoic formations : Turbinolia, Dendropkyllia, Ocidina and Goniopora (Litharwa) occur in the Eocene ; Madrepora in the Oligocene ; Flabellum in the Pliocene. In the middle and south of Europe, corals are found abundantly in various Cainozoic deposits. PHYLUM ECHINODEKMA Sub-Phyla 1. Eleutherozoa 2. Pelmatozoa Classes 1. Asteroidea. 2. Ophiuroidea. 3. Echinoidea. 4. Holothuroidea. 1. Crinoida. 2. Cystidea. 3. Blastoidea. 4. Edrioasteroidea The animals included in this division are all marine ; they comprise the star-fishes, brittle-stars, sea-urchins, sea-lilies, sea-cucumbers, and the extinct blastoids and cystideans. The body is very often radially symmetrical, the symmetry being generally pentamerous. But in many cases there is also a more or less well-marked bilateral arrangement of parts. The echinoderms are never compound animals. In the majority of cases the alimentary canal terminates in an anus. A body-cavity or coelom is present and surrounds the alimentary canal. The water- vascular system (fig. 43) is one of the distinguishing features of the group : it con- sists of a set of vessels containing a watery fluid and generally placed in communication with the sea-water by means of a canal ; one vessel forms a ring round the oesophagus from which radiating trunks are given off. The water-vascular system functions in respiration and as a sensory organ, and generally also in locomotion. A nervous system is present ; one part of it has a distribution 106 ECHINODERMA similar to that of the water-vascular system. Repro- duction is mainly sexual ; as a rule the sexes are separate, but do not differ externally. In nearly all echinoderms there is a dermal skeleton. This is calcareous and consists sometimes of isolated pieces, but more usually of rods or plates united by fibres of con- nective tissue and forming a complete shell or test, which may be either flexible or rigid ; spines and other processes are often attached to the plates. When examined micro- scopically each part of the skeleton is found to be formed of a network of calcareous rods (fig. 41). The details of the structure vary in different forms, depending on the m <5§ m£m*«&?n < At mm (• :£m mb. e ■JoSm **WH $J &j £^ la B Fig. 41. A. Portion of transverse section of a spine of a sea-urchin, Echinometra, Eecent. Magnified. B. Section of interambulacral plate of recent Cidaris cut parallel to the surface. Magnified. size and shape of the spaces between the rods. In the spines of sea-urchins the network of rods has usually a radial arrangement, with polygonal or rectangular spaces (fig. 41 A), except at the centre, where the structure is more irregular. Another characteristic feature of the skeleton is that each component part shows the optical characters of a crystal of calcite, and differs only from an ordinary crystal in not having crystal contours and in the ECHIXODERMA 107 possession of the netted structure. In a plate the princi- pal crystallographic axis is at right angles to the surface, in a spine it is parallel with the length. In fossil specimens the spaces in the network of rods usually become filled with calcite, which is deposited in crystalline continuity with that forming the plate or spine. In such cases the characteristic cleavage of calcite becomes well marked, so that when the plate or spine is broken, the fracture passes along the cleavage planes, instead of being irregular as in the recent forms. By the infiltration of calcite and the development of cleavage, the organic structure in fossil echinoderms is sometimes partly or almost completely destroyed. The Echinoderma are divided into two main groups, (1) the Eleutherozoa, (2) the Pelmatozoa. I. ELEUTHEROZOA The Eleutherozoa possess no fixing organ and are able to move about freely. This group is divided into four classes: — (1) Asteroidea, (2) Ophiuroidea, (3) Echinoidea, (4) Holothuroidea. CLASS I. ASTEROIDEA The Asteroidea or star-fishes have a flexible body which may be pentagonal in outline, but is usually more or less star-shaped, consisting of a central part, known as the disc, and of five broad arms or rays. In a few forms there are more than five arms, e.g. Solaster papposus has thirteen. The mouth is at the centre of the disc on the under surface, and along the under surface of each arm are rows 108 ECHINODERMA. ASTEROIDEA of tubular processes, the tube-feet, which are connected with the radial water- vessel. This surface of the body is called the oral, ambulacral, actinal, or ventral surface. The upper surface is aboral, anti-ambulacral, abactinal, or dorsal ; on it usually occur the anus and madreporic plate. The anus is situated near the centre of the disc, but in some forms {Astropecten) is absent. The madreporite or madreporic plate is a porous plate placed between two of the rays on the disc ; sometimes more than one is present. On the oral surface, extending from the mouth to the tip of each arm, is a deep groove, the ambulacral groove ; this is formed by two rows of plates known as the ambulacral ossicles (fig. 42, a), f a a f which meet at an angle ; the ossicles on one side of the groove are movably articulated with those opposite. Along each side of the ambulacral ^. Eig. 42. Section of the arm groove there IS a row of pores, of a star-fish (Astropecten). each pore being between two «Ltm1bulac1ra! °fssicles ;- h ad_ r & ambulacral plates ; c, mfero- OSsicles ; generally the pores marginal plates with spines ; ■i • , • I , v d, supero-marginals ; e, radial are arranged in a straight line, wate£ vessel .^ ampu'lla . g% but in some forms they are tube-feet. Enlarged, zigzag, being alternately near to, and distant from, the middle of the ambulacral groove. External to the rows of ambulacral ossicles there is, on each side of the groove, another row of plates, the ad-ambulacral plates (b). At the sides of the arms there are in many cases two rows of marginal plates (c, d) — the super o- and infer o-marginals. In some forms marginal plates are small or absent. The aboral surface of the skeleton is often formed of a mesh- work of calcareous rods with leathery skin in the inter- spaces, but in some forms rows of distinct plates extend ECHINODERMA. ASTEROTDEA 109 along the arms, and on the aboral surface of the disc there is sometimes a central plate with others arranged in circles around it. Short spines are often abundant. Pedicellarice are also of frequent occurrence, especially on the aboral surface ; they are modified spines consisting typically of two movable blades which are often borne on a stalk, and serve to remove foreign bodies from the surface of the animal. Projecting into the mouth at the angles formed by the ambulacral grooves are five pairs of plates, which give the mouth a star-shaped form. The mouth leads into a short oesophagus which opens into the globular stomach ; above the stomach is the pentagonal pyloric sac, from the angles of which are given off branches, which soon divide into two, and ex- tend down the arms near the aboral surface. From the pyloric sac a short narrow intestine leads to the anus at the centre of the aboral surface. The water- vascular system consists of a vessel forming a ring round the oesophagus (fig. 43, a), from which ring a branch (6) is given off to each arm and is placed in the ambulacral groove outside the skeleton. Each of these radial vessels Fig- 43- Diagram of the water _ vascular system of a star-fish gives Oft two TOWS Ot processes a, circular vessel round the on opposite sides, which pass through the pores between the ambulacral ossicles into vesicles situated above the ossicles and known as the mouth ; b, radial vessels ; c, Polian vesicles ; d, stone-canal ; e, madreporic plate ; /, tube-feet (only a few shown) ; g, ampulla. 110 ECHINODERMA. ASTEROIDEA ampullce (g), and also into the tubular processes known as the tube-feet (f), which project along the under surface of the arm and are provided at their extremities with sucking- discs. The discs become attached to foreign bodies, and by means of the contraction of the tube-feet the animal moves. The water- vascular system is placed in com- munication with the exterior by a canal (fig. 43, d) passing from the circular vessel to the aboral surface of the disc and ending in the madreporic plate. This is known as the stone-canal on account of the deposit of carbonate of lime in its walls. On the aboral surface, and sometimes upon other parts of the body also, there are tube-like projections of the skin, which form simple respiratory organs known as dermal branchice. The distribution of the main part of the nervous system is similar to that of the water-vascular system. It consists of a ring round the mouth and of a branch which extends down the ambulacral groove of each arm ; there is also a layer of fine nerve-fibres under the ectoderm. At the tip of each arm is an eye-spot. The genital glands occur in pairs at the base of each arm and open to the exterior between the rays ; generally the openings are on the aboral surface, but in a few cases on the oral surface. Palaeaster. Body pentagonal. Disc small. Arms thick, convex, of moderate length ; upper surface formed of rows of small ossicles provided with spines. Ambulacral ossicles alternating on either side of the deep ambulacral groove. There is a row of ad-ambulacral plates and a row of large marginal plates. Madre- poric plate small. Bala Beds to Carboniferous. Ex. P. euckaris, Devonian. Palaeasterina. Disc large, pentagonal. Arms short, but distinctly marked off from the disc ; ambulacral ossicles alternating ; marginal plates smaller than ad-ambulacrals and usually with small ECHINODERMA. ASTEROIDEA 111 spines. Ad-ambulacrals boot-shaped. Disc with rounded isolated plates ; on the aboral surface a central plate is surrounded by a circle of five pairs of plates, and four rows of plates occur on the aboral surface of each arm. Ordovician and Silurian. Ex. P. primceva, Ludlow. Calliderma. Body flattened, pentagonal-stellate, with the rays moderately long. Marginal plates large, forming a broad border to the disc, covered with granules. Aboral surface of disc with small plates arranged regularly. Cretaceous to present day. Ex. C. smithice, Chalk. Metopaster. Body flattened, pentagonal in outline, the rays only slightly produced. Marginal plates thick, covered with punc- tations and surrounded with a depressed border. Supero-marginal plates few in number, forming a broad border to the disc ; the terminal pair of plates the largest. Aboral surface covered with small polygonal (usually hexagonal) plates. Infero-marginal plates more numerous than the supero-marginals. Plates on the oral surface small, polygonal. Cretaceous. Ex. M. parkinsoni, Upper Chalk. Mitraster. Similar to Metopaster, but rounded (or slightly pentagonal) in form, with supero- marginal plates few and all of equal size. Chalk. Ex. 31. hunteri. PalaBOCOma. Arms rather short. Ambulacral grooves narrow and shallow ; ambulacral ossicles numerous and alternating on either side. Ad-ambulacral plates large ; the adjoining row of plates with numerous long spines. Disc with very small plates. Silurian. Ex. P. marstoni, Ludlow. Distribution of the Aster oidea The Asteroidea have a wide distribution in the ocean at the present day ; they are most abundant at moderate depths, but also occur in abyssal regions. The fossil forms do not differ greatly from the modern ones, but many of those found in the Paleozoic formations 112 ECHINODERMA. ASTEROIDEA have the ambulacral ossicles alternating on either side of the ambulacral groove. The earliest star-fishes are found in the Tremadoc Beds (Upper Cambrian). The genus Palceaster appears in the Bala Beds. The group is more abundant in the Silurian, where Palceaster, Palwasterina, U raster ellay Lepidaster, and Palceocoma occur. P alabaster, Aspidosoma and many others are found in the Devonian. Jurassic forms have been referred to the genera Solaster, Astrospecten, and Plumaster. Calliderma, Metopaster, Pentagonaster, and Mitraster occur in the Upper Cre- taceous. In the Cainozoic rocks of England star-fishes are rare. CLASS II. OPHIUROIDEA In the Ophiuroids or brittle-stars, the body consists of a disc and arms. The arms are generally five in number, usually simple, but in some cases branched ; they are much smaller than in the star-fishes and are sharply marked off from the disc and do not contain prolongations of the generative and digestive systems. Usually they are long, cylindrical, and very flexible, serving for locomo- tion by means of movements which take place chiefly in a horizontal direction ; the ambulacral groove is not open to the exterior except, apparently, in a few Palaeozoic forms. The arrangement of the nervous and the water-vascular systems is similar to that found in the Asteroidea, but the tube-feet are not provided with sucking-discs and there are no ampullae. The madreporic plate is on the oral surface. There is no anus, and pedicellariae are nearly always absent. Generally there is a well-developed skeleton. In a ECHINODERMA. OPHIUROIDEA 113 typical case the followiug parts are found : — Encasing the arms there are four rows of plates (fig. 44), one dorsal, one ventral, and two lateral. The lateral plates are provided with rows of spines. Between the lateral and the ventral plates are apertures for the passage of the tube-feet. The greater part of the space en- closed by the four rows of plates is filled up by a longi- b tudinal row of ossicles (d) ; J = each ossicle consists of two parts which are nearly always Fifn %hiS°^»» t fused together along the dorsal plate ; b, lateral plate ; I- -• i t t-< i c? ventral plate; d, ambulacra! median vertical line. Each ossicles fused along the median Ossicle in the row articulates vertical line ; e, ambulacral groove. Enlarged, with the preceding and suc- ceeding one, so that the arm is flexible. On the uncler- surface of the row there is a groove (e) in which the water- vascular vessel and the nerve cord are placed; this corresponds to the ambulacral groove of the star-fish, and the plates above represent the ambulacral ossicles. The disc is usually round or pentagonal. On its oral surface (fig. 45 A) the arms are prolonged so as to reach the mouth. The last pair of ambulacral ossicles, — those next the mouth, instead of being fused like the others, remain free, and each ossicle unites with that of the adjoining arm. The parts of the disc between the arms are known as the interbrachial areas ; these are covered mainly with scaly plates and granules, but in each of the areas there is one large plate, the buccal plate (b), and other smaller plates, projecting into the mouth, giving it a stellate form. One of the buccal plates serves as the madreporic plate. The genital openings (g) also occur on W. r. 8 114 ECHINODERMA. OPHIUROIDEA the oral surface of the disc ; they are in the form of slits in the interbrachial areas, usually two in each, situated near the bases of the arms ; occasionally there are four. The aboral surface of the disc (fig. 45 B) is, in most cases, covered with numerous small plates ; but usually there is Fig. 45. A. Ophiura, Recent. Oral surface of disc and part of the arms, b, buccal plates ; a, genital slits ; v, ventral plates of arms. B. Ophioglypha, Recent. Aboral surface, r, radial plates ; I, lateral plates of arms ; d, dorsal plates of arms. xli. at the bases of the arms on each side a large plate, the radial plate (r) ; there may also be a large plate at the centre of the disc surrounded by one or more circles of five plates. On this surface the arms end abruptly at the margin of the disc. Protaster. Disc well marked, with fairly large scales. Arms five, long, tapering, without ventral plates ; ambulacral ossicles boot-shaped, alternating, not united. Ordovician and Silurian. Ex. P. sedgivicki, Silurian. Lapworthura. Disc circular, well marked. Arms flexible, broad, at first of uniform width, afterwards tapering ; ambulacral ossicles opposite, fused, their distal and proximal margins parallel, with plain articular surfaces ; ventral arm-plates and buccal plates absent. Madreporic plate dorsal, large. Ludlow Beds. Ex. L. miltoni. ECHINODERMA. OPHIUROIDEA 115 Distribution of the Ophiuroidea At the present day the majority of the Ophiuroids live in shallow water, more than half of the known species being found at a depth of less than 30 fathoms, and most of these not extending lower. Other forms occur at greater depths, as many as 69 species being found below 1000 fathoms. Ophiuroids are rare as fossils; the earliest known form occurs in the Bala Beds, and belongs to the genus Protaster; this genus ranges on to the Silurian, where Laptvorthura, Eucladia and others appear. In the De- vonian, Furcaster and several other genera are found ; in the Trias, Aspidura. In the Jurassic Geocoma, and forms which have been referred to the existing genera Ophiura, Ophiolepis and Ophiocten are present. In the Cretaceous Ophiura and Amphiura are found. A few, such as Ophioglypha, occur in the Eocene. CLASS III. ECHINOIDEA The echinoids or sea-urchins have usually a globular, heart-shaped, or discoidal body, covered with spines. The shell or test is covered by a layer of ectoderm and consists of numerous calcareous plates, which, in the majority of cases, are immovably united. Nothing corresponding to the ambulacral groove of the star-fish is to be seen on the surface, since the water-vascular system is internal to the skeleton, and as a result the tube-feet, in order to reach the exterior, must pierce the plates of the test. With one exception the mouth is always on the inferior surface ; it is either central or placed in front of the centre. The anus is either at the summit of the test or posterior to it, somewhere along 8—2 116 ECHINODERMA. ECHINOIDEA a line drawn from the summit to the centre of the base. In the regular echinoids both anus and mouth are central — being placed at opposite poles of the test ; in the irregular echinoids the anus is always, and the mouth often, excentric. In the test we may distinguish three parts : a small patch of plates placed at the summit, known as the apical disc or apical system ; a series of plates surrounding the mouth ; and the remainder of the test termed the corona. o— ,-m --o g- Fig. 46. A. Diagram of the upper surface of a regular echinoid, with the tubercles and spines omitted, a, ambulacral areas ; b, inter- ambulacral areas ; p, pores in the ambulacral plates. B. Apical disc of Echinus esculentus, Recent, a, anus ; p, peri- proctal membrane with small plates ; g, genital plates, each with a pore ; m, madreporic plate ; o, ocular plates, x 1-^. In a typical echinoid of the regular group (e.g. Echinus) the anus is placed within the apical disc (fig. 46 B), which then consists of the following parts. Near the centre is the anus (a), which is surrounded by a membrane covered with scaly plates and known as the periproct (p). The ECHINODERMA. ECHINOIDEA 117 periproct is encircled by a ring formed of ten plates, five are called genital (g) and five ocular (o). The genital plates form the inner part of the ring ; they are often more or less hexagonal in outline, and are usually provided with a perforation which serves as the opening for the genital ducts — whence their name ; one is pierced by numerous pores and is the madreporic plate (m). Outside the genital plates and alternating with them are the ocular plates ; these are smaller than the genital and usually triangular or pentagonal, and each has a perforation through which ■— m s.— m Fig. 47. Some types of apical disc. A. Peltastes wrighti, Lower Greensand. B. Echinocorys vulgaris, Upper Chalk. C. Collyrites bicordata, Corallian. D. Palceechinus, Carboniferous Limestone. E. Galerites subrotundus, Chalk. In the figures the ocular plates are distinguished by dots, the genital plates by lines, m, madreporic plate; a, anus; b, sur-anal plate. All enlarged. the termination of the radial water- vessel projects, bearing at its tip a rudimentary visual organ1. 1 The genital plates are sometimes termed basals and the oculars are also known as radials, since, by some authors, they have been considered to represent the plates which bear those names in other groups of the Echinoderma. It is more probable that, although occupying similar positions, they have originated independently in the different groups. 118 ECHINODERMA. ECHINOIDEA In most of the regular echinoids the apical disc is large, but particularly so in Gidaris, Salenia, Peltastes, and their allies. In a few regular forms (fig. 47 D) the genital plates are completely separated from one another by the oculars, so that a single row of ten plates encircles the periproct. Each genital plate has usually one perforation only, but in many Palaeozoic forms (fig. 47 D) there are three or more, and in Gidaris often two. Similarly the oculars in some Palaeozoic echinoids have two perforations instead of one. In Salenia and Peltastes there is an extra plate in the apical^disc ; it is in front of the periproct and is known as the sur-anal plate (fig. 47 A, b). In the irregular echinoids the apical disc is small, since it does not enclose the periproct. The madreporic plate extends to the centre of the disc (fig. 47 E, m), and some- times (Spatangas) reaches to the posterior border, separating the posterior oculars. The posterior genital is sometimes absent (fig. 47 B), and when present may be without a perforation (fig. 47 E). In Echinocorys and Holaster the apical disc is elongated, and the anterior genitals are separated from the posterior genitals by two oculars which join in the middle (fig. 47 B) ; in Gollyrites (C) the apical disc is still more elongated, since the two posterior oculars are separated from the rest of the apical disc by a chain of small plates. The corona consists of twenty columns of plates, each column extending from the apical disc to near the mouth. The plates are of two kinds, ambulacral (fig. 46 A, a) and inter ambidacral (b) ; they are arranged in pairs, there being five double columns of ambulacrals separated by five double columns of interambulacrals ; each double column is termed an area. The former end against the ocular plates, the latter against the genital, and in each case ECHINODERMA. ECHINOIDEA 119 fresh plates are developed next the apical disc. In each area the plates alternate on either side, and since their inner ends are angular, the line between the two rows is zig-zag. The ambulacral plates are smaller and more numerous than the interambulacral, and they are perforated by pores (p) for the passage of the tube-feet to the exterior, a radial water-vessel being placed under each ambulacral area. The pores may be round or elongated ; they are situated in the outer portion of the plates and are almost always in pairs ; each pair of pores corresponds to a single tube-foot, since each tube-foot divides at its base into two canals. Frequently each pair of pores is surrounded by an oval raised rim (fig. 48). In some echinoids, such as Cidaris, each ambulacral plate is formed of one piece only (as in fig. 46) — such plates are called simple primaries. Id other cases some of the ambulacral plates are compound, consisting of several small plates which have become fused together ; but the original plates are still indicated by the lines of suture between them and also by the pair of pores on each (fig. 48) ; in some echinoids (fig. 48 A) the plates which are united are all pri- maries— that is to say, each extends from the margin to the middle line of the ambula- cral area ; but frequently some Fig# 48> compound Ambulacral of the plates taper away and Plates- A- Pseudodiadema 1 A hemi splicer i cum, from the Co- do not reach the middle line rallian, formed of three fused for innpr edcre of tho pom- plates. B.Phymosomakoenigi, ^or inner eage oi me com from the chalk< formed of six pound plate) — Such are Called fused plates. Enlarged. clemi-plates {e.g. the middle plates in fig. 48 B). This fusion of plates is usually stated to be due to growth- pressure — since each plate of the test is enlarging and 120 ECHINODERMA. ECHINOIDEA new plates are being added next the apical disc ; the fact that some of the fused primary plates are smaller than others, and also the presence of demi-plates, is attributed to the reduction in size of the original plates by the absorption of material under pressure. Lambert, however, considers that the difference in size of plates is due mainly to the more rapid superficial growth of the plates on which large tubercles are developed. The pores in the ambulacra of some echinoids are placed one immediately above the other, so that one vertical row of pore-pairs is seen — such pores are termed unigeminal (fig. 46) ; in other cases the pore-pairs are alternately near to, and more distant from, the margin of the ambulacral plate, and consequently two vertical rows are formed, and the pores are said to be bigeminal ; in a similar way three vertical rows of pore- pairs may be produced, when the pores are known as trigeminal. Sometimes the pores in each pair are united by a groove on the surface of the plate, and are then termed conjugate. In some sea-urchins the two rows of pores in each ambulacral area diverge rapidly after leaving the apical disc, and then come together again before reaching the equator, so that this part of the ambulacrum is leaf-like, and the five ambulacra together form a rosette on the upper surface of the corona, the pores being but irregularly developed on the lower surface; the ambulacral areas in such cases are termed petaloid (e.g. Scutella), but when the rows of pores diverge but do not come in contact at their lower ends they are sub-petaloid (e.g. Nucleolites). When, as in Cidaris, the distance be- tween the two rows of pores increases uniformly and slowly in passing from the apical disc to the equator, and the pores are equally well-developed on the under surface of the test, the ambulacra are said to be simple (fig. 46). ECHINODERMA. ECHINOIDEA 121 With only a few exceptions the corona in the Mesozoic and later echinoids is formed of twenty columns of plates, as described above ; but in the Palaeozoic echinoids, more than twenty columns of plates are found (fig. 51), except in the earliest-known genus Bothriocidaris (Ordovician), which is remarkable in having only one column of plates in each interambulacral area, with the usual two columns in each ambulacral area. In other Palaeozoic forms the number of columns is variable and often great, so that the total number of plates in the corona becomes considerable : thus, Archceocidaris possesses two columns in each am- bulacrum, and from four to seven in each interambulacrum ; Oligoporus has four ambulacral and from four to nine interambulacral rows ; Melonechinus, five to fourteen am- bulacral, and from four to eleven interambulacral columns ; whilst Lepidesthes consists of from eight to as many as eighteen ambulacral, and three to six interambulacral columns. In these Palaeozoic forms each ambulacral plate possesses one pair of pores. In most echinoids the test is rigid, but in some the plates of the corona overlap to a slight extent, giving some flexibility to the test ; such is the case in several Palaeozoic genera, and also in a few later forms, viz. Pelanechinus from the Corallian, Echinothuria from the Chalk, and some living species of the deep-sea Asthenosoma and Phormo- soma. The plates of both the ambulacral and interambulacral areas are often provided with rounded elevations known as tubercles and granules. The tubercles are of various sizes, the largest being the primary. In these the follow- ing parts may be distinguished : at the summit a hemi- spheroidal piece, sometimes perforated at the top, and known as the mamelon (fig. 49 B, m). The mamelon rests 122 ECHINODERMA. ECHINOIDEA -b —a • c ■h Fig. 49. on the boss (b), the upper margin of which is sometimes smooth, sometimes crenulated. The base of the boss is frequently surrounded by a smooth excavated space, the areola or scrobicule (a), to which muscles from the spine are attached. The granules are smaller than the tubercles and have no distinct mame- lon. Attached to the tubercles are the spines or radioles ; these are of different sizes and shapes in different genera and species and even on the same individual,being needle- like, rod-like, or flask-shaped; the larger spines are attached to the primary tubercles, the smaller to the secondary tubercles. They serve for protection and also assist in locomotion. At the end of the spine, where it articulates with the mamelon, there is a rounded cavity, the acetabulum (fig. 49 A, a) ; next comes the head (h) limited above by a ring or collar (c), which may be smooth or crenulated and serves for the attachment of the muscles that move the spine. Beyond the collar and forming the greater part of the spine is the shaft or stem (b), which may be smooth, or ornamented with ridges or rows of spiny processes. The microscopic structure of the spines (fig. 41 A) varies in different genera, and is of some importance in classification. Pedicellarise, which consist of a stalk with usually three blades, also occur, but are rarely found fossil. A. Spine of Cidaris Jiorigemma, from the Corallian Rocks, a, acetabulum ; h, head or base ; c, collar ; b, shaft or stem. B. Ambulacral plate of Cidaris (recent) with a large primary tubercle and secondary tubercles. In the primary tubercle, in, mamelon ; b, boss ; a, areola. Natural size. ECHINODERMA. ECHINOIDEA 123 3^ On the surface of some irregular sea-urchins belonging to the sub-order Atelostomata (p. 129) there are bands which appear to be nearly smooth, but are covered with very minute tubercles; in the living state they bear slender modified spines. These bands are termed fascioles, and their position varies in different a genera ; sometimes they form a ring beneath the anus (e.g. Micraster, fig. 50, c), when they are said to be sub-anal; in other cases they encircle the rosette formed by the petaloid ambulacra (e.g. Hemiaster) and are said to be peripe- talous ; or they extend round the margin of the test (e.g. Epiaster). On the lower surface there is an opening in the corona known as the peristome (fig. 50, a) ; this is closed by a membrane in the centre of which is the mouth. The peristomal membrane is sometimes (e.g. Cidaris) completely covered with rows of scaly plates, but more usually bears small isolated plates only. The peristomal membrane and its plates are usually lost in fossil specimens. The shape of the peristome varies in different genera, it may be circular, oval, pentagonal, or decagonal ; at its margin there are frequently ten notches, by which the five pairs of gills or branchiae pass to the exterior. The peristome is usually larger in the regular than in the irregular echinoids. In some irregular echinoids belonging to the sub-order Atelostomata (p. 129) the parts of the Fig. 50. Under surface of Micra- ster cor-anguinum from the Upper Chalk, showing fasciole. a, peristome ; &, periproct ; c, fasciole. x f . 124 ECHINODERMA. ECHINOIDEA ambulacra near the peristome are depressed and leaf-like, whilst the intervening interambulacra are convex ; this part of the corona has consequently a petaloid appearance, and is known as the floscelle. At the commencement of the alimentary canal there is, in some genera, a complicated calcareous apparatus which functions in mastication ; this is composed chiefly of five jaws, which are moved by means of muscles attached to ridges at the margin of the peristome — these ridges constitute what is known as the perignathic girdle. This may consist of ridges arising from the interambulacral plates only, or there may be also processes from the sides of the ambulacral plates, and these often unite, forming an arch or auricle over each ambulacral area at the margin of the peristome. The first part of the alimentary canal passes through the centre of the masticatory apparatus. The circular vessel of the water-vascular system forms a ring round the oesophagus at the top of the masticatory apparatus; this ring gives off five radial branches which pass through the auricles and up the inside of each ambulacral area. In the irregular echinoids there is a well-marked bilateral symmetry ; a plane which passes through the anus (which is in the posterior interambulacral area), the apical disc, and the mouth, divides the body into two similar parts. The ambulacra in these forms often differ considerably in size, and, to some extent in structure ; the anterior one may be smaller than the others and frequently has a different arrangement of pores, while the four other ambulacra are paired. The interambulacra are also un- like— the posterior one often forming a large part of the base of the test. The bilateral character is not conspicuous ECHINODERMA. ECHINOIDEA 125 in the regular sea-urchins, but the plane of symmetry may be found by means of the madreporic plate, which is always placed at the upper end of the right anterior interambulacral area. The Echinoidea may be divided into two Orders, (1) Regularia, (2) Irregularia. ORDER I. REGULARIA The mouth is at the centre of the base, and the anus within the apical disc. The ambulacra are simple. Jaws are present in all. The test is circular in outline. Palaeechinus (fig. 47 D). Test spheroidal, rigid. Apical disc with five large genital plates, each with three perforations, — but in some cases one of the genitals may have a single perforation. Ocular plates five, small, each with two perforations. Ambulacra narrow, straight, with two rows of j^lates, and smaller plates at the margins ; two vertical rows of pairs of pores on each side of the area. Interambulacra wide, with five to seven rows of plates at the equator, fewer towards the poles; plates hexagonal, except those next the ambulacral area, which are pentagonal ; surface of plates covered with granules. Spines small. Upper Silurian to Carboniferous Limestone. Ex. P. intermedins, Carboniferous. Melonechinus ( = Melonites) (fig. 51). Test large, elliptical, with furrows from apex to peristome. Apical disc with five genital plates, each having from two to five pores. Ambulacra broad, concave on each side of a median ridge, with five to fourteen columns of plates, each plate with a pair of pores ; four plates at the peri- stomal edge of each area. Interambulacra consisting of four to eleven columns of small thick plates, which are pentagonal next the ambulacra, hexagonal elsewhere ; tubercles very small. Jaws large. Carboniferous. Ex. M. multiporus. Archaeocidaris ( = Echinocrinus). Test large, plates over- lapping. Ambulacra narrow, formed of two rows of plates ; pores unigeminal. Interambulacra consist of from four to seven rows of large plates, the middle ones being hexagonal ; each plate has 126 ECHINODERMA. ECHINOIDEA a large primary perforated tubercle which bears a long spine. Peristomal membrane covered with plates. Carboniferous Lime- stone. Ex. A. urii. Fig. 51. Melonechinusmultiporus, Carboniferous. Part of an ambulacral area (a) and an interambulacral area (b) from the equator of the test. Based on figures given by Jackson, x 2. Cidaris. Test spheroidal, the summit and base equally flat- tened. Apical disc very large, rarely preserved fossil, ocular plates large. Ambulacra narrow, flexuous, plates simple, pores unigeminal ; between the rows of pores are vertical rows of small tubercles and granules. Interambulacra wide, plates large, each with a primary tubercle which is perforated, and may be crenulated or smooth ; areola large, surrounded by secondary tubercles, beyond which may be granules. Peristome rounded, its membrane covered with plates. Spines large, of various forms, generally ornamented with rows of granules. The term Cidaris is here used in the extended sense, and really includes several genera. Jurassic to present day ; allied forms occur in the Trias. Ex. C. florigemma, Corallian and Kimeridgian. Peltastes (fig. 47 A). Test circular in outline, depressed. Apical disc very large, prominent, containing one extra plate, the sur-anal, placed in front of the periproct ; the madreporic plate has an oblique fissure. Ambulacra narrow, straight or slightly flexuous, with small tubercles ; pores unigeminal except near the peristome ; ambulacral plates, simple primaries. Interambulacra wide, with large primary tubercles, which are imperforate, but may be crenulate. Peristome slightly notched. Upper Jurassic to Gault. Ex. P. wrighti, Lower Cretaceous. Salenia. Similar to Peltastes, but the periproct is placed to the right of a median line drawn from the anterior to the posterior ECHIXODERMA. ECHINOIDEA 127 margin. Cretaceous to present day. Ex. 8. petalifera, Upper Greensand. Acrosalenia. Form similar to Peltastes. Apical disc rather large ; genital plates large, the posterior smaller than the others and differing in shape. One or more sur-anal plates in front of the periproct, which is in the antero-posterior line. Pores unigeminal except near the peristome. Interambulacra with large perforate tubercles. Spines smooth or striated. Lias to Cretaceous. Ex. A. spinosa, Inferior Oolite to Corallian. Hemicidaris. Test spheroidal, inferior surface flattened. Apical disc small. Ambulacra narrow on the upper surface, slightly flexuous, with two rows of tubercles below the equator, which pass into granules on the upper surface ; plates below the equator com- pound, each formed of three fused plates. Pores unigeminal, but bigeminal near the peristome. Interambulacra broad ; plates large and few, each with a large perforate and crenulate tubercle, and also smaller tubercles and granules. Spines cylindrical, long. Peristome large, decagonal. Inferior Oolite to Cretaceous. Ex. H. intermedia, Corallian. Pseudodiadema (fig. 48 A). Test circular or slightly poly- gonal, depressed. Apical disc and periproct large. Ambulacra straight, narrower than the interambulacra, with two rows of crenu- late and perforate tubercles ; plates compound, each consisting of three fused primaries, the middle being largest, usually with three pairs of pores on each plate, unigeminal. Interambulacra with two or more rows of primary crenulate and perforate tubercles. Peri- stome large, decagonal. Lias to Tertiary. Ex. P. ornatum, Lower Chalk. Hemipedina. Test circular or slightly polygonal, depressed. Apical disc rather large. Ambulacra narrow, plates formed of three fused primaries (but simple near the apical disc), pores unigeminal ; two rows of tubercles, perforate, not crenulate. Interambulacra with two (sometimes more) vertical rows of primary, perforate, not crenulate tubercles. Spines of moderate length, finely striated. Peristome with slight incisions. Lias to present day. Ex. H. ethe- ridgei, Lias. 128 ECHINODERMA. ECHINOIDEA Diplopodia. Form and tubercles similar to Pseudodiadema. Pores bigeminal near the apex and peristome, unigeminal at the equator. Plates at the equator composed of four primary plates or sometimes the lowest plate is a demi-plate. Jurassic and Cretaceous. Ex. D. versipora, Corallian. Stomechinus. Test hemispherical. Genital plates rela- tively large, projecting outwards ; oculars small. Ambulacra wide, plates formed of three primaries — the middle one largest ; pores trigeminal. On each ambulacral and interambulacral area are two vertical rows of primary, imperforate, non-crenulate tubercles, of about the same size on each area ; also secondary tubercles and granules, usually numerous. Peristome large, with ten deep in- cisions. Inferior Oolite to Lower Cretaceous. Ex. S. bigranularis, Inferior Oolite. Pbymosoma ( = Cyphosoma) (fig. 48 B). Form similar to Pseudodiadema. Ambulacral plates high, compound, each may consist of four, five, or six fused plates (some being demi-plates) with the same number of pairs of pores ; two rows of primary imper- forate tubercles ; pores unigeminal except near the apical disc. Interambulacra with two or more rows of primary imperforate tubercles. Jurassic to Eocene ; common in the Chalk. Ex. C. koeyiigi, Upper Chalk. Echinus. Test more or less hemispherical. Apical disc as in fig. 46 B. Ambulacra rather narrow, trigeminal, plates consisting of a lower primary, a middle demi-plate, and an upper primary or demi-plate. Two vertical rows of small, primary tubercles on each area, and often numerous secondary tubercles. Peristome rather small, circular, with small incisions. Cretaceous to present day. Ex. E. ivoodivardi, Pliocene ; E. escidentus, Pliocene and living. ORDER II. IRREGULARIA The anus is placed outside the apical disc, in the posterior interambulacral area. The raouth is either central or in front of the centre. The test is bilaterally ECHINODERMA. ECHINOIDEA 129 symmetrical. Ambulacra simple or petaloid. Jaws may be present or absent. SUB-ORDER 1. GNATHOSTOMATA Mouth central. Jaws and perignathic girdle present. Galerites ( = Echinoco?ms, Gonulus) (fig. 47 E). Test conical, or almost hemispherical, inferior surface flat, outline pentagonal or oval. Apical disc small. Ambulacra narrow, straight, simple ; pores unigeminal, but trigeminal near the mouth. Interambulacra with broad plates, tubercles very small, perforated and crenulated. Peristome small, central, decagonal. Periproct marginal or sub- marginal. Upper Greensand to Upper Chalk. Ex. G. conicus, Upper Chalk. Hole cty pus. Test hemispherical, depressed, base excavated. Apical disc small. Ambulacra narrow, straight, simple ; pores uni- geminal, tubercles small. Interambulacra formed of rather large plates, with small tubercles. Peristome central, decagonal. Peri- proct large, placed between the peristome and the posterior margin of the test. Upper Lias to Corallian ; also foreign Cretaceous. Ex. H. kemisphericus, Inferior Oolite. Discoidea. Form similar to Holectypus. On the base of the interior are ten vertical plates extending from the margin of the test towards the mouth, and placed one on each side of the ambulacral areas. Cretaceous. Ex. D. cylindrical Chalk. Pygaster. Test large, depressed, outline pentagonal or circular, base concave. Apical disc small ; madreporic plate large, extending to the front of the periproct. Ambulacra straight, simple ; pores unigeminal ; tubercles in vertical rows. Interam- bulacra wide, tubercles perforate. Peristome central, large, decagonal. Periproct very large, placed just behind the apical disc. Inferior Oolite to Cretaceous. Ex. P. umbrella, Corallian. SUB-ORDER 2. ATELOSTOMATA No jaws or perignathic girdle. The bilateral symmetry of the test is particularly well-marked. Hyboclypeus. Test oval, depressed, anterior part usually w. p. 9 130 ECHINODERMA. ECHINOIDEA more elevated. Apical disc elongated — the two anterior genitals separated from the two posterior by two oculars. Ambulacra simple, pores unigeminal. Interambulacra wide. Tubercles very small. Periproct next the apical disc, in a long groove on the dorsal surface. Peristome a little in front of the centre. Inferior Oolite to Coral- lian. Ex. H. gibbemhcs, Inferior Oolite. Nucleolites ( = Echinobrissus). Test depressed ; outline oval or quadrilateral, rounded anteriorly, truncated and broadest poste- riorly ; inferior surface concave. Apical disc compact, four perforate genital plates, and one imperforate. Ambulacra sub-petaloid, pores unigeminal, the outer pore elongated in the sub-petaloid part. Interambulacra] plates wide, tubercles small. Peristome oval or pentagonal, excentric, a little anterior. Periproct placed in a sulcus on the dorsal surface. Inferior Oolite to present day. Ex. N. scu- tatus, Corallian. Clypeus. Test large, flattened, more or less discoidal, with circular or pentagonal outline, and flat or concave base. Apical disc small. Ambulacra large, petaloid, pores unigeminal (except near the peristome), outer pore elongated and in a long groove. Peristome nearly central, with a floscelle. Periproct on the dorsal surface, often in a sulcus. Tubercles very small. Inferior Oolite to Corallian. Ex. C. ploti, Inferior Oolite. CatopygUS. Test small, oval, elevated, truncated behind, with flat base. Apical disc small. Ambulacra sub-petaloid, uni- geminal, outer pore elongated in the sub-petaloid parts. Tubercles very small. Periproct high up on the posterior end. Peristome a little excentric, small, with a floscelle. Cretaceous to present day. Ex. C. colwnbarius, Upper Greensand. Collyrites (fig. 47 C). Test ovoid, inflated. Apical disc greatly elongated ; at the anterior end are four perforated genital plates separated by two oculars, at the posterior end are two oculars ; these two groups of plates are connected by numerous small plates. Ambulacra simple, pores unigeminal. The three anterior ambulacra meet at the anterior end of the apical disc, the other two meet at the posterior end. Interambulacra broad, tubercles small. Peri- stome excentric. Periproct above the posterior margin. Upper Lias to Cretaceous. Ex. C. bicordata, Corallian. ECHINODERMA. ECHINOIDEA 131 Echinocorys ( = Ananchytes) (fig. 47 B). Test very convex above, inferior surface flattened, outline oval. Apical disc a little elongated ; the four genital plates perforated, the two anterior sepa- rated from the two posterior by two large ocular plates. Ambulacra simple, pores unigeminal. Interambulacral plates large, tubercles small. Peristome anterior. Periproct oval, infra-marginal. Upper Chalk. Ex. E. vulgaris. Fig. 52. Holaster subglobosus, Chalk. Upper and lower surfaces. V 2 x -s. Holaster (fig. 52). Test heart-shaped, inferior surface more or less flattened, superior surface with a broad shallow groove in front. Apical disc elongate, the two pairs of genital plates separated by two oculars. Ambulacra large, simple ; pores uni- geminal, round or elongate ; the anterior ambulacrum in the groove. Interambulacra with small tubercles and granules. Peristome near the anterior margin, elliptical. Periproct supra-marginal. Upper Greensand and Chalk ; also Tertiary in Australia. Ex. H. sub- globosus, Lower Chalk. Cardiaster. Form similar to Holaster, but anterior groove usually with sharp borders. Apical disc similar to Holaster. Pores elongate, unigeminal. Small perforate and crenulate tubercles. Peristome near the anterior margin, with a projecting lip. Periproct on the posterior truncated end. Fasciole passes beneath the periproct and round the margin of the test. Cretaceous. Ex. C. ananckytis, Chalk, 9—2 132 ECHINODERMA. ECHINOIDEA Micraster (figs. 50, 53). Test heart-shaped or oval. Apical disc small, excentric. Ambulacra sub- petaloid, placed in sunken areas, the sub-petaloid parts of the two an- terior lateral longer than those of the two posterior lateral ; pores unigemi- nal. The anterior unpaired ambu- lacrum in a deep groove, with its pores circular. Interambulacra with large plates ; tubercles small, per- forate and crenulate. Fasciole below the anus. Peristome near the anterior border, with a projecting lip. Peri- proct on the upper part of the posterior end. On the under surface the pos- terior interambulacrum bulges out forming a plastron. Middle and Upper Chalk ; also Tertiary in Australia. Ex. M. cor-anguiiium, Upper Chalk. Hemiaster. Form similar to Micraster. A peripetalous fasciole only. Cretaceous to present day. Ex. H. bailyi, Gault. Schizaster. Test heart-shaped, highest behind, with excentric apex. Anterior ambulacrum long, placed in a groove; other ambulacra petaloid and in deep grooves — the posterior pair much shorter than the antero-lateral pair. Peristome near the anterior margin, with projecting lip. Periproct on the posterior truncated end of the test. A peripetalous fasciole, and usually also a lateral fasciole diverging from the former and passing beneath the periproct. Eocene to present day. Ex. S. cFurbani, Bracklesham Beds. ^ea; Fig. 53. Micraster cor-bovis. Upper Chalk, x \. Distribution of tlie Echinoidea Some echinoids live at great depths in the ocean, no less than a dozen species having been found below the 2000 fathom line, and one even at 2900 fathoms ; but by far the larger number occur near the coasts in shallow water: thus, of the 297 existing species recorded by Agassiz, 201 are found in water of less than 150 fathoms in depth. Echinoids are most abundant where the sea- ECHINODERMA. ECHINOIDEA 133 bottom is rocky, sandy, or calcareous, and less common where it is muddy ; consequently fossil forms are rare in clayey strata. Those found in deep water have a much wider range in space than those found in shallow water. Many genera, especially those with a considerable range in depth, have also a long range in time, some extending back to the Cretaceous or even earlier periods. Among the forms found in the Cretaceous which are still existing in deep water may be mentioned Salenia, Cottaldia, Hemiaste?', and Pygaster. The Palaeozoic echinoids belong to the regular group ; they are remarkable for possessing more than twenty columns of plates in the corona (except in Bothriocidaris), and frequently the plates overlap, rendering the test flexible. Echinoids are rare in Palaeozoic formations, especially in those of pre-Carboniferous age. The earliest form is Bothriocidaris, from the Ordovician rocks of Esthonia in Russia. In the Silurian, Echinocystis, Palceodiscus and Palceechinus are found; in the Devonian, Lepidocentrus ; in the Carboniferous, Palceechinus, Melonechinus (= Melo- nites), Perischodomus, and Archteocidaris. Primitive Cidaridas are common in the Trias of St Cassian and Bakony. In the Jurassic rocks the echinoids are much more numerous, relatively to the other groups of animals, than in the earlier formations ; they are comparatively rare in the Lias and the other clayey divisions, but very abundant in the calcareous beds, especially in the Inferior Oolite and the Corallian. In the Lias the chief forms are Cidaris,Hemi- pedina, Diademopsis, Pseudodiadema, and Acrosalenia; irregular echinoids (viz. Holectyp us, Collyrites, and Galero- pygus) make their first appearance in the Upper Lias. The genera which are best represented in the Middle and Upper 134 ECHINODERMA. ECHINOIDEA Jurassic are, of the regular group, Gidaris, Hemicidaris, Acrosalenia, Pseudodiadema, Diplopodia, Hemipedina, and Stomechinus ; of the irregular group, Gollyrites, Clypeus, Pygurus, Hyboclypeus, Nucleolites (= Echinobrissus), Ho- lectypus, and Pygaster. In the Cretaceous the echinoids are even more abundant than in the Jurassic, and attain their greatest development in the upper division of the system ; many of the genera found in the Lower Cretaceous occur also in the Upper Jurassic, but the irregular forms are more numerous than hitherto. The most important genera are, (1) regular, Cidaris, Pseudodiadema, Phymosoma (= Gyphosoma), Pel- tastes, Salenia ; (2) irregular, Discoidea, Galerites (= Echi- noconus), Hemiaster, Micraster, Gardiaster, Holaster, Echinocorys (= Ananchytes). Between the Cretaceous and the Eocene there is, in Britain, a great break in the succession of the echinoids ; not a single species is common to the two systems, and most of the genera also are different. This change is due in part to the great difference in the conditions under which the deposits were formed, the Chalk being a comparatively deep-water formation, and the Eocene beds, shallow water ; but the Eocene forms differ much more from those of the Upper Chalk than from those of the Chalk Marl, the latter deposit having been formed in water of less depth. Throughout the English Tertiaries the echinoids are much rarer than in the Cretaceous; thus in the Cretaceous there are thirty genera, in the Eocene seven, in the Pliocene eleven. In the Eocene this can be accounted for largely by the fact that the sea-bottom was for the most part muddy ; in the Pliocene, by the lower temperature of the ocean. The London Clay echinoids belong to tropical or sub-tropical genera. The commonest forms in the Eocene ECHINODERMA. ECHINOIDEA 135 of England are Hemiaster and Schizaster. In the Eocene of the South of Europe, India, etc., echinoids are numerous ; the regular forms are less important than in earlier forma- tions, but the Atelostomata,in this and subsequent deposits, become increasingly abundant. The Pliocene echinoids found in East Anglia show considerable affinity to those now living in the West Indian seas ; the principal genera represented are Echinus, Echinocyamus, Spatangus, and Temnechinus. CLASS IV. HOLOTHUROIDEA This Class includes the sea-cucumbers. They possess an elongated and usually cylindrical body with the mouth at one end and the anus at the other ; around the mouth is a circle of tentacles, which are really modified tube-feet. From the water- vascular ring five radial vessels are given off, and branches also go to the tentacles. In Synapta and its allies tube-feet (with the exception of the tentacles), as well as radial vessels, are absent. The stone-canal in almost all cases opens into the body- cavity. The integument is leathery, and the skeleton is very poorly developed, con- sisting of minute isolated „ . , , Fig. 54. A, B, anchor and plate of pieces of various shapes, such Synapta tenera, Recent. C, wheel as spicules, anchors, and ot Chirodota coiwexa iiom the r Inferior Oolite. Enlarged. wheels (fig. 54). At the present day the Holothurians are widely dis- tributed, but owing to the nature of their hard parts they are rarely found fossil. The earliest known forms occur in the Carboniferous rocks of Scotland, and a few specimens have been recorded from Jurassic and later formations. 136 ECHINODERMA. PELMATOZOA II. PELMATOZOA The Pelmatozoa, unlike the Eleutherozoa, are generally sedentary, being attached to the sea-floor or some foreign object by the aboral surface, usually by means of a jointed stem ; in most cases the attachment is permanent, but it may be temporary only. The group is essentially dis- tinguished by the ciliated grooves which radiate from the mouth ; the cilia produce a current of water which carries small organisms to the upwardly directed mouth. The Classes of the Pelmatozoa are: (1) Crinoidea, (2) Cystidea, (3) Blastoidea, (4) Edrioasteroidea. CLASS I. CRINOIDEA The Crinoidea include the sea-lilies and feather-stars. The skeleton consists of a stem, a calyx, and movable arms given off from the margin of the calyx (fig. 55). The calyx is more or less globular, or cup- or basin- shaped, and contains the digestive and other important organs ; the mouth is either at or near the centre of the ventral or oral surface, and the anus, which is excentric and inter-radial, is also on the oral surface, and is usually situated at the end of a tubular process. There is a groove on the ventral surface of each arm, and these grooves — the food-grooves — are continued over the oral surface to the mouth ; they are lined with cilia, by the movements of which food is conveyed to the mouth. There are generally five arms, but each may branch repeatedly. Immediately under the groove of each arm there is a radial nerve-cord ; these cords unite to form larger trunks and ultimately join as a ring round the mouth. Beneath the nerve of each arm is a radial vessel of the water- vascular system, which is continued over the oral surface and joins a ring round the ECHINODERMA. CRINOIDEA 137 mouth ; from this ring tubes hang down and open into the body-cavity, which communicates with the water of the exterior by means of pores. In connection with the radial vessels are tubular processes, the tentacles, which form a row on each side of the food-grooves, and correspond with the tube-feet of the star-fish, but do not function in locomotion. In addition to the nervous system already mentioned, there is another supplying the aboral elements of the skeleton ; from a centre at the aboral pole of the calyx nerve cords are given off, which pass through canals in the plates of the calyx to the arms and pinnules, and also into the stem when present. The stem (figs. 55, 57, a) in the crinoids is more or less flexible, and is sometimes several feet in length. It con- sists of a number of segments, known as columnals, which may be in the form of circular or pentagonal (occasionally square or elliptical) plates ; or they may be higher than broad, forming cylinders; these columnals articulate by their flat surfaces, which are often provided with radiating striae or with ridges in the form of a rosette. Each columnal is pierced at the centre by a canal which is circular or pentagonal and contains a prolongation of the aboral nervous system and vascular organ. From the stem small branches known as cirri are sometimes given off; these have a structure similar to that of the stem, and are also pierced by a central canal. The columnals are generally of different heights — larger plates being separated by smaller ; the former are first developed, and the latter subsequently introduced between them. Cirri are borne on some of the larger columnals. The lower end of the stem may taper, but often expands and branches, forming a root-like structure which serves to fix the animal. The part of the calyx below the origin of the free arms Fig. 55. Botryocrinus decadactylus, from the Wenlock Limestone — a simple form of Crinoid, seen from the posterior inter-radius. (From the Guide to the Geol. Bept., Brit. Mus.) Natural size. ECHINODERMA. CRINOIDEA 139 is called the dorsal cup (fig. 55) ; the part above them is the teg men. The dorsal cup consists at its base of a cycle of five plates, known as basals (figs. 56, b ; 57, c) ; but, owing to fusion, the number of basals is sometimes reduced to four, three, or rarely two. In some forms there is below the basals and alternating with them another row of plates (five or three), termed infra-basals (fig. 57, b), and the base is then said to be dicyclic ; when basals only are present, it is monocyclic. Above the basals, and alter- nating with them, is a cycle of five radial plates (fig. 56, r ; fig. 57, d). In some genera there are, between the two posterior radials, other plates, the anal inter-radials (fig. 56, a ; fig. 57, e). The arms are characteristic of the Crinoidea; they come off directly from the radials, and are formed either of a single or of a double row of plates, the brachials ; when there is a single row the arm is termed uniserial ; when there are two rows it is biserial. In biserial arms the plates alternate with one another. The dorsal or outer surface of the brachial plates is rounded; on the ventral or inner surface there is a groove in which the soft parts, above described, are placed ; and there is usually also a perforation below the groove, in which the dorsal nerve- cord is situated. The groove in the arms is covered over by a series of plates — the covering plates, which can be opened and closed, and serve for the protection of the soft parts. Where an arm branches, the brachial which sup- ports two branches (figs. 55, 57) has sloping sides, and is known as an axillare. Small unbranched appendages called pinnules occur on the arms of many crinoids (fig. 55); they are similar in structure to the arms, and are given off alternately on opposite sides. In living crinoids the genital products mature in the pinnules. In some forms, 140 ECHINODERMA. CRINOIDEA the earlier rows of brachial plates become firmly united to one another and to the radials (figs. 56, 58, 2, 3, br) ; these fixed brachials have often been regarded as radials, but morphologically they are only brachials which have become incorporated into the calyx. The fixed brachials may be in contact at the sides, or, as in most Palaeozoic crinoids, they may be separated by other plates which are termed inter -brachials (fig. 56, ir). In the posterior inter- radial area (that which leads up to the anus) the inter- brachial plates are often more numerous than in the other areas. When a stem is absent there is often a central plate at the base of the calyx {e.g. Marsupites). The tegmen or oral surface of the calyx is usually more or less completely covered by calcareous plates. Sometimes five large triangular plates (orals) only occur, between which are the food-grooves ; but usually other smaller plates are also present — the food-grooves being usually covered by plates, sometimes called " ambulacrals," and between them occur numerous " interambulacral" plates. In many Palaeozoic crinoids (e.g. Actinocrinus) the tegmen consists of a complete vault or dome of stout plates concealing the mouth as well as the food-grooves and their covering plates; commonly this plated tegmen extends upwards around the anal process forming a tube- like covering. In the genera described below, the basals, radials, and arms are five in number unless otherwise stated. A. Monocyclic Crinoids Platycrinus. Basals three, unequal. Radials large. Some fixed brachials. One inter-brachial in each area — more in the posterior (anal) area. No inter-radial. Arms bifurcating once to thrice, uniserial at the lower end, biserial above ; pinnules long. ECHINODERMA. CRINOIDEA 141 Tegmen with small plates ; anus sub-central, sometimes at the end of a long process. Stem long, section often elliptical. Devonian, but mainly Carboniferous. Ex. P. Icevis, Carboniferous Limestone. Eucalyptocrinus ( = Hypantkocrinus). Calyx deeply con- cave at the base ; at the bottom of the cavity four basals, at the sides five radials ; several cycles of fixed brachials, and some inter- brachials. Tegmen elevated, and forming a central anal tube com- posed of five rows of large plates. Ten vertical partitions spring from the outside of the tegmen, forming compartments in which the ten arms rest. Arms biserial except at the base. Silurian and Devonian. Ex. E. decorus, Wenlock Limestone. Actinocrinus (fig. 56). Calyx pear-shaped, ovoid, or more or less spherical. Basals three, equal, forming a hexagon. Radials OP* <3 &QO Fig. 56. Diagram of the plates of Actinocrinus triacontadactylus, Carboni- ferous Limestone, b, basal plates ; r, radials ; 2, 3, fixed brachials ; br, brachial plates ; ir, inter-brachials ; a, anal inter-radial. generally higher than wide. The first two rows of brachials firmly united. Inter-brachials numerous ; and also one (posterior) inter- radial, above which the inter-brachials are more numerous than in the other areas. Tegmen formed of thick, tubercled, hexagonal plates, produced into a tube with the anus at the end. Arm- branches ten to thirty, biserial. Stem circular, canal pentagonal. Carboniferous. Ex. A. triacontadactylus, Carboniferous Limestone. 142 ECIIINODERMA. CRINOIDEA Amphoracrinus. Related to Actinocrinus. Calyx depressed, saucer-like or nearly flat. Tegmen much elevated. Three basals, and a posterior inter-radial. Inter- brachials few. Anal tube short, excentric. Carboniferous. Ex. A. amphora. B. Dicyclic Crinoids Cyathocrinus (fig. 57). Calyx cup-like. Infra-basals small, equal, pentagonal. Basals large, hexagonal (except the posterior, which is heptagonal and supports the square inter-radial plate). Radials shield-shaped. Arms uni- serial, very long, bifurcating from five to seven times, without pinnules. Tegmen produced into a long anal tube. Stem round, without cirri. Silurian to Carboni ferous. Ex. C. longimanus, C. acinotubus, Silurian. Fig. 57. Cyathocrinus longimanus, from the Silurian, a, portion of stem ; b, infra-basal plates ; c, basals ; d, radials ; e, anal inter- radial ; /, first brachial. Re- duced. Crotalocrinus. Dorsal cup similar to that of Cyathocrinus. Some fixed brachials present. Arms uniserial, dichotomous, the branches uniting so as to form lamellar expansions or networks ; pinnules absent. Tegmen nearly flat, formed of small plates with five large plates at the centre. Anus near the posterior margin. Stem thick, circular ; canal pentagonal ; roots thick. Wenlock Limestone. Ex. C. rugosus. Botryocrinus (fig. 55). Calyx small, cup-shaped. Infra- basals pentagonal ; basals hexagonal (except the two posterior, which are pentagonal) ; radials with the articular surface occupying ^ to | of the width ; two anal inter-radials, one as in Cyathocrinus, another below it on the right. Arms divide, giving ten main branches which often bear smaller branches or pinnules. Anal tube large, sometimes ECHINODERMA. CRINOIDEA 143 coiled, anus near its base. Stem formed of low plates, often in five pieces. Silurian and Devonian. Ex. B. decadactylus, Wenlock Limestone. Poteriocrinus. Calyx with thin plates. Infra-basals equal. Basals high. Three anal inter- radials present. Radials with well- marked concave articular surfaces which do not occupy the entire width of the plates. Anal tube long. Arms long, branching, with pinnules. Devonian and Carboniferous. Ex. P. granulosus, Car- boniferous. Woodocrinus. Allied to Poteriocrinus but calyx, arms, and anal tube shorter. Carboniferous. Ex. W. macrodactylus. Encrinus. Calyx saucer-shaped. Infra-basals very small, generally concealed by the stem. Basals rather large, hexagonal. Radials large, pentagonal. Two fixed brachials in each ray, the upper being axillary. No inter-brachials. Arms bifurcating, the branches uniserial at first, then alternating, finally biserial ; with pinnules. Tegmen covered with plates. Stem long, with small canal. Trias. Ex. E. liliiformis, Muschelkalk. Pentacrinus. Calyx small, bowl-shaped, consisting of small infra-basals, basals, and radials which projeot like spines over the stem. Arms very long, much branched, uniserial ; the small branches all come off on the same side of each main branch. The arms bear pinnules. Stem long, pentagonal, with cirri coming off in whorls ; the articular surfaces of the columnals with five raised, crenulate, petaloid parts which are narrow and quite distinct from one another. Jurassic. Ex. P. fossilis, Lias. Marsupites. Calyx large, globular ; plates large and thin. Stem absent. Base formed of a large central pentagonal plate. Infra-basals pentagonal. Basals hexagonal. Radials pentagonal, with crescentic depressions for the articulation of the arms. Arms relatively short, bifurcating, uniserial. Upper Chalk. Ex. M. testu- dinarius. Ichthyocrinus. Three very small infra-basals ; five small basals ; five radials ; two or three cycles of fixed brachials. Anal inter-radial small, below the right posterior radial. Arms in contact all round, uniserial ; no pinnules. Silurian to Carboniferous. Ex. 1. piriformis, Silurian. 144 ECHINODERMA. CRINOIDEA Sagenocrinus. Infra-basals small. Anal inter- radial sunk between basals ; radials large. Numerous cycles of fixed brachials, separated by very numerous inter-brachials. Arms dividing, uni- serial ; no pinnules. Silurian. Ex. S. expansus. Apiocrinus (fig. 58). Calyx large. Infra-basals enclosed by, and often fused with, the thick basals. Radials low, excavated on their upper surfaces. Four cycles of fixed brachials. Arms ten, bifurcating once or twice, uniserial. Stem long, cylindrical, base expanded ; the articular surfaces of the columnals radi- ately striated. The upper colum- nals are in contact at the periphery only. The upper part of the stem expands and passes gradually into the calyx ; the upper surface of the last columnal is provided with five radiating ridges between which the basals lie. Lias to Lower Cretaceous. Ex. A. kinsoni, Bradford Clay. par- Fig. 58. Apiocrinus parkinsoni, from the Bradford Clay, s, top columnal of the stem ; /;, basal plates ; r, radial plates ; 2, 3, and br, fixed brachial plates. Millericrinus. Allied to Apiocrinus. Usually the top columnal only is widened. Articular facets of radials and brachials well developed. Lias (1 also Trias) to Lower Cretaceous. Ex. M. pratti, Inferior and Great Oolite. Bourgueticrinus. Calyx small, with vertical or inwardly- sloping sides ; basals about half the height of radials ; two rows of fixed brachials ; no inter-brachials. Free arms unknown. Stem long, the top columnal very large, as wide as calyx ; upper columnals with circular, others with elliptical articular faces and a transverse ridge across the longer diameter. Cretaceous. Ex. B. ellipticus, Chalk. ECHINODERMA. CRINOIDEA 145 Distribution of the Crinoidea In comparison with the large number of genera which existed in past ages, especially in the Palaeozoic period, the Crinoidea are but poorly represented at the present day. The most important families are the Antedonidse and the Actinometridae ; these are widely distributed, and occur chiefly in shallow water, but some are found at con- siderable depths — Antedon extending from the shore-line down to 2900 fathoms, and Actinometra down to 800 fathoms. The stalked crinoids (e.g. Isocrinus, Rhizocrinus) are much less abundant than the Antedonidse and Actino- metridae, and are found mainly at great depths. In most cases the species of crinoids have only a limited distribu- tion in space. In the Palaeozoic formations the crinoids are much more numerous than the other Echinoderms, their remains (chiefly stems) forming the main part of some limestone beds (crinoidal limestone or marble), as for instance in the Carboniferous. The other Echinoderms are seldom suffi- ciently numerous to be of importance as rock-builders. The majority of fossil crinoids appear to have lived in fairly shallow water, since they are found in association with reef-building corals and other shallow-water organisms. Crinoids occur first in the Tremadoc Beds. In the Ordo- vician, Glyptocrinus, Dendrocrinus, and a few others have been found. In the Silurian, crinoids become very much more abundant, and attain their maximum development ; the most important genera are Botryocrinus, Calceocrinus, Or otalo crimes, Eucalyptocrinus, Gissocrinus, Ichthyocrinus, Marsipocrinus, Periechocrinus, Pisocrinus, Sagenocrinus, Taxoorinus. In the Devonian, Cyathocrinus, Cupresso- crinus, Haplocrinus, Hexacrinus and others are common ; w. p. 10 146 ECHINODERMA. CRINOIDEA in the Carboniferous, A ctinocrinus, Amphoracrinas^Poterio- crinus, Platycrinus, Rhodocrinus, and Woodocrinus. Crinoids are rare in the Permian. Throughout the Mesozoic form- ations they are much less abundant than in the Palaeozoic ; in the Trias the characteristic form is Encrinus. In the Jurassic, Antedon, Isocrinus, Pentacrinus, Saccocoma, Apiocrinus, and Millericrinus are found, the first two living on to the present day. In the Cretaceous the chief forms are Marsupites, Uintacrinus, and Bourgueticrinus. In the Cainozoic, crinoids are very rare. CLASS II. CYSTIDEA The stem in the Cystideans is short, and in some cases absent. The calyx is usually more or less spherical or ovoid, and varies considerably in structure in different types; frequently the plates are very numerous, without radial symmetry, and perforated by numerous canals ; food-grooves usually extend from the mouth over the surface of the calyx, and bear simple arm-like structures, called brachioles (fig. 60). In Glyptosphwra (fig. 59 A), from the Ordovician, the calyx is spherical, and composed of a very large number of polygonal plates, which are without any radial arrange- ment such as occurs in the Crinoids and Blastoids. The mouth is at the summit of the calyx, and is covered by five oral plates (a), between which the five food-grooves start and extend in a radial manner over the upper part of the calyx, sometimes giving off branches (b) ; at the ends of these grooves are facets (c) to which the brachioles were articulated. The grooves were protected by small covering- plates. On one side of the calyx is the anus (d), which in perfect specimens is covered by a pyramid of small ECHINODERMA. CYSTIDEA 147 triangular plates. Between the mouth and the anus is the madreporite (e), which is the external opening of the water- vascular system; just below it is the small, circular genital aperture. All the plates of the calyx are pierced by canals running perpendicularly to the surface ; the canals are in pairs, and the external openings of each pair are enclosed in a raised or depressed area of oval shape (fig. 59 B). b — Fig. 59. A, Glyptosphcera leuchtenbergi, from the Ordovician of Russia. a, mouth covered by oral plates ; b, food-grooves ; c, facet for the brachiole ; d, anus ; e, just above this is the triangular madreporite, just below is the circular genital aperture (after Volborth). B, a few plates of the same enlarged, showing the pairs of pores. C, plates of Echinosphcera, with pore-rhombs, enlarged. Some Cystideans are more primitive in character than the form just described. For example, Aristocytis, from the Ordovician of Bohemia, has an ovoid or pear-shaped body formed of numerous plates, but possesses no food- grooves, brachioles, or stem, and the pores traversing the plates are single. In another group of the Cystidea the plates of the calyx are traversed by canals which are arranged in groups 10—2 148 ECHINODERMA. CYSTIDEA having a rhombic form ; one half of each rhomb is on one plate, the other on an adjoining plate (fig. 59 C). The canals are parallel to the surface of the plates, and perpen- dicular to the sutures between the plates. These groups of canals are known as pore-rhombs. Echinosphcera, from the Ordovician, is a form which possesses many pore-rhombs; it has a spherical calyx, consist- ing of numerous plates, some of which project at the base and probably served to fix the calyx, there being no stem ; around the mouth are from three to five small arms. In most genera belonging to this group the plates of the calyx are much fewer in number than in Echinosphcera, and have a distinctly radial sym- metry— being arranged in cycles, the plates of each cycle alternating with those immediately below ; for ex- ample, the calyx of Lepado- crinus, from the Silurian (fig. GO), is formed of five cycles of plates ; at the base is a cycle of four plates, followed by four cycles of five plates each; from the summit of the ovoid calyx four food-grooves stretch to- ward the base ; they do not rest directly on the calyx, as is the case in Glyptosphcera, but on specially-developed plates. Numerous brachioles Fig. 60. Lepadocrinus quadri- fasciatus, from the Wenlock Limestone. Restored figure. The brachioles of the outer rows are erect ; those of the middle row depressed. Near the top of the left-hand quarter is the anus ; near the top of the right- hand quarter is a pectini- rhomb. (From the Guide to the Geol. Dept., Brit. Mus.) Natural size. ECHINODERMA. CYSTIDEA 149 come off from each side of the food-grooves. In this genus there are only three rhombs, and they are of the more highly-developed type called pectini-rhombs, which differ from pore-rhombs in being surrounded by a raised rim and in having the folds of the plate more pronounced. In some other Cystideans of this group the brachioles are found near the mouth only. Distribution of the Cystidea The Cystideans are comparatively rare fossils. They range from the Middle Cambrian to the Carboniferous Limestone, and attain their maximum development in the Upper Ordovician. In the Menevian, Protocystis is found ; this also occurs in the Tremadoc Beds, and with it Macro- cy stella. In the Ordovician, Aristocystis, Ecliinosphaira, Pleurocystis, Glyptosphcera and others are present ; in the Silurian, Lepadocrinus, Pseudocrinus, and Placocystis, In the Devonian there are fewer forms, and from the Carboniferous only one or two genera have been recorded. CLASS III. BLASTOIDEA In the Blastoids (fig. 61) the body consists of a calyx, usually with a stem ; but the latter is rarely found attached to the calyx. The calyx may be spherical, oval, pear-shaped, or bud-like ; in most cases it is formed almost entirely of thirteen plates, arranged in a regular manner. True arms are not present. Pentremites is the commonest Blastoid, and may there- fore conveniently be taken as an example of the group. Its calyx (fig. 62) has the following structure. The aboral part is formed of a cycle of three plates — the basals (b), two of which are alike, and the third smaller. Above the basals is a cycle of five radial plates (r) ; these are 150 ECHINODERMA. BLASTOIDEA Deltoids m§&$ Radials w Basals tw if mmv y Brachioles >■ Calyx V Stem J y Root Fig. 61. Orophocrinus fusiformis, from the Carboniferous of Iowa. Restored figure. (From the Guide to the Geol. Dept., Brit. Mus.) Natural size. ECHINODERMA. BLASTOIDEA 151 larger than the basals, and form the main part of the calyx. At the upper end of each there is a deep incision, which serves for the reception of the food-carrying area (a); this is usually spoken of as an " ambulacrum," but there is no evidence of the existence of a radial water vessel, and it is doubtful whether this area is really homologous with the ambulacrum of an Echinoid. Above the radials and alter- nating with them occur five smaller plates — the deltoids (d) or inter-radials. The mouth is placed at the summit of the calyx, in the centre, and around it are five other B -- s r Fig. 62. Pentremites godoni, Carboniferous. A, side ; B, upper surface ; C, under surface. a, ambulacra ; b, basal plates ; r, radials ; d, deltoids ; s, spiracles around the mouth ; an, anus, x 2. openings termed spiracles (s), one of which is larger than the others and includes the anus (an). From the mouth the five ambulacra (a) radiate towards the aboral surface, and are bordered partly by the deltoids but mainly by the radials. Each ambulacrum (fig. 63) consists of the following plates : in the middle is a long pointed plate (I), the lancet-plate, which is traversed by a longitudinal canal, in which a nerve may have been present. On each side of the lancet-plate is a row of 152 ECHINODERMA. BLASTOIDEA p- small plates, the side-plates (s). Extending down the middle of each ambulacrum is the food-groove (a), which, in perfect specimens, is l covered over by small plates. At right angles to this groove, on each side of it, are numerous transverse grooves. Along the outer margin of the side-plates there is a row of pores, the marginal pores (p), formed by spaces between adjoining plates. Beneath each ambu- lacrum are two hydrospires (fig. 64, h), one on each side. The hydrospire (fig. 65) is a flattened and folded organ, communicating with the exterior by means of the marginal Fig 63. Ambulacrum of Pen- tremites godoni, Carboniferous. I, lancet-plate; s, side-plate; p, pore ; a, food-groove ; sp. spi- racle, x 3. Fig. 64. Fig. 65. Fig. 64. Pentremites sulcatus, Carboniferous. Horizontal section of the calyx. I, lancet-plate ; p, side-plates ; r, radial plates ; h, hydrospires (not quite correctly drawn, see fig. 65). (After Zittel.) Enlarged. Fig. 65. Pentremites, Carboniferous. Section across ambulacrum, br, brachiole ; cp, covering-plates ; L, lancet-plate ; osp, outer side-plate ; R, radial ; si, sub-lancet-plate ; sp, side-plate. (After Bather), x 5. ECHINODERMA. BLASTOIDEA 153 pores, and also by the spiracles on the oral surface of the calyx. A current of water probably passed in through the former openings and out by the latter. In well-preserved specimens the mouth, as in many crinoids, is not visible externally, but is covered over by a roof of small plates. From the margins of the ambulacra pinnule-like append- ages known as brachioles (fig. 61) are given off; these are seldom preserved, but pits or facets to which they were attached are seen on the side-plates. The hydrospires are really folded parts of the radial and deltoid plates — the folds being parallel to the margin of the ambulacra. This is seen clearly in Codaster, which is a more primitive form than Pentremites ; in that genus (fig. 66) the folds open directly to the exterior by slits, br. c.p. s.p^y R.pr. rOSPL Fig. 66. Fig. 67. Fig. 66. Codaster trilobatus, Carboniferous. Section across ambulacrum. (After Bather.) x 5. Fig. 67. Phcenoschisma verneuili, Carboniferous. Section across ambu- lacrum. (After Bather.) Enlarged. br, brachiole ; cp, covering-plate ; L, lancet-plate ; osp, outer side- plate ; R, radial ; Rpr, part of radial ; sp, side-plate. owing to the fact that they are not covered by the lancet- plate and side-plates ; and on account of this circumstance spiracles are not developed. In some genera, in which the folds are concealed (fig. 67), the space below the lancet-plate and side-plates, into which the folds open, communicates with the exterior at the oral end by slits 154 ECHINODERMA. BLASTOIDEA or incipient spiracles. A further modification is seen in Pentremites (fig. 65) in which, owing to the hydrospire being pushed further into the cavity of the calyx, the folds open into a common canal instead of into the space between the summits of the folds and the overlying lancet- plate and side-plates ; this canal opens orally by true spiracles (fig. 62 B, s). The number of folds in each hydrospire varies from one to nine. In a few primitive types hydrospires are absent. In many Blastoids there are five pairs of spiracles and an independent anus, but in some genera {e.g. Pentremites) the pairs are confluent so that only five spiracles are present, of which the posterior encloses the anus. The ambulacra vary in width and length ; they may be broad and petaloid or narrow and linear. In some genera the alternate side-plates become squeezed towards the outside of the ambulacrum ; here they form an outer row, known as the outer side-plates, and are smaller than the plates of the inner row. The side-plates may be entirely at the sides of the lancet-plate (fig. 67), or they may rest on it and partly, or even completely, conceal it (fig. 66). The basals, radials, and deltoids vary considerably in relative size — thus the deltoids may be very small (as in Troostocrinns), or they may form a considerable part of the calyx (as in Orhitremites). The most important characters of the Blastoidea as a Class are found in the ambulacra and hydrospires, the absence of true arms, the monocyclic base consisting of three basals only, and the five incised radials. In a few rare cases, hydrospires have been found to be present in the Crinoidea {Carabocrinus, Hybocrinus). Codaster. Calyx in the form of an inverted cone or pyramid. Basals forming a conical and usually deep cup ; radials large, with ECHINODERMA. BLASTOIDEA 155 the forked parts sharply bent, forming part of the flattened upper surface of the calyx ; deltoids and ambulacra confined to upper surface. A long lancet-plate, with side-plates, occurs between the deltoids and radials. Hydrospires consist of sharp folds of the calyx where the radials and deltoids meet, and open at the surface by slits. Mouth pentagonal, originally plated over ; no spiracles ; anus between the posterior deltoid and radials. Silurian to Carboni- ferous. Ex. C. trilobatus, Carboniferous. Orbitremites { = Granatocrinus). Calyx elliptical, ovate, or more or less spherical, in section pentagonal or round ; with concave base. Basals small, not seen in a side view. Radials of variable size and forming part of the base. Deltoids generally rhombic, large in some species, small in others. Ambulacra narrow, straight, with nearly parallel sides. Lancet-plate narrow. Hydrospires simple, usually with two or three folds only, dilated at the free ends ; the inner fold forms a plate next to the lancet-plate. Spiracles five, round or oval, piercing the apices of the deltoids, the posterior one including the anus. Carboniferous Limestone. Ex. 0. derbiensis. Distribution of the Blastoidea In England the Blastoids range from the Devonian to the Carboniferous, being most abundant in the latter. A few primitive types (Asteroblastus, Blastoidocrinus) occur in the Ordovician of Russia and Canada ; and some others (Troostocrinus, Codaster) are found in the Silurian of North America. The English Devonian forms are rare and but little known. In the Carboniferous Limestone the blastoids attain their maximum development ; ten genera are represented, the most important being Codaster, Orophocrinus, Schizoblastus, Orbitremites and Mesoblastus. Pentremites is common in the Carboniferous of America, but is not found in Britain. 156 ECHINODERMA. EDRIOASTEROIDEA CLASS IV. EDRIOASTEROIDEA The calyx in the Edrioasteroids (fig. 68 A) is usually composed of a large number of irregular plates, and in most cases is flattened and more or less circular in outline ; it is attached to some foreign body by the under part — a stem being very rarely present. The mouth is at the centre of the upper surface (ps), and is covered by plates ; from it five ambulacra extend outwards over the upper arnb Fig. 68. Edrioaster bigsbyi, Ordovician of Canada. (From Bather.) A, oral surface, amb, covering-plates over the anterior and left-anterior ambulacral grooves, but removed from the other grooves ; ad, floor- plates of ambulacral grooves ; p, pores between floor-plates ; ps, peri- stome, the greater part of which is roofed by enlarged covering- plates ; ia, interambulacrum ; M, madreporite ; As, anus. Natural size. B, section across the same specimen through the right anterior ambu- lacrum and the left posterior interambulacrum. Lettering as in A. /, frame of stouter plates ; m, membrane with overlapping plates thrown into five lobes (I). Natural size. C, section across an ambulacrum with covering-plates (amb) over the groove (vg). Enlarged. surface of the calyx, and sometimes over part of the lower surface also. The ambulacra do not branch, but are ECHINODERMA. EDRIOASTEROIDEA 157 frequently curved. The ambulacral grooves are covered by two rows of alternating plates (amb), similar to the covering-plates of crinoids. In Edrioaster and its near allies the floor of each groove is formed of special plates (ad), between or at the outer margins of which are pores (p) which may indicate the existence of tube-feet. Neither brachioles nor arms are developed in connexion with the ambulacra. The anus, which is covered by a pyramid of plates, as in the Cystidea, is on the upper surface — in the area between the two posterior ambulacra (As). The calyx was more or less flexible in some cases ; and frequently around its border on the upper surface (but sometimes on the lower, fig. 68 B, f) there is a series of larger marginal plates, forming a framework, which, in combination with the five conspicuous ambulacra, gives the upper surface something of the appearance of a star-fish in which the rays are not prolonged. The Edrioasteroids include only a few genera, and have usually been regarded as Cystidea, but differ in the absence of brachioles, and in the occurrence of pores between the flooring-plates, suggestive of the presence of an internal radial water vessel with tube-feet. Distribution of the Edrioasteroidea The Class ranges from the Cambrian to the Carbon- iferous, and is best represented in the Ordovician. The principal genera are : — Stromatocystis in the Cambrian ; Cyathocystis, Edrioaster and Steganoblastus in the Ordo- vician ; and Agelacrinus and Lepidodiscus, ranging from the Ordovician to the Carboniferous. PHYLUM ANNELIDA CLASS CH^TOPODA The Chaetopoda include various forms of worms. The body is segmented and generally the segments are similar. There is a ventral nerve-cord and a nerve-ring round the oesophagus connected with a pair of ganglia above it. A vascular system and a body-cavity (ccelom) are present. The Chaetopoda possess bristle-like processes termed setae which assist in locomotion. There are three orders, (1) the Archiannelida, e.g. Polygordius, (2) the Oligochaeta, e.g. the common earthworm Lumbricus, and (3) the Polychaeta. The Archiannelida and the Oligochaeta are unknown in the fossil state. The Hirudinea or leeches are regarded by some writers as a distinct Class of the Annelida, but by others as a division of the Chaetopoda; they do not occur fossil. ORDER III. POLYCH^TA The members of this Order are nearly all marine ; they are characterised by the possession of numerous setae, which are placed on special processes termed parapodia. Tentacles are usually present on the head. Many forms live in tubes, which may consist of carbonate of lime, of chitinous material, or of grains of sand cemented together by a secretion. On account of the possession of this tube ANNELIDA. CH^TOPODA 159 the polychsetous worms are often found fossil. Other forms, which do not live in tubes, are provided with minute chitinous jaws, and in some formations, especially the Ordovician and Silurian, these are abundantly pre- served. Serpula. Tube calcareous, long, round, angular or flattened ; straight, curved irregularly or sometimes spirally, closed at one end ; generally attached to some foreign object by a portion of its surface. Silurian to present day. Ex. S. gordialis, Chalk. Spirorbis. Tube calcareous, small, spiral, attached by one side. The spiral either left-handed or right-handed, the last whorl often produced into a free tube. Ordovician to present day. Ex. S. pusillus ( = carbonarius), Carboniferous. Distribution of the Chcetopoda Nearly all the worms which are found fossil belong to the Polychaeta; the earliest examples occur in the Cambrian Beds. In addition to worm-tubes and jaws, there are, in various rocks, numerous trails and burrows, which are con- sidered by some authors to have been formed by worms, but in many cases it is probable that they were made by other animals such as crustaceans and gasteropods. PHYLUM BRACHIOPODA Classes 1. Inarticulata 2. Articulata Orders Atremata. Neotremata. Protremata. Telotremata. In the Brachiopods the soft parts of the animal are en- closed in a shell which is formed of two parts termed valves, one placed on the dorsal surface, the other on the ventral. Generally the main part of the body occupies only the pos- terior portion of the shell. The interior of the shell is lined by a membrane, the mantle, which is a prolongation of the body-wall, and is divided into two lobes, one oc- curring in each valve ; the space between the two is known as the mantle-cavity. In most genera the margin of the mantle is thickened, and carries numerous chitinous setae. The mouth (fig. 69, v) opens into the mantle-cavity, and leads into an oesophagus, which is followed by a stomach (partly surrounded by the liver), and an intestine. In the articulate brachiopods the intestine is short and ends blindly, in the inarticulate forms it is long and ends in an anus which opens into the mantle-cavity. The nervous system consists of a ring round the oesophagus, with gang- lionic enlargements from which nerves are given off to the arms, mantle, etc. The part of the body-cavity which BRACHIOPODA 161 surrounds the alimentary canal communicates with the mantle-cavity by means of two, or rarely four, funnel- shaped canals, which serve as excretory organs. The body-cavity extends into the mantle as a series of spaces or sinuses ; these produce slight depressions on the interior of the valves, and can often be traced as ridges on the internal casts of fossil specimens (tig. 85). The body-cavity is filled with a fluid which is kept in motion by means of cilia. A vesicle found on the dorsal surface of the alimentary canal, near the oesophagus, is regarded as the heart. The brachiopods are never colonial animals. Repro- duction takes place sexually, and the sexes are separate. The genital organs are placed in the body-cavity, and in the sinuses of the mantle. Generally the greater part of the mantle-cavity is occupied by two long processes, given off from the sides of the mouth ; these are known as the " arms " (fig. 69, d), since they were at first supposed to serve in locomotion — hence the name Brachiopoda. The arms are covered with cirri (h), which produce a current of water conveying food to the mouth. Respiration is carried on mainly by the mantle, but possibly also to some extent by the arms. Of the two valves of the brachiopod, the ventral is nearly always larger than the dorsal ; each is produced Fig. 69. Magellania [ = Wald- heimia~\Jlavesceiis, Recent. Lon- gitudinal section. d, (upper), cardinal process ; d, (lower), arms ; h, cirri ; a, adductor muscles ; c, c', divaricator mus- cles ; ss, septum ; v, mouth ; z, terminal part of alimentary canal. (After Davidson.) x l|. w. p. 11 162 BRACHIOPOD A into a beak or umbo (fig. 70). The ventral umbo is more prominent than the dorsal, and has generally, either at its apex or just beneath it, an opening. With a very few exceptions the shell of the brachiopod is equilateral, that is to say, a line drawn from the umbo to the opposite margin divides it into two equal and similar parts. This character, combined with the inequality in the size of the valves and the perforation at the umbo, renders it easy to distinguish the shell of a brachiopod from that of a lamel- libranch. In many forms the two valves are joined together by means of a hinge, these constitute the group Articulata ; in others they are held together by the muscles Fig. 70. Terebratula semiglobosa, Upper Chalk. A, dorsal view. B, lateral view, a, posterior ; b, anterior ; a — b, length ; c — d, breadth ; e — -/, thickness ; g — h, hinge-line. x §. and the mantle only, these form the Inartioulata. The hinge consists of two short curved processes or teeth given off from the ventral valve near the umbo, which fit into corresponding sockets in the dorsal valve. In some genera (e.g. Orthis) the teeth are supported by plates (the dental plates) which are fixed to the inside of the ventral valve. The part of the margin of the valves where the teeth occur and on which the two valves move in the opening and closing of the shell, is termed the hinge-line (fig. 70, g — h). In some genera (Terebratula) this is short and curved, in BRACHIOPODA 163 others (Spirifer, fig. 82) it is long and straight. The posterior part of the shell is that near the hinge (fig. 70, a), the anterior is the opposite margin (b). The length of the shell is measured from the anterior to the posterior border (J) — a). The breadth is at right angles to this, from one side of the shell to the other (c — d). The thickness is measured from one valve to the other, perpendicular to the length and breadth (e—f). In some genera (e.g. Terebra- tula) the length is greater than the breadth, in others (e.g. Strophomena) the breadth is greater. Between the hinge- line and the umbo there is in some brachiopods (e.g. Cyrtia, fig. 71) a flat or slightly concave portion of the shell, usually triangular, on which the ornamentation of the rest of the shell is absent, the surface being either smooth _. _n _ Z~ t w ° . m Fig. 71. Cyrtia exporrecta, Wen- or Striated ; this is known as lock Limestone. a, umbo of ,i Ti. ventral valve : abc, area with the area. It may occur on deltidium in t'he m;ddle . &_Cj both valves (e.g. Ortllis), but hinge-line. Natural size. is sometimes found on the ventral valve only. Nearly all living brachiopods are fixed to a rock or other object ; but some fossil forms were free, especially in old age (e.g. Productus). Some, like Crania, are attached by the close adhesion of one valve to the rock ; others (e.g. Strophalosia) by spines given off from the surface of the shell. More commonly, however, the attachment takes place by means of a stalk or peduncle ; this is a cylindrical process, in some genera long, in others short, connected with the mantle, and passing out either through an opening in the ventral valve (fig. 72 A,/) or between the umbones (e.g. Lingida, fig. 76). It is composed mainly of supporting- tissue with a sheath of horny material, but in some forms there are muscular layers also. In Lingida, which com- 11—2 164 BRACHIOPODA monly lives in burrows in the sand of the sea-floor, the contraction of the muscles of the peduncle serves to with- draw the animal from the surface into its burrow. The opening for the passage of the peduncle varies considerably in different genera, and is a feature of importance in classification. The simplest case is that found in Lingula and some others, in which the opening is shared by both valves. In other types we find that the peduncle-opening is confined to the ventral valve ; in Distinct the opening is completely enclosed by the shell and is often near the centre of the valve, consequently the peduncle comes out at right angles to the plane of the valves. Sometimes, as in Orthis (fig. 80), the peduncle- opening is in the form of a triangular fissure, under the umbo, known as the delthyrium. In brachiopods belong- ing to the group Telotremata, a delthyrium is found in young individuals, but subsequently becomes partly closed by two plates, which grow inwards from the sides of the delthyrium and sometimes meet in the middle line. These two plates form the deltidium (fig. 72 A, d). In Rhyn- chonella the two plates usually meet, but a small circular or ovate opening (the foramen) is left near the centre for the peduncle. In Magellania (fig. 72 A, f) the foramen is quite at the apex of the umbo, its lower boundary being formed by the deltidium (d). In genera belonging to the Protremata and a few of the Neotremata, the delthyrium is more or less completely closed by a single plate known as the pseudo-deltidium ; this at first sight closely resembles the deltidium, but is really of a different nature. It originates on the dorsal surface of the body, but subse- quently becomes attached to the ventral valve, and then continues to grow by secretion from the peduncle. The deltidium, on the other hand, is formed by the edge of the BRACHIOPODA 165 ventral lobe of the mantle and consists of a pair of plates which, in some cases, coalesce. The pseudo-deltidium is developed at an earlier stage in the life of the in- dividual than the deltidium, and grows from the apex of the delthyrium downwards, becoming fused to the ventral valve. The two valves of the brachiopod can be opened and closed by means of muscles (fig. 69); those which open them are called the divaricators (c, c), those which close them, the adductors (a). When the soft parts of the animal have Fig. 72. Magellania [ = Waldheimia]flavescens, Recent. A, Interior of ventral valve. /, foramen ; d, deltidium ; t, teeth ; a, impressions of adductor muscles ; c, c', impressions of divaricator muscles ; b, b", muscles of the peduncle. B, Interior of dorsal valve. c, c', cardinal process ; b", hinge-plate ; s, dental sockets ; I, loop ; a, a', adductor impressions; c, point of attachment of the smaller divaricator. (After Davidson.) x 1^. been removed the places where the muscles were attached to the interior of the shell are indicated by a difference in the surface such as striation, or by slight depressions or elevations ; these markings are termed the muscular impressions. In the articulate brachiopods there are 166 BRACHIOPODA generally five or six pairs of muscles. In the genus Magellania there are two pairs of divaricators (fig. 69 c, c) and one of adductors (a). Both pairs of the former are attached to a process (the cardinal process, fig. 72 B, c, c') on the dorsal valve between the teeth sockets, and one pair join the ventral valve near its centre (fig. 72 A, c), while the other pair, which are smaller, are attached nearer the posterior border ( in the Dimyaria there are two in each valve, one being near the anterior border, the other near the posterior; in the Monomyaria the single adductor impression is usually near the middle of the valve. When, as in the genus My a, the two muscles are placed at equal distances from the hinge-margin, they are of nearly the same size, since on account of their position they are equally efficient in closing the valves; but in forms like Mytilus, where the shell is very inequilateral and the anterior muscle is close to the umbo but the posterior at a considerable distance from it, the latter is much larger than the former, since it is placed in a more advantageous position for closing the valves. For the same reason the single muscle of the Monomyaria is attached near the centre of the valves. Less important than the adductor impressions are those produced by the muscles for the MOLLUSCA. LAMELLIBRANCHIA 203 movement of the foot (protractors and retractors) ; these occur close to the anterior and posterior adductors. Passing from one adductor impression to the other in each valve is a linear depression, caused by the attach- ment of the muscles of the mantle to the shell, and known as the pallial line (pi). In some forms this line runs evenly between the two adductor impressions and parallel with the margin of the valve ; it is then said to be simple or entire. But in those genera which possess retractile siphons the pallial line bends inward just before reaching the posterior adductor ; this indentation is known as the pallial sinus (s), and is caused by a part of the pallial muscles which serve for the retraction of the siphons. The hinge is formed by projections known as teeth, which alternate in the two valves, the teeth of one valve fitting into the depressions between those of the other. The margin of the valve on which the teeth occur is known as the hinge-line; generally it is curved, but in some genera it is straight (e.g. Area). Several types of hinge may be recognised: — (1) Taxodont : the teeth are numerous and more or less similar in form and size, e.g. Nucula (fig. 93 A). (2) Dysodont : the teeth are of a simple type, and are developed from internal ribs at the margin of the valve ; the hinge-margin may be simple or somewhat thickened, e.g. Mytilus. (3) Isodont : there are two strong teeth of equal size in each valve, which fit into corresponding sockets in the other valve ; between the teeth is a median ligament-pit, e.g. Spondylus (fig. 93 D, E). (4) Schizodont : the teeth are few in number, thick, and sometimes grooved ; the middle tooth in the left valve is often bifid, e.g. Trigonia (fig. 93 B, C). (5) Heterodont : the teeth are few in number and not all of uniform shape and size ; some (usually two or three) are placed immediately 204 MOLLUSCA. LAMELLIBRANCHIA under the umbo and are known as the cardinal teeth, others, termed laterals, are placed in front of and behind the umbo, forming the anterior and posterior laterals ; some or all of the cardinals or of the laterals may be -c'^'WBj Fig. 93. Some types of hinge. A, Nucula. a, anterior adductor ; b, posterior adductor ; I, ligament-pit. B, C, Trigonia. B, right valve with two large striated teeth ; C, left valve with three teeth. D, E, Spondylus ; D, right valve ; E, left valve ; a, b, teeth ; c, d, sockets into which the teeth fit; e, area; I, ligament-pit. F, Lucina (right valve) ; a, anterior lateral tooth ; b, cardinal tooth ; c, pos- terior lateral tooth ; /, ligament. G, Lutraria (left valve) ; a, strong A-shaped cardinal tooth; /, process to which the ligament is attached. All drawn from recent specimens. absent; the hinge-margin is usually extended as a vertical lamina or hinge-plate (fig. 93 F) on which the teeth are borne, e.g. Meretrix. (6) Desmodont : true teeth and a MOLLUSCA. LAMELLIBRANCHIA 205 hinge-plate are absent, but one or more laminae or ridges are developed at the hinge-margin, e.g. Pleuromya. (7) In some genera teeth are absent ; this may be a primitive character, as in Grammysia, or the result of degeneration as in Ostrea and Anodonta. In some genera (e.g. Area) there is, between the hinge- line and the umbo of each valve, a flattened triangular part of the shell, known as the area (fig. 93 D, e) ; when this is present the umbones of the two valves are of course widely separated. The lunule and escutcheon (p. 202) appear to represent the anterior and posterior parts of the area. Some lamellibranchs (e.g. Pecten) have, on each side of the umbo, triangular or wing-like extensions of the shell, known as ears. In the brachiopods the valves are opened by di- varicator muscles, but in the lamellibranchs the work of these muscles is performed by the ligament. This con- sists of two parts, the external (fig. 92, I), and the internal (sometimes erroneously termed the cartilage) (fig. 93 G, I). One or other may be absent. The external ligament is composed of horny material ; it is placed at the hinge- margin, usually posterior to the umbones, and is frequently attached to more or less prominent ridges; in some genera (Pectunculus) the external ligament extends both in front of and behind the umbones. The internal ligament consists of parallel elastic fibres, and is placed in grooves or sockets along the hinge, so that when the valves are closed it is compressed, and, being elastic, tends to force the valves apart — its action is similar to that of a piece of indiarubber placed in the hinge-line of a door. The external ligament acts like a C-spring, and is bent when the valves are closed. Consequently, in order to open the shell, the animal has merely to relax its adductor 206 MOLLUSCA. LAMELLIBRANCHIA muscles. Occasionally the ligament is preserved in fossil specimens. The length of a lamellibranch shell is measured from the anterior to the posterior margin (fig. 92 B, a — p), the breadth or height from the umbo to the ventral margin (d — v) the thickness from one valve to the other at right angles to the lines of length and breadth. Fig. 94. Vertical section of the shell of a recent Unio, cut in a radial direction from the umbo ; the right-hand side of the section is near the ventral margin, a, pearly or nacreous layer, in which the later lamella overlap the earlier and extend on to (b) the prismatic layer ; c, periostracum. x 10. The shell is secreted by the mantle ; its structure varies in different groups. In some genera it consists of two calcareous layers ; the inner is the pearly or nacreous layer, and is formed of numerous thin lamellae (fig. 94 a) ; the outer is the prismatic layer (figs. 94 b, 95), and is com- posed of prisms placed more or less nearly perpendicular to the surface of the shell, each prism being encased in a MOLLUSCA. LAMELLIBRANCHIA 207 Fig. 95. Section of pris- matic layer of recent Pinna, parallel to the surface of the shell and at right angles to the prisms. Magnified. thin membranous sheath, which can be isolated by dis- solving the calcareous part of the shell in acid. The external sur- face is covered by a green or brownish horny layer (c), the peri- ostracum (frequently referred to as the ' epidermis '). The prismatic layer is formed by the margin of the mantle only; the pearly layer by the general surface of the mantle, and this layer grad- ually encroaches on the former, which consequently cannot after- wards increase in thickness, whereas the pearly layer may do so throughout the life of the animal. The pearly layer is absent in many forms, and the prismatic structure of the outer layer may be indistinct or altogether wanting, and this layer has then a porcellanous appearance. Sometimes the shell consists entirely of aragonite or of calcite ; in other cases one layer may be of calcite and the other of aragonite. The surface of the shell may be smooth, or may be ornamented with radiating or concentric ribs and striae, or with tubercles, or spines. Often the exterior shows con- centric lamellae, which represent periods of growth. The part of the shell at the umbo is that which was first formed, and often differs in ornamentation and form from the other parts. The margins of the valves may be smooth or crenulated ; sometimes, as in some species of Pecten, the entire shell is corrugated, thus increasing its strength without materially adding to the weight. In many genera the two valves can be completely closed, in 208 MOLLUSCA. LAMELLIBRANCHIA others they are always open at some part, and are then said to be gaping ; this gape occurs most frequently at the posterior end, but sometimes also anteriorly. Sometimes the small embryonic shell, known as the prodissoconch, is found at the umbo of the adult shell ; this represents the protegulum of the Brachiopods (p. 170) and the proto- conch of the Gasteropods and Cephalopods. In order to be able to distinguish the right and left valves we must determine first the anterior and posterior margins. When the soft parts of the animal are present this is easily done ; but when the shell only is before the observer the points to be noticed are the following : — (1) The umbones are generally directed anteriorly ; and in inequilateral shells, the posterior part of the valves is, with only a few exceptions (Nucula, Lima), longer than the anterior part. (2) The lunule is anterior to the umbones. (3) The external ligament is commonly posterior to the umbones, and is never entirely in front of them. (4) The pallial sinus is posterior. (5) When one adductor impression only is present, it is the posterior. (6) When one adductor impression is distinctly larger than the other, the larger is the posterior. Having found the anterior and posterior margins, the shell should be placed with the dorsal surface uppermost and the anterior margin pointing away from the observer, then the right and left valves will be on his right- and left- hand sides respectively. MOLLUSCA. LAMELLIBRANCHIA 209 Most of the lamellibranchs are free, but a few forms, such as the oyster, are permanently attached by one valve, which adheres firmly to a rock or some other object. In some cases the right valve is fixed, in others the left. The shell in these forms becomes irregular and the fixed valve is larger and thicker than the free valve. Other genera are attached by means of a byssus (p. 199), which often passes out through a notch or sinus in the margin of one or both valves. In the free forms, movement takes place usually by means of the foot, but some genera (Pecten, Lima) move by the rapid opening and shutting of the valves. A few are capable of making borings into various substances ; thus Teredo, the ship-worm, bores into wood, Lithodomus and Saocicava into limestone, and Pholas into various materials, such as sandstone, limestone, gneiss, peat, and amber. Wood perforated by Teredo has been found fossil in various formations of Eocene and Oligocene age. The features which more especially characterise the lamellibranchs as a class are : the absence of a head and of organs of mastication, the bilateral symmetry, the division of the mantle into two lobes, the bivalve shell and the lamellar gills. Although at first sight the shell appears to resemble closely that of the brachiopods, it differs in several important respects : — (1) the valves are right and left, instead of dorsal and ventral, (2) they are generally inequilateral and equivalve, (3) teeth occur on both valves, (4) a ligament is present, (5) the umbones are never perforated for a peduncle, (6) the microscopic structure of the shell is different. Various classifications of the Lamellibranchia have been, from time to time, proposed. By Lamarck this class was divided into the Monomyaria and the Dhnyaria, depending w. p. 14 210 MOLLUSCA. LAMELLIBRANCHIA on the presence of one or two adductor muscles. Between these two groups, however, there are numerous inter- mediate forms in which the anterior muscle is smaller than the posterior ; and, further, one genus (Dimya), which in other respect agrees with some of the Mono- myaria, possesses two adductor muscles. A third division, the Heteromyaria, was established for the genera in which the anterior adductor is small, but its limits are not well defined, and moreover, in Mytilus it is found that whilst in M. edulis both muscles are present, in the closely allied species, M. latus, the anterior adductor is absent. Another classification, which was suggested by Fleming, was based on the presence or absence of siphons ; the two groups being termed the Siphonida and the Asiphonida; the former has been further divided according as to whether the pallial line is entire (Integripalliata) or provided with a sinus (Sinupalliata). Neumayr, Dall, and others have divided the lamellibranchs into groups based largely on the character of the hinge (p. 203) ; whilst the classifica- tion brought forward by Pelseneer, is founded on the form and structure of the gills. The divisions which are pro- visionally used in the following pages are similar to those proposed by Neumayr. 1. Hinge taxodont. Two nearly equal adductor muscles. Siphons usually wanting. Nucula1 (fig. 93 A). Shell equivalve, trigonal or oval, closed, posterior side very short ; umbones directed posteriorly. Surface smooth or ornamented. Interior nacreous. Margins of valves smooth or crenulated. Hinge angular, with a median internal triangular ligament-pit, and numerous sharp teeth. Adductor im- pressions nearly equal. Pallial line simple. Silurian to present day. Ex. N. hammeri. Lias ; N. dixoni, Bracklesham Beds. 1 All the genera of Mollusca described are marine unless otherwise stated. MOLLUSCA. LAMELLIBRANCHIA 211 Nuculana ( = Leda). Similar to Nucula. Posteriorly the shell is produced and pointed, and provided with a ridge or carina. Pallial line with a small sinus. Margins smooth. Lunule lanceolate. Silurian to present day. Ex. N. lachryma, Inferior Oolite to Corn- brash ; N. caudata, Pliocene to present day. Ctenodonta. Shell oval or elongated, nearly equilateral, smooth or with concentric striee. Ligament external. No area. Hinge curved or angular, with numerous small teeth. No internal ligament-pit. Pallial line simple. Cambrian to Carboniferous. Ex. C. pectunculoides, Ordovician. Area. Shell thick, generally equivalve, sub-quadrangular, ventricose, ornamented with radiating ribs and concentric strise ; margins smooth or dentate ; closed or gaping ventrally. Hinge straight, with numerous, small, equal, transverse teeth. Umbones prominent, separated by the large areas, which have numerous ligamental grooves converging from the hinge-margins to the um- bones. Adductor impressions sub-equal, the anterior rounded, the posterior divided. Pallial line simple. Jurassic to present day. Ex. A. tetragona, Pliocene to present day ; A. granosa, Eecent. Cucullaea. Shell similar to Area. Hinge with short central transverse teeth, and two to five lateral teeth nearly parallel to the hinge-margin. Posterior adductor fixed to a thin raised plate. Jurassic to present day. Ex. C. fibrosa, Upper Greensand. Pectunculus ( = Glycimeris, Axincea). Shell thick, solid, sub- orbicular, equivalve, almost equilateral. Surface smooth or radially striated. Ligament external. Umbones central, slightly curved posteriorly, separated by a small triangular area provided with diverging grooves for the ligament. Hinge arched or semicircular, with a row of numerous, small, strong, transverse teeth, obliterated at the centre in the older forms by the growth of the area. Margins crenulate inside ; adductor impressions sub-equal — the anterior sub- triangular, the posterior oval or rounded. Pallial line with a very small sinus. Cretaceous to present day. Ex. P. glycimeris, Pliocene to present day. 2. Hinge dysodont, but teeth sometimes rudimentary or absent. Anterior adductor smaller than the posterior, sometimes absent in the adult. Pallial line simple. 14—2 212 MOLLUSCA. LAMELLIBRANCHIA Mytilus. Shell thin, equivalve, very inequilateral, elongated, sub-triangular, posterior border rounded. Umbones sharp, terminal, anterior. Teeth small or absent. Ligament linear, marginal, sub-internal. Anterior adductor impression small, placed near the umbo ; posterior large ; pallial line simple. Trias to present day. Ex. M. edulis, Pliocene to present day. Modiola. Shell similar to Mytilus, but oblong, inflated in front. Umbones obtuse, anterior, but not terminal. Devonian to present day. Ex. M. modiola, Recent ; M. imbricata, Inferior Oolite. Lithodomus ( = Lithophagus). Shell similar to Modiola; sub-cylindrical, rounded in front, wedge-like behind. Lithodomus bores into limestone, etc. Carboniferous to present day. Ex. L. inclusus, Inferior Oolite to Corallian. Modiolopsis. Shell thin, smooth, elongate, very inequilateral, anterior part small, posterior part enlarged. Umbones nearly terminal, close together ; a depression crosses the valves obliquely from the umbo. No teeth. Anterior adductor impression deep ; posterior adductor large, faintly marked. Ordovician and Silurian. Ex. M. modiolaris, Ordovician. Myoconcha. Similar to Modiolopsis, but usually with a long cardinal and a long slender posterior lateral tooth in the right valve. Carboniferous to Chalk. Ex. M. crassa, Inferior Oolite ; M. cretacea, Chalk. Hippopodium. Shell very thick, very convex, oblong ; surface with lines of growth. Umbones large, anterior. Hinge thick, with one oblique tooth which may disappear in old specimens. Adductor impressions deep. Pallial line simple. Lias to Great Oolite. Ex. H. ponderosum, Lower and Middle Lias. Myalina. Shell thick, trigonal, oblique, very inequilateral, with pointed umbones at the anterior extremity. Anterior marginal part of valves sharply bent. Posterior part compressed, wing-like. Hinge-line straight, long. Hinge-margin broad with longitudinal striations. Anterior adductor near the ventral edge of the anterior end of the hinge-plate. Posterior adductor large, oval. Pallial line simple. Surface with growth-lines, often lamellar. Silurian to Permian ; common in Carboniferous. Ex. M. verneuili, Carboni- ferous. MOLLUSCA. LAMELLIBRANCHIA 213 Pinna. Shell generally thin, with coarse prismatic structure (fig. 95), equivalve, inequilateral, wedge-shaped, without ears. Umbones sharp, anterior, terminal. Valves truncate and gaping posteriorly. Hinge-line straight, long. No teeth. Ligament linear, almost entirely internal, lodged in a groove. Posterior adductor large, sub-central ; anterior adductor close to the umbo. Devonian to present day. Ex. P. hartmanni, Lias ; P. ajfinis, London Clay. Gervillia. Shell obliquely elongated, very inequilateral, slightly inequivalve, the left valve a little more convex than the right ; umbones almost terminal. Hinge straight, with broad margin on which are numerous perpendicular, widely-separated ligament-pits ; with two or more oblique ridge-like teeth. Ears indistinctly limited from the rest of the shell, the anterior very short, the posterior long. Posterior adductor imj>ression large, sub- central. Trias to Eocene. Ex. G. subla?iceolata, Lower Greensand. Inoceramus. Shell variable in form, circular, oval, or oblong ; inequilateral, inequivalve, ventricose or compressed, with ears indis- tinctly limited. Umbones prominent, rather anterior. No teeth. Surface with concentric (or rarely radiating) furrows. Hinge-line straight, usually long, with numerous parallel, close-set, transverse ligament-pits. Adductor impression rarely visible. Inner layer of shell thin and nacreous ; outer layer thick, formed of large prisms. Lias to Chalk ; common in Upper Cretaceous. Ex. /. concentricus, Gault ; /. brongniarti, Chalk. Perna. Shell nearly equivalve, inequilateral, compressed, sub- quadrate or sub-circular. Umbones at the anterior end. Hinge- line straight, without teeth ; hinge-margin broad, with numerous transverse, elongated ligament-pits placed close together and parallel with one another. Right valve with a byssal sinus. Adductor im- pression large, sub-central, double ; pallial line simple. Posterior ear often large, not distinctly limited. Trias to present day. Ex. P. mytiloides, Upper Jurassic ; P. epkippuim, Recent. Pteria ( = Avicula). Shell oblique, inequilateral, inequivalve, left valve more convex than the right. Interior nacreous. Hinge long, straight, with one or two small cardinal teeth and a lamellar lateral tooth. Posterior ear wing-like and longer than the anterior. A byssal sinus under the right anterior ear. Area small. Ligament long, partly internal, partly external, in a groove. Posterior 214 MOLLUSCA. LAMELLIBRANCHIA adductor impression large, sub-central. Silurian to present day. Ex. P. media, Barton Beds ; P. Mrundo, Recent. Sub-genera, or closely allied genera, are Actinopteria, Leiopteria, Ptero?iites, Oxytoma. Pseudomonotis. Similar to Pteria, but the shell is oval, the left valve large and very convex, and the right valve flattened ; the anterior ear small or rudimentary. Devonian to Cretaceous. Ex. P. ecMnata, Cornbrash. Aucella. Shell thin, obliquely elongate, inequilateral, inequi- valve, with concentric folds or ribs. Left valve convex, with prominent incurved umbo ; ears indistinctly limited. Right valve flattened, anterior ear triangular, with a deep byssal sinus ; posterior ear indistinctly limited. Hinge-line straight, short, without teeth. Ligament external. Upper Jurassic and Lower Cretaceous. Ex. A. keyserlingi, Speeton Series. Pterinea. Form similar to Pteria ; left valve flattened. Hinge with small transverse anterior teeth, and laminar posterior teeth. Area large, with longitudinal grooves for the ligament. Posterior adductor impression large, shallow ; anterior impression small, deep, below the anterior ear. Silurian to Carboniferous ; common in Devonian. Ex. P. Icevis, Devonian. Posidonomya. Shell thin, oblique, oval, equivalve, com- pressed, with concentric furrows. Umbones small, sub-central. Hinge-line straight, short, without teeth ; posterior ear compressed, indistinctly limited. Silurian to Jurassic. Ex. P. becheri, Carboni- ferous. Conocardium. Shell more or less trigonal, very inequi- lateral, with radiating ribs ; posterior side short, truncated, forming a cordate posterior end, produced into a long tube ; anterior side oblique, compressed, wing-like, gaping. Umbones small, pointed, incurved. Hinge-line long, straight. Ligament partly external, partly internal, attached to a plate behind the umbones. Anterior adductor impression large, deep ; posterior impression shallow. Inner margins of valves toothed. The truncated end bearing the tube is regarded by some authors as anterior, and the wing-like end as posterior. The affinities of this genus have not yet been deter- mined. Silurian to Carboniferous. Ex. C. Mbernicum, Carboniferous Limestone. MOLLUSCA. LAMELLIBRANCHIA 215 3. Hinge, when well-developed, isodont ; teeth some- times absent or imperfect. A median pit for the ligament. Siphons absent. Posterior adductor only present. Spondylus (fig. 93 D, E). Shell irregular, with ears, attached by the right valve ; surface with radiating ribs which are spiny or foliaceous. Eight valve larger and more convex than the left, with a triangular area. Two strong teeth in each valve, which fit into corresponding sockets in the other valve ; between the teeth a triangular ligament-pit ; ligament partly external. Adductor im- pression large, sub-central. Jurassic to present day. Ex. S. spino- sus, Chalk ; S. rarispina, Bracklesham ; S. gcederopus, Recent. Plicatula. Similar to Spondylus. Surface smooth, folded or scaly. Without ears. Area very small. Ligament internal. Adductor impression excentric. Trias to present day. Ex. P. spinosa, Lias ; P. inflata, Chalk ; P. cristata, Recent. Anomia. Shell thin, irregular or sub-circular, attached by a calcified byssus, which passes through a rounded sinus near the umbo of the right valve. Right valve flattened, with a central adductor impression; left valve larger, convex, with three impres- sions of the byssal muscles and one of the adductor. Teeth absent. Lias to present day. Ex. A. ephippium, Pliocene to present day. Pecten. Shell sub-circular, ovate or trigonal, closed, almost equilateral, inequivalve or nearly equivalve. Surface frequently with radiating ribs or striae, sometimes smooth or with concentric ridges. Hinge-line straight ; with well-developed ears, with or without a byssal sinus. A central, triangular pit for the internal ligament. Adductor impression large, a little excentric. Carboni- ferous to present day. Pecten includes a very large number of species, which are grouped into sub-genera and sections, of which the more important are : — JEquipecten (ex. Pecten asper, Upper Greensand, P. opercularis, Pliocene) ; Amusium (ex. P. pleuronectes, Recent) ; Camptonectes (ex. P. lens, Jurassic) ; Chlamys, Hinnites, Xeithea (see below) ; Syncyclonema (ex. P. orbicularis, Chalk). Chlamys : shell ovate or trigonal, nearly equivalve, surface with radial ribs. Ears large — the anterior larger than the posterior and with a deep sinus for the byssus on the right valve. Trias to present day. Ex. P. islandicus, Pleistocene and Recent. 216 MOLLUSCA. LAMELLIBRANCHIA Hinnites : the young shell is like Chlamys ; the adult is irregular like Ostrea, and is attached by the right valve. Cretaceous to present day. Ex. H. cortesi, Pliocene. Pecten (restricted) : right valve very convex, left flattened. Ears nearly equal. No byssal sinus. Cretaceous to present day. Ex. P. maximus, Pliocene to present day. Neithea : similar to the last ; with numerous small denticles on the hinge. Cretaceous. Ex. P. {Neithea) quadricostatus, Upper Greensand. Lima. Shell obliquely oval, anterior part larger than the posterior part, equivalve, compressed, with radiating striae or ribs. Valves gaping anteriorly and sometimes posteriorly. Umbones distant, sharp. Hinge-line straight without teeth, with unequal ears. On each valve a triangular area, with a central ligament- pit. Adductor impression large. Two small pedal impressions. Carboniferous to present day. Ex. L. gigantea, Lias ; L. cardii- fonnis, Middle Jurassic ; L. squamosa, Kecent. Sub-genera Plagi- ostoma, Limatula, Mantettum, etc. Aviculopecten. Shell ovate, slightly inequilateral ; right valve less convex than the left. Umbones distinct ; hinge-line straight, long ; ears distinctly limited, the posterior larger than the anterior and often wing-like ; a byssal sinus beneath the anterior ear in the right valve. Hinge-margin with narrow, nearly parallel grooves. A central pit for the internal ligament. Adductor im- pression large, sub-central. Surface usually with radial ribs, and concentric lines, the ornamentation different on the two valves. Devonian to Permian. Ex. A. tabidatus, Carboniferous. Pterinopecten. Similar to Aviculopecten ; posterior ear not distinctly limited ; both valves with the same kind of ornamentation. Devonian and Carboniferous. Ex. P. papyraceus, Carboniferous. Ostrea. Shell with lamellar structure, irregular, inequi valve, slightly inequilateral, fixed by the left (larger) valve. Left valve convex, often with radiating ribs or stria? ; umbo prominent, some- times directed anteriorly, sometimes posteriorly. Eight valve flat or concave, often smooth. Ligamental cavity triangular or elon- gated. Hinge without teeth. Adductor impression sub-central ; pallial line indistinct. Trias to present day. Ex. 0. deltoidea, Kimeridgian ; 0. edulis, Pliocene and Recent. MOLLUSCA. LAMELLIBRANCHIA 217 Alectryonia. Similar to Ostrea. Both valves with coarse angular folds ; edges of valves toothed. Trias to present day. Ex. A. gregaria, Corallian ; A. frons, Lower Chalk. Grryphaea. Shell similar to Ostrea, but free in the adult stage ; left valve large and convex, with a prominent incurved umbo. Right valve flattened or concave. Lias to present day. Ex. G. arcuata { = incurva\ Lias. Exogyra. Similar to Ostrea. Shell fixed by the left (larger) valve. Right valve flat, resembling an operculum. Umboues more or less spiral, directed posteriorly. Upper Jurassic to Chalk. Ex. E. cohcmba, Upper Greensand. 4. Hinge schizodont, or formed of thick, irregular teeth. Valves equal. Two nearly equal adductors. Ligament usually external and behind the umbones. Pallial line simple. Inner layer of shell usually pearly. Trigonia (fig. 93 B, C). Shell thick, ornamented with rows of tubercles or with concentric (sometimes radiating) ribs ; trigonal, very inequilateral, anterior margin rounded, posterior produced and angular. Generally with a ridge extending from the umbones to the posterior border, cutting off a portion which has a different orna- mentation. Umbones anterior, directed posteriorly. Cardinal teeth diverging, grooved, two in the right valve, three in the left, the central tooth in the latter being bifid. Ligament marginal, thick. Adductor impressions deep, the anterior smaller than the poste- rior, and placed near the umbones. A pedal impression in front of the posterior adductor of each valve and also one in the umbo of the left valve. Pallial line simple. Interior of shell nacreous. Lias to present day. Ex. T. costata, Inferior Oolite to Cornbrash ; T. cla- vellata, Corallian. Schizodus. Similar in form to Trigonia ; shell thin and smooth, umbones placed anteriorly. Three teeth in each valve, the middle one being a cardinal ; the anterior lateral inconspicuous in the right valve. Adductor impressions shallow. Carboniferous and Permian. Ex. S. obscurus, Permian. Myophoria. Allied to Schizodus. Shell oval, triangular, or trapezoidal. Umbones anterior, often with a ridge extending to the 218 MOLLUSCA. LAMELLIBRANCHIA lower part of the posterior border. Surface nearly smooth or with radial ribs. Right valve with one, sometimes two, cardinal teeth, and ridge-like posterior lateral tooth. Left valve with a triangular, some- times bifid cardinal, and one anterior and one posterior lateral tooth. Adductor impressions with a ridge passing to the hinge. Trias and Rhsetic. Ex. M. laevigata, Trias. Unio. Shell thick, oval or elongated, with a thin periostracum. Surface smooth, tuberculate, striated, or folded ; interior nacreous. Umbones more or less anterior, often corroded. Ligament external, elongated. In the right valve one or two thick, irregular teeth below the umbo and a long lamellar posterior lateral tooth ; in the left valve, two thick irregular teeth near the umbo, and two long lamellar posterior lateral teeth. Adductor impressions very deep, especially the anterior. Pallial line simple. Inferior Oolite to present day. Lives in fresh water. Ex. U. littoralis, Pleistocene and Recent. Anodonta. Allied to Unio ; shell relatively thin, without teeth. Fresh water. Miocene (perhaps Purbeck) to present day. Carbonicola (= Anthracosia). Similar in form to Unio, but the anterior part of shell is broad and tumid, the posterior part narrow and compressed ; usually a constriction at the ventral border. Hinge-plate triangular, with or without cardinal teeth, no laterals. Adductors large, the anterior near the margin. Pedal impression above the anterior adductor. Carboniferous and Permian. Probably fresh water. Ex. C. robusta, Coal Measures. "j Anthracomya. Differs from Carbonicola chiefly in having the posterior part of the shell broad and expanded. Hinge-plate small, with a cardinal and one posterior lateral tooth. Carboniferous. Probably fresh water. Ex. A. adamsi. Cardinia. Shell trigonal, oval, or oblong, very inequilateral, compressed, thick, marked by lines of growth. Interior not na- creous. Umbones small, sharp, close together. Ligament external. Cardinal teeth small or obsolete ; in the right valve one anterior lateral tooth, in the left, one posterior lateral. Impression of anterior adductor very deep. Pallial line simple. Trias to Middle Jurassic (chiefly Lias). Ex. C. listeri, Lias. MOLLUSCA. LAMELUBRANCHIA 219 Megalodon. Shell thick, equi valve, smooth or with con- centric lines, convex, inequilateral, oval or rounded triangular. Umbones prominent, curved forward. Ligament external, long. Hinge-plate very large and thick ; teeth thick ; in the right valve two cardinals separated by a pit ; in the left valve one cardinal under the umbo and a small anterior cardinal ; no laterals. Anterior adductor impression small, semilunar ; posterior adductor long, shallow, on a ridge extending from the hinge to the posterior border. Devonian to Jurassic. Ex. M. cucullatus, Devonian. Pachyrisma (Trias and Jurassic) is allied to Megalodon. 5. Hinge heterodont ; hinge-plate usually well-de- veloped. Two nearly equal adductors. Ligament behind the umbones. Siphons usually well-developed. Shell without a pearly layer. (a) Pallial line usually simple. Cyprina. Shell orbicular or oval, convex, with concentric striae and a thick periostracum. Umbones prominent, incurved. Ligament external, prominent. Lunule seldom present. Right valve with a small anterior cardinal below a triangular median cardinal, an oblique bifid posterior cardinal, and a posterior lateral. Left valve with a small anterior cardinal, a vertical median cardinal, and a long oblique posterior cardinal. Adductor impressions oval. Pallial line entire. Margins of valves smooth. Lias to present day. Ex. C. islandica, Coralline Crag to present day. Isocardia. Similar to Cyprina. Umbones inflated, curved anteriorly or spirally inrolled. In each valve two nearly parallel cardinal teeth and one posterior lateral. Jurassic to present day. Ex. /. cor, Coralline Crag to present day. Astarte. Shell thick, inequilateral, more or less trigonal or sub-orbicular, compressed, closed. Surface usually with concentric furrows or striae. A thick periostracum is present. Umbones prominent. Lunule distinct. Escutcheon elongated. Ligament external. Two cardinal teeth in each valve, lateral teeth rudi- mentary. Adductor impressions strongly marked ; above the anterior one is a pedal impression. Pallial line simple. Trias to present day. Ex. A. omalii, Coralline Crag. 220 MOLLUSCA. LAMELLIBRANCHIA Opis. Shell trigonal, cordiform, convex, with an oblique keel ex- tending from the umbo to the posterior border. Umbones prominent, incurved or sub-spiral. Lunule large and very deep. Surface gene- rally with concentric furrows. One cardinal tooth in the right valve, two in the left. Pallial line simple. Trias to Chalk. Ex. 0. lunu- latus, Inferior Oolite. Crassatellites ( = Crassatella). Shell solid, oblong or sub- trigonal, attenuated behind. Surface smooth or concentrically furrowed. Margins of valves smooth or crenulated. Umbones small, close together. Lunule distinct. Ligament internal, placed in a pit under the umbo. Hinge with two (sometimes three) cardinal teeth, and some small laterals. Adductor impressions deep. Pallial line simple. Cretaceous to present day. Ex. C. sulcatus, Barton Beds. Cyrena. Shell cordiform, oval, or trigonal, usually with con- centric ridges ; umbones often corroded. Hinge with three cardinal teeth ; one anterior and one posterior lateral in the left valve, and two of each in the right valve. Ligament prominent, external. Pallial line usually entire. Lias to present day. Lives in fresh and brackish water. Ex. C. ceylanica, Recent. Corbicula. Similar to Cyrena, but with the lateral teeth lamellar and transversely striated. Eocene to present day. Fresh water. Ex. C. Jlumi?ialis, Pliocene to present day. Cardita. Shell oval or oblong, elongated, very inequilateral, with prominent scaly ribs ; often a little gaping and sinuous at its ventral margin. Umbones prominent, anterior. Lunule present. Ligament external. In the right valve two long, parallel cardinal teeth, and a small anterior lateral tooth. In the left valve one short anterior cardinal, and one long posterior cardinal, and a rudimentary posterior lateral tooth. Adductor impressions large. Pallial line simple. Trias to present day. Ex. C. calyculata, Recent. Venericardia. Shell oval, triangular, or heart-shaped, inequilateral, with radiating ribs. Umbones prominent. Ventral margin crenulated internally, not sinuous. Ligament external. Hinge-plate thick ; in the right valve two oblique cardinal teeth and one small or rudimentary anterior lateral; in the left two diverging MOLLUSCA. LAMELLIBRANCHIA 221 cardinal teeth. Adductor impressions unequal. Pallial line simple. Cretaceous to present day. Ex. V. planicosta, Bracklesham Beds. Chama. Shell irregular, thick, inequivalve, fixed by the umbo of the larger valve (generally the left, sometimes the right). Umbones spiral or sub-spiral, directed anteriorly, that of the fixed valve longer than the other. Surface with concentric lamellae or spines. The fixed valve larger and much deeper than the other. In each valve a strong cardinal tooth, and sometimes in the inferior valve a narrow curved posterior tooth also. Ligament external, in a deep groove, prolonged towards the umbones. Adductor impres- sions large, the anterior commencing near the hinge-line. Pallial line simple. Upper Cretaceous to present day. Ex. C. squamosa, Barton Beds. Diceras. Shell thick, inequivalve, fixed by umbo of larger valve. Umbones large, inrolled, directed forwards. Ligament external, in a curved groove at the posterior margin of the hinge. Hinge-plate very thick ; right valve with a large, elongate, curved posterior cardinal tooth parallel to the ligament groove, and an anterior pit ; left valve with a large ear-shaped cardinal tooth and a pit for the tooth of the right valve. Adductor impressions distinct, the posterior on a raised elongated plate. Pallial line simple. Upper Jurassic. Ex. D. arietinum. Requienia and Toucasia (Cretaceous) are related to Diceras. Hippurites (figs. 96, 97). Shell very large and massive, conical or sub-cylindrical, not spiral, very inequivalve, fixed by the apex of the larger valve. The large {lower) valve elongate-conical, striated or smooth, and with three parallel furrows extending from the apex to the cardinal margin, due to folds of the shell-wall which give rise to three corresponding ridges in the interior. Hinge consists of a small cardinal tooth and of cardinal pits ; anterior adductor impression large and divided into two separate parts ; posterior adductor in a depression. Small {upper) valve flattened or slightly convex, operculiform, porous, the pores leading into canals ; with a central umbo and two prominent teeth ; the anterior tooth very large with two surfaces at its base for the attachment of the adductors ; the posterior tooth smaller with a tooth-like process for the posterior 222 MOLLUSCA. LAMELLIBRANCHIA adductor. The small valve is formed of two layers ; the outer is thin and prismatic, the inner is porcellanous and traversed by numerous canals. The outer layer of the large valve is formed of small prisms arranged in parallel layers obliquely to the surface of the shell ; the inner is porcellanous and formed of thin leaflets. Upper Cretaceous. Ex. H. comu-vaccinum. Fig. 96. Fig. 97. Fig. 96. Transverse section of the large valve of Hippurites comu- vaccinum. r, umbonal cavity; e, internal layer of shell; d, external layer; I, m, n, folds; t, cardinal teeth; a, anterior adductor; a', posterior adductor ; c, cavity ; c', cardinal fossa. Cretaceous. (From Woodward.) x ^. Fig. 97. Longitudinal section of the small valve and part of the large valve of Hippurites comu-vaccinum. u, umbonal cavity of small valve; d, external layer of shell; r, internal layer; i, part of cavity between the valves; a, anterior adductor; a', posterior adductor; t, t' anterior and posterior cardinal teeth of small valve ; I, cardinal tooth of large valve. (From Woodward.) x |. Radiolites. Shell large, thick, valves very unequal. The large (loiver) valve conical or sub-cylindrical, generally straight, fixed by its apex (umbo) ; surface with vertical ribs, and thick, horizontal projecting layers which are more or less regularly folded ; with a ligamental fold extending from the apex to the margin, and two vertical undulations corresponding to the positions of the anal and branchial orifices ; outer layer of shell very thick, formed of polygonal or prismatic cells ; inner layer thin, porcellanous, often MOLLUSCA. LAMELLIBRANCHIA 223 not preserved ; an elongate median tooth ; two adductor im- pressions widely separated. The small (upper) valve generally convex or conical, sometimes flat, with central umbo ; two straight, elongate, grooved teeth ; the two adductor muscles were attached to plates on either side of the teeth ; shell structure similar to that of the larger valve, but with the external layer thinner. Upper Cretaceous. Ex. R. angeiodes. Unicardium. Shell oval or rounded, inflated ; surface with concentric lines or ridges. Umbones prominent, curved inwards. In each valve a small cardinal tooth which is often obsolete, and a posterior ridge separated from the margin by a furrow in which is the external ligament. Adductor impressions elliptical. Trias to Cretaceous. Ex. U. cardioides, Lias. Lucina (fig. 93 F). Shell orbicular or oval, slightly inequi- lateral, usually ornamented with concentric lines or ridges. Lunule usually distinct. An oblique furrow extends from the umbo to the posterior border. Hinge usually with two cardinal and one or two lateral teeth in each valve ; the lateral, or the cardinal, may be absent. Ligament elongated, external, sometimes partly internal. Adductor impressions well marked, the anterior elongated and placed mainly within the pallial line, the posterior oval. Pallial line entire. Margins of valves smooth or finely crenulated. Trias to present day. Ex. L. borealis, Coralline Crag to present day. Cardium. Shell convex, slightly inequilateral, cordate or oval, generally closed. Umbones prominent, incurved, turned slightly to the anterior end. Surface with radiating ribs, which are often spiny. Margins of valves crenulated. Right valve with one or two cardinal teeth, two anterior laterals, and one or two posterior laterals; left valve with two cardinals, one anterior lateral and one posterior lateral. Ligament external. Adductor impressions shallow. Pallial line entire. Trias to present day. Ex. C. acu- leatum, Pleistocene and Recent ; C. edule, Pliocene to present day. Protocardia. Similar to Cardium^ but with radiating ribs on the posterior part of the shell only, the remainder with concentric ribs. Jurassic to present day. Ex. P. hillana, Upper Greensand. 224 MOLLUSCA. LAMELLIBRANCHIA Thetironia ( = Thetis). Shell thin, oval, rounded, very convex, slightly or moderately inequilateral. Umbones prominent, curved inward and slightly forward. No lunule. Ligament external. Two small conical or tubercular cardinal teeth under the umbo in each valve ; no laterals. Adductor impressions near the anterior and posterior margins. Pallial line simple. Two internal ribs meet at an acute angle near the umbo and extend ventrally to the level of the adductors. Surface of shell nearly smooth, with concentric lines and radial rows of small pits which are more distinct on the posterior part than elsewhere. Cretaceous. Ex. T. minor, Lower Greensand. (b) Pallial line usually with a sinus, but sometimes sinuous only. Venus. Shell thick, oval, convex, ornamented with concentric lamellsG, sometimes with radial ribs ; lunule distinct. Margins of valves finely crenulate. Hinge-plate wide ; in each valve three cardinal teeth, often bifid, no lateral teeth. Ligament external, prominent. Pallial sinus short, angular. Miocene to present day. Ex. V. casina, Pliocene to present day ; V. verrucosa, Eecent. Meretrix (fig. 92). Shell thick, ovate, sub-trigonal, convex, smooth or with concentric ornament. Margins of valves smooth. Lunule present. Ligament external. Hinge-plate thick, with three cardinal teeth in each valve, two anterior laterals in the right, and one in the left valve. Pallial sinus angular or rounded. Cretaceous to present day. M. meretrix, Recent ; Ex. M. {Callista) planus, Upper Greensand ; M. {Callista) chione, Recent. Meretrix is here used in a wide sense, and includes Callista, Cytherea, Tivela, Pitaria, etc. Dosinia ( = Artemis). Shell orbicular, compressed, with con- centric ridges or striae. Lunule depressed. Escutcheon narrow. Ligament sunk. Three cardinal teeth in each valve, one anterior lateral in the left valve and two (rudimentary) in the right. Margins smooth. Pallial sinus very deep. Oligocene to present day. Ex. D. exoleta, Coralline Crag to present day. Tellina. Shell oval, elongate, sometimes sub -orbicular, slightly inequivalve, compressed, rounded in front, attenuated behind, and furnished with an oblique fold from the umbo to the MOLLUSCA. LAMELLIBRANCHIA 225 posterior border. Margins of valves smooth. Two cardinal teeth in each valve, and one anterior and one posterior lateral which are often indistinct in the left valve. Ligament external, prominent. Pallial sinus very deep. Jurassic to present day. Ex. T. virgata, Recent ; T. rostralis, Eocene. Psammobia ( = Gari). Shell elongate, sub-equilateral, gaping at the ends, anterior side rounded, posterior side more or less truncate and angular. Surface smooth or with stria?. Ligament external, thick, joined to prominent ridges. Usually two cardinal teeth in each valve, some being bifid. Adductor impressions near the dorsal border. Pallial sinus very deep. Eocene (perhaps Cretaceous) to present day. Ex. P. ferroensis, Coralline Crag to present day. Solen. Shell very long, sub-cylindrical, straight, smooth or finely .striated, the dorsal and ventral margins parallel \ gaping at both extremities. Margins of valves smooth. Umbones at the anterior end. Hinge terminal, with one cardinal tooth in each valve. Ligament long, external. Anterior adductor impression elongated, parallel to the dorsal margin. Pallial sinus short. Eocene (perhaps earlier) to present day. Ex. S. obliquus, Bracklesham Beds ; >S. vagina, Recent. Mactra. Shell oval or trigonal, nearly equilateral, smooth or with concentric striae. Internal ligament in a large triangular pit. External ligament in a groove. In front of the internal ligament- pit is a bifid cardinal tooth (in the form of an inverted V) ; anterior and posterior lateral teeth well-marked, compressed, double in the right valve, single in the left. Adductor impressions semicircular. Pallial sinus round or angular. Cretaceous to present day. Ex. 31. ovalis, Red Crag to present day. My a (fig. 91). Shell oblong, gaping at both ends, particularly at the posterior ; the left valve a little smaller than the right. In the right valve a very small cardinal tooth ; in the left valve a large spoon-like process to which the internal ligament is fixed. Anterior adductor impression elongated. Pallial sinus large and rounded. Eocene to present day. Ex. M. truncata, Pliocene to present day. Corbula. Shell oval, inequi valve, closed, rounded in front, somewhat angular and contracted behind, with a ridge passing from w. p. 15 226 MOLLUSCA. LAMELLIBRANCHIA the umbo to the posterior angle. Surface generally with concentric grooves. Umbones prominent. Right valve larger and more convex than the left, and with a strong cardinal tooth in front of the ligament-pit, and also a posterior cardinal tooth ; left valve with a spoon-like process for the internal ligament, and one posterior cardinal tooth. Adductor impressions well marked. Pallial line slightly sinuous posteriorly. Trias to present day. Ex. C. Jicus, Barton Beds ; C. sulcata, Becent. Panopea. Shell equivalve, inequilateral, oblong, thick, con- centrically striated, gaping at each end, especially at the posterior. Ligament external, on a prominent ridge. One cardinal tooth in each valve. Pallial sinus very deep. Cretaceous to present day. Ex. P. faujasi, Coralline Crag to present day. Saxicava. Shell small, more or less oblong, gaping ; umbones anterior. Ligament external. Teeth absent in the adult, one or two cardinals present in the young. Pallial line not continuous, sinuous. Saxicava bores into rocks, etc. Jurassic to present day. Ex. S. rugosa, Coralline Crag to present day. Pholas. Shell elongate, cylindrical, gaping at both ends. Surface with spiny ridges, best marked in front. On the dorsal region are one or more calcareous plates. No teeth ; no ligament. In the interior, under the umbones, is a process for the insertion of the muscle of the foot. Pallial sinus very deep. Pholas bores into rocks, etc. Lias to present day. Ex. P. cylindrica, Bed Crag ; P. dactylics, Becent. Teredo. Shell more or less globular, gaping at the ends, valves tri-lobed, with concentric stria?. In the interior, under the umbones, is a long narrow plate for the insertion of the pedal muscle. Posterior part covered by a long, calcareous tube, which is sub- cylindrical, straight or curved, and often with partitions. Teredo perforates wood. Jurassic to present day. Ex. T. norvegica, Coral- line Crag to present day. 6. Hinge desmodont. Ligament usually behind the umbones. Two nearly equal adductors. Pallial line usually with a sinus, but sometimes sinuous only. Valves generally somewhat unequal. MOLLUSCA. LAMELLIBRANCHIA 227 Pleuromya. Shell transversely elongated, anterior side short, posterior long and generally compressed, sometimes gaping ; surface with concentric folds. Hinge without teeth, but with a thin pro- jecting lamina at the margin. Ligament partly external. Adductor impressions faintly marked ; pallial sinus deep. Trias to Cre- taceous. Ex. P. do?iacina, Corallian and Kirneridgian. Gresslya. Shell oval, elongate, very inequilateral, smooth or with concentric furrows ; anterior side high and inflated, posterior side narrowing and somewhat compressed. Umbones anterior, close together; lunule sometimes well marked. Right valve a little higher and larger than the left. Adductor impressions shallow ; pallial sinus deep. Behind the umbo of the right valve is a tooth- like projection and an internal plate — the latter appears as a furrow in casts of the shell. Jurassic. Ex. G. gregaria, G. abducta, Inferior Oolite. Ceromya. Shell heart-shaped, inflated, inequilateral, finely granular, with concentric grooves. Left valve not quite so convex as the right. Anterior side short, posterior longer and compressed. Umbones prominent, anterior, curved forward. Hinge thickened, with a ridge behind the umbones ; teeth absent. Pallial line sinuous. Jurassic. Ex. C. concentrica, Inferior Oolite to Corn- brash. Pholadomya. Shell thin, translucent, oblong or oval, ventricose, equivalve, gaping posteriorly and sometimes anteriorly. Anterior side short and rounded. * Surface with radiating ribs crossed by concentric striae. Umbones prominent. Ligament ex- ternal. Hinge without teeth or with a small transverse tubercle. Adductor impressions very faint. Pallial sinus deep. Lias to present day. Ex. P. margaritacea, London Clay. Homomya. Similar to Pholadomya. Without radial ribs ; surface smooth or ornamented with fine granules. Trias to Creta- ceous. Ex. H. gibbosa, Inferior and Great Oolite. Goniomya. Similar to the last two, but with V-shaped ribs pointing ventrally. Lias to Cretaceous. Ex. G. literata, Inferior Oolite to Corallian. Thracia. Shell thin, oblong, compressed, attenuated and gaping posteriorly ; surface smooth or concentrically striated. L"m- 15-2 228 MOLLUSCA. LAMELLIBKANCHIA bones turned a little to the posterior side. Right valve larger than the left. External ligament short, prominent. Hinge thickened behind the umbo forming a stout process or ossicle in each valve to which the ligament is fixed. Adductor impressions small. Pallial sinus not deep. Trias to present day. Ex. T. pubescens, Coralline Crag to present day. 7. Shell thin. Hinge either without teeth or with only imperfectly developed teeth, and without hinge- plate. Ligament external. Two nearly equal adductors. Pallial line simple. This group is a provisional one, and includes primitive Palaeozoic genera, the affinities of which have not yet been determined. Gram my si a. Shell elongate-ovate, very inequilateral, orna- mented with concentric furrows, and one or more radial folds passing from the umbo to the postero-ventral border. Um bones placed anteriorly. Lunule very deep. Hinge-margin thick, without teeth. Anterior adductor very small, posterior large. Pallial line simple. Silurian and Devonian. Ex. G. cingulata, Silurian ; G. hamilton- ensis, Devonian. Cardiola. Shell thin, convex, oval, generally inequilateral ; umbones prominent, incurved. Surface with well-marked radiating and concentric grooves. Hinge-line straight, probably with very small teeth ; ligamental area large, horizontally grooved. Muscular impressions unknown. Silurian and Devonian. Ex. C. interrujpta, Lower Ludlow, etc. Cardiomorpha. Shell thin, smooth or with concentric lines ; sub-quadrate or rounded, inequilateral, very convex. Umbones prominent, curved forwards ; no lunule. Hinge toothless. Ex- ternal ligament small. Adductor impressions shallow ; pallial line simple. Principally Carboniferous. Ex. C. oblonga, Carboniferous Limestone. Edmondia. Shell sub-quadrate or ovate, convex, inequi- lateral ; surface with concentric lines or ridges. Umbones anterior ; no lunule, no escutcheon. Hinge toothless, with a thick ridge posterior to the umbones and separated from the edge of the valve MOLLUSCA. LAMELLIBRANCHIA 229 by a groove. Posterior to the binge is an internal, elongated 'ossicle.' External ligament small. Pallial line simple. Devonian and Carboniferous. Ex. E. unioniformis, Carboniferous Limestone. Sanguinolites. Shell elongate, very inequilateral, with rounded ends, the posterior part usually higher than the anterior part ; surface with concentric ribs or lines. Umbones near the anterior end, with a ridge passing to the lower part of the posterior end ; lunule and escutcheon distinct. Anterior adductor impression large, deep, limited posteriorly by a ridge ; posterior adductor shallow, near the hinge. Pallial line entire. Hinge toothless. Carboniferous. Ex. >S'. angustatus, Carboniferous Limestone. Distribution of the Lamellibranchia All the Lamellibranchs are aquatic animals, and by far the larger number are marine. The marine forms range from the shore-line down to a depth of 2900 fathoms ; they are most abundant in shallow water, and are scarce at depths greater than 500 fathoms, but the following, and a few other genera, have been found below 1500 fathoms: — Nucula, Nuculana, Area, Limopsis, Malletia, Verticordia, Guspiclaria (= Necera). Two genera of Lamellibranchs have been recorded from the Lower Cambrian of North America ; in England the earliest forms appear in the Tremadoc Beds. They are rather rare in the Ordovician, but become fairly numerous in the Silurian, and afterwards gradually in- crease in importance, reaching their maximum at the present day. Many of the genera have a rather extended range in time. In the Palaeozoic formations the Taxodont and Dysodont groups, and primitive dimyarian forms with imperfectly developed hinges, are important. In the Carboniferous period Carbonicola and its allies and the Pectinida? are well represented ; only a very few forms with 230 MOLLUSCA. LAMELLIBRANCHIA a pallial sinus {e.g. Allorisnia) are found. Before the beginning of the Mesozoic period many of the Palaeozoic genera became extinct, and in the Trias a number of new types appear. In the Mesozoic formations Dysodont, Isodont, Schizodont (Trigoniidre), and Desmodont genera are abundant, and the Heterodont forms slowly increase. The Cretaceous period is particularly distinguished by the abundance of Inoceramus, and by the presence of Hip- purites, Radiolites and other allied genera. In the Tertiary period the Heterodont group attains the greatest importance. Fresh water lamellibranchs are generally rare in the Palaeozoic and Mesozoic formations. Probably the earliest form is Archanodon (= Amnigenia) juJcesi from the Old Red Sandstone. In the Coal Measures several species of Carhonicola, Anthracomya, and Naiadites occur. The living type Unio has been found in the Inferior Oolite of Yorkshire, and is fairly common in the Purbeckian and Wealden of the south of England, where it is associated with Cyrena, Freshwater lamellibranchs also occur in the Woolwich Beds, the Oligocene deposits, and in the Pleistocene river-gravels. The principal genera of Lamellibranchs found in the different systems are as follows : Cambrian. Ctenodonta, Glyptarca. Ordovician. Ctenodonta, Cyrtodonta, Glyptarca, Modiolopsis. Silurian. Ctenodonta, Cardiola, Pteria, Pterinea, Ambonyehia, Modiolopsis, Grammy sia. Devonian. Ctenodonta, Cardiola, Pterinea, Aviculopecten, Acti- nopteria, Megalodon, Conocardium. Carboniferous. Nucula, Parallelodon, Posidonomya, Pinna, Conocardium, Leiopteria, subgenera of Pecten, Aviculopecten, MOLLUSCA. LAMELLIBRANCHIA 231 Pterinopecten, Schizodus, Protosekizodus, Carbonicola ( = Anthracosvi), Anthracomya, Edmondia, Sanguinolites, Cardiomorpha. Permian. Bakevellia, Schizodus, Pseudomonotis (Eumicrotis). Trias. Nucida, Nuculana, Palceoneilo, Gervillia, Iloernesia, Pterin, Monotis, Cassianella, Halobia, Ostrea, Pecten (subgenera), Lima, Myophoria, Megalodon, Cardium, Palceocardita. Jurassic. Nucida, Nuculana, Area, Grammatodon, Myoconcha, Modiola, Hippopodium, Pteria, Pseudomonotis, Gervillia, Perna, Pinna, Ostrea, Gryphcea, Alectryonia, Pecten (various subgenera of), Lima, Cardinia, Trigonia, Diceras, Cardium, Unicardium, Astarte, Opis, PacJujrisma, Pleuromya, Ceromya, Gresslya, Pholadomya, Homomya, Goniomya, Thracia. Cretaceous. Nucida, Area, Cucullcea, Modioli, Myoconcha, Gervillia, Inoceramus, Perna, Pteria, Aucella, Ostrea, Exogyra, Alectryonia, Pecten (the subgenera Chlamys, Syncyclonema, Neithea, etc.), Lima, Spondylus, Plicatula, Unio, Trigonia, Hippurites, Radiolites, Sphcerulites, Cardium, Protocardia, Thetironia, Cyprina, Cyrena, Callista, Pleuromya, Pholadomya. Eocene. Nucida, Area, Pectuneulus, Pinna, Pecten {Chlamys, etc.), Ostrea, Chama, Cardium, Venericardia, Cardita, Astarte, Crassa- tellites, Cyprina, Lucina, Cyrena, Corbicula, Meretrix, Psammobia, Tellina, Corbula, Panopcza, Pholadomya. Oligocene. Mytilus, Dreissensia, Ostrea, Cyrena, Corbula, Erodona ( = Potamomya), Lucina, Meretrix, Venus, Psammobia. Pliocene. Nucida, Pectuneulus, Mytilus, Pecten, Chlamys, Cardium, Cardita, Astarte, Cyprina, Lsocardia, Lucina, Venus, Dosinia{ = Ar- temis), Tellina, Mya, Pholas, Thracia. CLASS II. GASTEROPODA Well-known examples of the Gasteropoda are the snail, the whelk, and the cowry. The bilateral symmetry, so characteristic of the lamellibranchs, is generally to a large extent obliterated, owing to the twisting of the visceral 23.2 MOLLUSCA. GASTEROPODA mass and the atrophy of some of the organs on one side of the body. There is a distinct head, which bears one or two pairs of tentacles, and usually also eyes. On the ventral surface of the body is the foot ; this is usually large and sole-like and used for crawling, but in the Heteropods it is in the form of a flattened fin, and in the Pteropods it is wing-like. The mantle is never divided into two lobes. Respiration takes place in some cases through the skin, but generally by means of a lung-cavity or by gills ; the latter are placed in a sac formed by the mantle ; sometimes they are present on both sides of the body, but usually the original left gill has disappeared. In some forms the mantle, at the opening of the gill-sac, is produced into a tube, known as the siphon, by means of which water passes to the gills. The heart is on the dorsal surface, and consists of a ventricle and usually one, but in some cases two auricles. In many forms the gills are placed in front of the heart, but in others behind it. The mouth is at the anterior end of the body ; the anus is occasionally posterior, but as a rule it is placed near the opening of the gill chamber. On the floor of the cavity of the mouth is a dental apparatus, known as the odontophore : this consists of a cartilaginous and muscular ridge on which rests a chitinous ribbon (the radula) ; the radula bears numerous teeth placed in rows, and serves as a rasping organ. The arrangement of the teeth varies in different genera and is of considerable importance in classification, but since the radula has never been definitely recognised in fossil forms, it can only be used by the palaeontologist in the case of genera which have existing representatives. The nervous system consists of ganglia which are connected by nerve-cords. Typically there are three pairs of principal ganglia — the cerebral placed above MOLLUSCA. GASTEROPODA 233 the oesophagus, and the pleural and pedal placed below it ; a visceral nerve-cord, which may bear ganglia, comes off from the pleural ganglia, and forms a loop ventral to the intestine. In some gasteropods (the Euthyneura) this loop is simple, but in others (the Streptoneura) one side is bent over so that the loop forms a figure of 8. Some gasteropods are unisexual, others hermaphrodite. In the majority of the gasteropods a shell is secreted by the mantle ; in a few forms, as for instance the slugs, it is internal, but usually it is external and covers the visceral mass. The shell, except in Chiton and its allies, consists of a single piece, and is hence said to be univalve. In the limpet (Patella) it has the form of a hollow cone ; but in most cases it consists of a long tube, open at one end, and tapering to a point at the other. This tube is coiled into a spiral, generally screw-like, each coil being termed a whorl ; in a few genera (e.g. Vennetus, Siliquaria) the whorls are separated, but as a rule they are in contact (fig. 98), the line between two contiguous whorls being known as the suture (su). All the whorls, except the last, together form the spire (S) of the shell, the point of which is termed the apex (a). The last whorl is nearly always larger — frequently much larger — than the one preceding, and the part of it farthest from the apex is called the base of the shell. The spire varies in form in different genera and species ; sometimes it is composed of a large number of whorls, sometimes of few, and it may be long, short, or depressed; occasionally all the whorls are in one plane. The angle of the spire (spiral angle) consequently varies ; this is measured by lines drawn from the apex to the base of the shell on opposite sides of the exterior of the whorls. The coiling of the shell is usually dextral ; so that when the apex of the shell is pointed away from the observer (as in 234 MOLLUSCA. GASTEROPODA fig. 98) the aperture will be on the right-hand side ; in a few cases it is sinistral, when the aperture will be on the left. Frequently the inner parts of the whorls coalesce, and form an axial pillar extending from the apex to the base of the shell (fig. 98) and known as the columella. In other cases Fig. 98. Longitudinal section of THtonium corrugatum. The upper part of the spire has been partitioned off many times successively. a, apex ; su, suture ; S, spire ; L, outer lip of the aperture ; ac, anterior canal ; pc, posterior canal. (From Woodward.) the inner parts do not fuse, and in the place of the columella there is left a tube-like space, extending from the base of the shell a greater or less distance towards the apex ; this space, which opens at the base of the shell, is called the ■umbilicus. When there is a columella the shell is often MOLLUSCA. GASTEROPODA 235 said to be imperforate, when instead there is an umbilicus it is perforate. The opening of the umbilicus sometimes becomes partly filled up with a shelly growth, known as callus. The animal is attached to the columella by means of a muscle, the contraction of which enables it to withdraw completely into the shell ; but, when not retracted, the coiled visceral mass only is covered by the shell. Usually the cavity of the gasteropod shell is continuous from the apex to the aperture, but in a few cases partitions are thrown across the earlier parts of the shell (fig. 98), forming chambers which remain empty. The form of the aperture varies considerably in different genera and is of great importance in classification ; in shape, it may be circular, oval, elongate, oblong, etc. Its margin is termed the peristome : the outer part forms the outer lip (L), the inner part (that next the columella) the inner lip. As the gasteropod crawls along, the shell is carried on the dorsal surface of its body with the apex directed backward and upward, and the aperture downward ; consequently the part of the aperture farthest from the apex is anterior, the opposite (nearest the apex) is posterior. Sometimes, as in Natica, there is no break in the peristome, and it is then said to be entire or kolostomatous ; in other cases the anterior border is notched or produced into a tube (ac) in which the incurrent siphon is placed, and these forms are said to be siphonostomatous ; sometimes there is also at the posterior border another canal {pc), in which the excurrent or anal siphon is placed. The outer lip may be thin and sharp, or thickened. Sometimes it is curved outwards, and is then said to be reflected] or it is curved inwards — inflected. Its margin may be even, or crenulated, or produced into processes. Many genera have a calcareous or horny plate, known 236 MOLLUSCA. GASTEROPODA as the operculum, attached to the dorsal part of the posterior end of the foot ; this is so arranged that when the animal withdraws into its shell the operculum more or less com- pletely closes the aperture. It has been considered by some as a second valve, but more probably represents the byssus of the lamellibranch. The operculum is seldom preserved fossil ; its form varies considerably in different genera, in some {Turbo) it is of very large size with the inner surface flattened and the outer convex; it may have a spiral structure, and is then sometimes formed of a large number of whorls (midtispiral) as in Trochus, or of a few whorls (paucispiral) as in Littorina. When not spiral it may be concentric, if growth takes place equally all round ; it is then marked with concentric lines, the nucleus being nearly central, as in Viviparus ; or it may be unguiculate or claw-shaped when the nucleus is at the apex as in Fusus. The form of the shell in the spiral gasteropods varies considerably, depending on the arrangement of the whorls in one plane or in a helicoid spiral, on the spiral angle, on the number and shape of the whorls, on the size of the last whorl and whether it conceals the earlier whorls or not. The chief types are the following : — 1. Discoidal ; the whorls all in one plane, as in Planorbis. 2. Conical or trochiform ; conical with a flat base, as in Trochus. 3. Turbinate; conical with a convex base, as in Turbo. 4. Turreted or elongated ; as in Turritella. 5. Fusiform; tapering to each end, as in Fusus. 6. Cylindrical ; as in Pupa. MOLLUSCA. GASTEROPODA 237 7. Globular; as in Natica. 8. Convolute; when the last whorl covers all the others and the aperture is consequently as long as the shell, as in Cyprcea. 9. Auriform; aperture very large and spire very short, as in Haliotis. The surface of the shell is frequently ornamented with spines, knobs, ribs, or striae; these are said to be spiral when they run parallel with the sutures, and transverse when they run across the whorls from suture to suture. In some genera {e.g. Murex) rows of spines, or lamellar processes, extend across all the whorls from the apex to the base of the shell, forming what are termed varices. The surface of the shell in recent gasteropods is generally coloured, often variegated ; in fossil examples the colour has nearly always disappeared, but a few specimens, from various formations, even as early as the Carboniferous, have been found showing the colour more or less perfectly preserved. The shell consists of an outer chitinous layer, and of a calcareous layer which is thick and porcellanous ; in some cases there is also an inner nacreous or pearly layer. The Gasteropoda are divided into two sub-classes : — (1) Isopleura, (2) Anisopleura. SUB-CLASS I. ISOPLEURA The Isopleura, or Polyplacophora, include Chiton and its allies. The body is bilaterally symmetrical and more or less elongated, with the anus at the posterior end. There are numerous (6 to 80) pairs of gills, which are placed in a groove between the foot and the mantle. A nerve-ring surrounds the oesophagus, and from it two 238 MOLLUSCA. GASTEROPODA nerves come off on each side and extend to the posterior end of the body ; ganglia are poorly or not at all developed. The shell consists of eight plates placed in a longitudinal row on the dorsal surface of the body ; each plate usually overlaps the one behind it, and a flexible band or girdle encircles the whole series of plates. All the forms in this group are marine ; they live chiefly in quite shallow water, but a few examples have been found at great depths. Although of great antiquity and represented by a large number of living species, the Isopleura are rarely found fossil. The earliest forms (Priscochiton) occur in the Ordovician ; Helminth ochiton is found in the Silurian ; Gryphochiton in the Carboniferous ; Lepidopleurus, Chiton, and others in the Tertiary. SUB-CLASS II. ANISOPLEUHA The body is asymmetrical, owing to the twisting of the visceral mass. There are not more than two gills. The shell consists of one piece and is usually spiral. There are two orders, (1) Streptoneura, (2) Euthyneura. ORDER I. STREPTONEURA In the Streptoneura (or Prosobranchia) the visceral nerve-cord is twisted into a figure of 8. Usually one gill only is present, and it is placed in front of the heart. An operculum is found in most cases. Patella. Shell conical, oval or sub-circular ; apex sub-central or excentric, nearer the anterior border, often curved forwards ; sur- face with radiating ribs or stripe, rarely smooth. Margin simple or spinose. Muscular impression horse-shoe shaped, open in front. Jurassic (perhaps Palaeozoic also) to present day. Ex. P. vidgata, Pliocene to present day. MOLLUSCA. GASTEROPODA 239 Pleurotomaria. Shell trochifbrm, conical, turbinate, or nearly discoidal ; interior nacreous. Umbilicus present or absent. Aperture sub-quadrate or oval, outer lip sharp, with a slit which, as the shell grows, becomes filled up, leaving a band on the whorls, towards which the lines of growth are directed obliquely backwards. Operculum horny. Ordovician to present day ; common in Jurassic. Ex. P. anglica, Lias ; P. ornata, Inferior Oolite. Murchisonia. Shell turreted, with many, more or less angular whorls, provided with a band as in Pleurotomaria. Aperture oblong, with a slit, and a very short anterior canal. Ordovician to Trias ; mainly Devonian and Carboniferous. Ex. M. vemeuiliana, Carboniferous Limestone. Bellerophon (fig. 99). Shell globular, usually with a narrow umbilicus on each side ; whorls few, embracing, symmetrically coiled in one plane. Aperture sub-circular or oval, with a deep median slit, which is re- placed by a band or keel dividing the shell into two similar parts ; columellar edge often with callus. Ordovician to Permian ; maximum in Carboniferous. ~pig. 99. Bellerophon, from Ex. B. te?udfascia, Carboniferous Lime- the Carboniferous Lime- + stone, showing the slit in the aperture, x % . Emarginula. Shell conical, sur- face generally ornamented with a trellis-work of longitudinal and transverse ribs ; apex not perforated, curved posteriorly. Anterior border with a well-marked slit, which becomes filled up during growth, leaving a raised band. Muscular impression horse-shoe shaped ; no internal septum. Jurassic (perhaps Carboniferous) to present day. Ex. E. Jissura, Coralline Crag to present day. Fissurella. Shell similar to Emarginula, but more or less depressed ; apex perforated and nearer the anterior than the posterior border ; no marginal slit. Muscular impression as in Patella. Fissurella is divided into several sub-genera ; many of the fossil species belong to the sub-genus Fissuridea. Jurassic to present day. Ex. F. crassa, Recent ; F. grceca, Coralline Crag to present day. 240 MOLLUSCA. GASTEROPODA Euomphalus. Shell depressed, discoidal or conical, with a wide and large umbilicus ; whorls convex with a ridge on the upper surface. Aperture polygonal ; outer lip with a slit on its upper surface. Silurian to Trias ; maximum in Carboniferous. Ex. E. pentangulatus, Carboniferous Limestone. Omphalotrochus ( = Horiostoma of some authors). Form similar to Euomphalus. Whorls ornamented with spiral keels and numerous transverse stria? or fine ribs. Aperture without a slit. Ordovician to Carboniferous. Ex. 0. discus, Silurian. Turbo. Shell solid, turbinate or conical, whorls convex, in- terior nacreous. Aperture large, circular, entire, slightly produced anteriorly ; outer lip sharp. Columella curved, flattened. Im- perforate, or with a small umbilicus. Operculum thick, calcareous, exterior convex, interior flat and spiral, nucleus central or sub- central. Jurassic (perhaps also Palaeozoic) to present day. Ex. T. marmoratics, Recent. There are numerous sub-genera. Phasianella. Shell elongated, oval or oblong, smooth, polished, without an umbilicus, interior not nacreous. Aperture oval, entire, rounded anteriorly, angular posteriorly ; outer lip thin, simple, sharp. Columella smooth, flattened. Operculum calcareous, with an excentric nucleus. Upper Cretaceous (or earlier) to present day. Ex. P. australis, Recent ; P. gosauica. Upper Cretaceous. Amberleya. Shell turbinate, elongate, without umbilicus. Whorls ornamented with several spiral keels which are usually spiny or nodular ; between the keels are numerous transverse strise or fine ribs. Base rounded. Aperture sub-oval ; outer lip often crenulated. Trias to Cretaceous (chiefly Jurassic). Ex. A. omata, Inferior Oolite. Cirrus. Shell sinistral, conical or turbinate, or sometimes nearly discoidal, with a very large umbilicus. Spire acute. Whorls irregular, ornamented with strong transverse nodular ribs and finer spiral ribs ; last whorl large. Aperture rounded, entire. Trias to Inferior Oolite. Ex. C. ?wdosus, Inferior Oolite. Trochus. Shell conical, whorls numerous and flat or slightly convex, spire sharp, interior nacreous ; base flat or nearly so, angular at the periphery. Aperture entire, rhornboidal ; outer lip sharp, oblique. Columella twisted, with a prominent anterior tooth-like MOLLUSCA. GASTEROPODA 241 protuberance or a fold. Operculum horny, multispiral, nucleus central. Trias to present day. Ex. T. niloticus, Recent. There are numerous sub-genera. Nerita. Shell thick, solid, ovoid or semi-globose, without an umbilicus ; interior not nacreous. Spire very short. Surface smooth or with spiral ribs. Aperture semicircular, entire ; outer lip thick, the interior generally denticulate ; inner lip flattened, with callus, and a straight denticulate border. Operculum calcareous, nucleus excentric. Cretaceous to present day. Ex. X. ust v lata, Recent ; N. globosa, London Clay and Bracklesham Beds. Neritina. Form similar to Xerita. Shell relatively thin, usually smooth and with colour marking. Outer lip sharp, not thickened, with interior not denticulate ; inner lip flattened, with sharp or finely denticulate border. Eocene (perhaps earlier) to present day. Lives in brackish or fresh water. Ex. X. aperta, Headon Beds ; X. zebra, Recent. Macrochilina ( = 3facrocheilus). Shell elongate-oval, with sharp spire, and last whorl high. Surface smooth or with growth- line. No umbilicus. Aperture ovate, angular behind, sometimes with a shallow anterior canal ; outer lip thin, inner lip with a weak anterior fold. Silurian to Trias. Ex. M. arculata, Devonian. Loxonema. Shell turreted, spire very long ; whorls convex, ornamented with sinuous growth-lines ; sutures deep. No umbilicus. Aperture long, enlarging in front, with shallow canal ; outer lip sharp, sinuous. Silurian to Trias (chiefly Carboniferous). Ex. L. constrictum, Carboniferous. Pseudomelania. Shell elongate, with many nearly flat whorls, without umbilicus, spire long, surface smooth or with growth-lines. Aperture oval, entire, rounded in front, narrowed and angular behind ; outer lip sharp. Columella smooth. Trias to Eocene ; common in Jurassic. Ex. P. heddingtonensis, Corallian Scala ( = Scalaria). Shell turreted, spire elongate; whorls numerous, very convex, sometimes separated, ornamented with strong transverse ribs or sometimes with lamellae, frequently with spiral ribs also. Umbilicus more or less distinct. Aperture circular, entire, margin thickened. Operculum horny, paucispiral. Trias to present day. Ex. S. scalaris, Recent ; >$'. groenlandica, Red Crag to present day. w. p. 16 242 MOLLUSCA. GASTEROPODA Solarium. Shell conical, depressed, angular at the periphery. Aperture entire, sub-quadrate ; lip sharp. Umbilicus wide and deep, limited by a sharp edge which is generally crenulated. Oper- culum horny, spiral. Jurassic to present day. Ex. S. perspectivum, Eecent ; S. canaliculattim, Barton and Bracklesham Beds. Purpuroidea. Shell thick, oval, spire rather short, last whorl inflated. Whorls step-like, flattened below the suture, with tubercles or spines at the angles. Aperture with a small notch anteriorly ; outer lip thin. Inferior Oolite to Upper Cretaceous. Ex. P. nodulata, Great Oolite. Littorina. Shell thick, without a nacreous layer, turbinate, with few whorls, without umbilicus. Aperture rounded, angular behind, outer lip sharp. Columella flattened. Operculum horny, paucispiral. Lias to present day. Ex. L. littorea, Bed Crag to present day. Capulus. Shell conical, with apex bent considerably backward and more or less spirally inrolled. Aperture rounded or irregular. Muscular impression horse-shoe shaped. Lower Palaeozoic to present day. Ex. C. hungaricus, Coralline Crag to present day. Platyceras. Allied to Capulus ; apical part usually more ex- tensively coiled, dextral. Surface smooth, or with concentric striae, or radial folds or spines. Cambrian to Trias. Ex. P. comutum, Silurian. Calyptraea. Shell thin, conical, trochiform, spiral, apex central ; interior with a spiral plate under the apex and attached at the periphery. Aperture nearly circular. Cretaceous to present day. Ex. C. chinensis, Coralline Crag to present day. Natica. Shell oval, globular, generally smooth, spire short, last whorl very large. Aperture semi-lunar or oval, entire ; outer lip sharp, inner lip thickened with callus, not crenulate. Umbilicus usually present, often filled with callus. Operculum of the same size as aperture, horny or calcareous, paucispiral, nucleus excentric. Trias to present day. Ex. N. canrena, Eecent ; N. millepunctata, Coralline Crag to present day. There are numerous sub-genera. Xenophora (= Phorus). Shell conical, low, with flattened or concave base ; periphery of last whorl sharp. Aperture large, oblique, lower part concave, outer lip sharp and oblique. Umbilicus generally small. Whorls flattened, covered with agglutinated foreign bodies. Cretaceous to present day. Ex. X. agglutinans, Barton Beds. MOLLUSCA. GASTEROPODA 243 Viviparus { = PS c*/ v < / ceo s MOLLUSCA. CEPHALOPODA 283 resembles Orthoceras, but the calcareous protoconch and slender marginal siphuncle seem to connect it more closely with the Am- monoids. The wall of the phragmocone (sometimes termed the conotheca) is very thin, and in well-preserved specimens the upper part is found to be produced in front into a large laminar expansion (fig. 121, d) ; this pro- longation is known as c " e J the pro-ostracum, and / >/ of the Belemnite was im- mediately in front of the pro-ostracum. The suck- a v- ' ,N ^^^"'^S* ' t r ers on the arms were *4£r~ i ^> v . I /" provided with horny /,/''- ^ v*s hooks, which are some- ' (^ L times preserved fossil Fig 122 A Belemnites. Lias, Lyme Regis. (fig. 122 J) ; there was a Showing hooks indicating the presence double row of hooks on 0f eight arms (a— h). xf. each arm, but only eight double rows have yet been found in any specimen ; two other arms, with or without hooks, may have been present. The ink-sac and mandibles have also been found in some specimens. The probable positions of the guard, phragmocone and pro-ostracum in the body of the Belemnite are shown in fig. 122, from which it is seen that the guard formed a relatively small part of the entire length of the animal. The 'genus' Belemnites is founded mainly on the characters of the guard, and includes an enormous number of species. Probably if the soft parts were known, they would show such differences as to indicate a number of distinct genera. Lower Lias to Upper Cretaceous. Ex. B. acutus, Lias ; B. oweni, Oxford Clay, etc. ; B. hastatus, Oxford Clay. Belosepia, found in the Eocene, is related to Belemnites, but the guard is considerably reduced in size, and the septa curve forward from the broad siphuncle towards the pro-ostracum. Spirulirostra, from the Eocene and Miocene, is another allied form ; it possesses a small guard ending in a point, and the first part of the phragmo- cone is coiled. In Sepia (Eocene to Recent), the laminae which form the main part of the shell, are believed to represent the septa 284 MOLLUSCA. CEPHALOPODA of tbe phragmocone, whilst the guard is reduced to a small pointed process (or mucro) at the end. Spirula has not been found fossil. Belemnitella. Similar to Belemnites. Guard cylindrical, with a slit at the under side of the alveolus. Distinct vascular impressions on the under surface of the guard. Upper Chalk. Ex. B. mucronata. Actinocamax ( = Atractilites). Similar to Belemnites. Front part of guard either conical or broadly funnel-shaped, and either in contact with the protoconch only or surrounding only the apical part of the phragmocone. Front part of guard often fragile and foliaceous owing to imperfect calcification. Chalk. Ex. A. plenits, Lower Chalk ; A. quadrattis, Upper Chalk. Aulacoceras. Similar to Belemnites. Guard relatively short, with a groove extending down each side. Phragmocone much longer than the guard, with siphuncle at the margin, and septa rather widely separated ; surface of phragmocone with longitudinal lines. Pro-ostracum unknown. Upper Trias. Ex. A. reticulatum. Belemnoteuthis. Guard much reduced, forming a thin layer over the phragmocone, with a groove on the upper side starting from the pointed end. Phragmocone broad, with numerous septa, a marginal siphuncle, and septal necks. Pro-ostracum rela- tively small, seldom preserved. Ten arms bearing hooks. The ink- sac is sometimes found. Chiefly Oxfordian. Ex. B. antiqua. SUB-ORDER II. OCTOPODA There are eight arms only; the suckers are sessile and possess no horny ring. The shell is rudimentary or absent. Octopus and Argonauta are well-known examples of this group. The Octopoda, as might be expected from the general absence of a shell, are very poorly represented in the fossil state ; the earliest known form is Palceoctopus from the Chalk of Lebanon. Argonauta has been found in the Pliocene Beds. MOLLUSCA. CEPHALOPODA 285 Distribution of the Cephalopoda Nautiloidea. At the present day the Nautiloidea are represented by only four species of Nautilus, which are found in the Indian Ocean and the East Indian Archipelago (from Sumatra to Fiji). Nautilus is an active swimmer, and lives in fairly shallow water. This group appears much earlier in the geological series than either the Ammonoidea or the Dibranchia ; the early forms are either straight or slightly curved ; subsequently genera with spiral shells appear. Primitive forms ( Volborthella) are found in the Lower Cambrian ; and two other types {Orthoceras and Cyrtoceras) appear in the Upper Cambrian (Tremadoc Beds). In the Ordo- vician the Nautiloidea are very much better represented than in the Cambrian, and the group attains its maximum development in the Silurian, where the number of species is very great ; it decreases slightly in importance in the Devonian and Carboniferous, and is but poorly represented in the Permian. The only genus which extends beyond the limit of the Palaeozoic period is Orthoceras, which is found in the Trias. Nautilus occurs first in the Trias and is abundant in the Jurassic and Cretaceous ; in the Tertiary it is rare ; Aturia appears in the Eocene and Miocene. Ammonoidea. The geological range of the Ammonoi- dea is shorter than that of the Nautiloidea. The earliest representatives of this sub-order are found in the Devonian; the latest in the Chalk. The group is especially abundant in the Mesozoic formations. Clymenia is limited to the Devonian ; ' goniatites ' also occur in the rocks of that system, but are more numerous in the Carboniferous — 286 MOLLCJSCA. CEPHALOPODA Glyphioceras being especially characteristic of the latter. Ammonites appear first in Permian deposits ; throughout the Mesozoic rocks they are extremely abundant, attaining their maximum in the Lias. In the Cretaceous there is a remarkable development of more or less completely un- coiled Ammonoids, e.g., Hamites, Macroscaphites (fig. 115), Bacidites, Crioceras, and Scaphites ; and there is evidence showing that, in most cases, these 'genera' include species which have descended from more than one genus of am- monites. The abrupt disappearance of the Ammonoidea at the end of the Cretaceous period is remarkable. Dibranchia. The Dibranchia are more numerous and more varied in existing seas than they were at any former period. Some forms are pelagic, others abyssal, but the larger number are found in littoral regions and are dis- tributed in provinces similar to those of other molluscs (p. 251); typical littoral genera are Octopus, Sepia, and Loligo. The Dibranchia are unknown in the Palaeozoic forma- tions, the earliest examples {Aulacoceras, Phragmoteuthis) appearing in the Trias. Belemnites is the chief form in the Jurassic and Cretaceous, and is especially abundant in the clayey beds. Geoteuthis occurs in the Lias; and Belemnoteuthis, Plesioteuthis, etc. in the Upper Jurassic. Belemnitella is limited to the Upper Chalk. Dibranchs are relatively rare in the Eocene and Miocene ; Belemnites is absent, but is represented by Belosepia and Spiruli?*ostra. The principal genera of Cephalopoda are : Cambrian. Volborthella in the Lower Cambrian ; Orthoceras and Cyrtoceras in the Tremadoc Beds. Ordovician. Orthoceras, Cyrtoceras, Endoceras, Piloceras, Cono- ceras. MOLLUSCA. CEPHALOPODA 287 Silurian. Orthoceras, Cyrtoceras, Actinoceras, G omphoceras, Phragmoceras, Trockoceras, Ascoceras, Ophidioceras. Devonian. Nautiloidea : — Orthoceras, Cyrtoceras. Animonoi- dea : — Clymenia, Bactrites, Mimoceras, Anarcestes, Tornoceras. Carboniferous. Nautiloidea : — Orthoceras, Cyrtoceras, Actinoceras, Poterioceras, Discites, Vesti nautilus, C&lonautilus, Pleuronautilus, Temnocheilus. Ammonoidea : — Glyphioceras, Gastrioceras, Pro- lecanites. Permian. Nautiloidea : — Orthoceras, Temnocheilus. Ammo- noidea : — Medlicottia, Cyclolobus. Trias. Nautiloidea : — Nautilus, Orthoceras. Ammonoidea : — Pinacoceras, Ceratites, Trachyceras, Ptychites, Arcestes, Cladiscites, Monophyllites, Rhacophyllites. Dibranchia : — Aulacoceras, Atrac- tites, Phragmoteuthis. Lias. Nautiloidea : — Nautilus. Ammonoidea : — Phylloceras, Lytoceras, Psiloceras, Arietites, JEgoce?'as, Liparoceras, Oxynoticeras, Amaltheus, Schlotheimia, Harpoceras, Hildoceras, Cosloceras, Dacty- lioceras. Dibranchia : — Belemnites, Xiphoteuthis, Geoteuthis. Oolites. Nautiloidea : — Nautilus. Ammonoidea : — Ludwigia, Leioceras, Haploceras, Stepheoceras, Macrocephalites, Cardioceras, Quenstedtoceras, Perisphinctes, Peltoceras, Aspidoceras, Parkinsonia, Cosmoceras. Dibranchia : — Belemnites, Belemnoteuthis, Acantho- teuthis. Lower Cretaceous. Nautiloidea : — Nautilus. Ammonoidea : — Macroscaphites, Hamites, Holcostephanus, Desmoceras, Parahoplites, Douvilleiceras, Crioceras. Dibranchia : — Belemnites. Upper Cretaceous. Nautiloidea : — Nautilus. Ammonoidea : — Hamites, Turrilites, Baculites, Desmoceras, Pachydiscus, Hoplites, Acanthoceras, Scaphites, Schloenbachia. Dibranchia : — Belemnites, Belemnitella, Actinocamax. Eocene. Nautiloidea: — Nautilus, Aturia. Dibranchia : — Belo- sepia, Beloptera, Spirulirostra. PHYLUM ARTHROPOD A Classes (1. 2. 3. 4. Sub-classes Trilobita. Branchiopoda. Ostracoda. Copepoda (not fossil). Orders 1. Crustacea . 5. Cirripedia. 2. 3. 4. Leptostraca. Syncarida. Schizopoda. Cumacea (not fossil). u. Malacostraca < 5. Tanaidacea (not fossil) 6. Isopoda. 7. Amphipoda. 8. .9. Stomatopoda. Decapoda. 2. Onychophora (not fossil). 3. Myriapoda. a. 2. 3. Aptera. Orthoptera. Neuroptera. 4. < 4. 5. 6. 7. Lepidoptera. Coleoptera. Hemiptera. Diptera. 8. Hymenoptera. ( 1. Merostomata /l. 2. Xiphosura. Eurypterida. Scorpionida. Pedipalpi. 5. Arachnida -< 3. Araneida. i 2. Euarachnida - 4. 5. u. Pseudoscorpionida. Phalangida Acarina. ARTHROPODA 289 The Arthropods have a bilaterally symmetrical body, formed of a series of segments, but the segments are not all alike, and some are fused together. Some, or all of the segments, bear a pair of jointed appendages or limbs, those near the mouth being modified to serve as jaws. A chitinous exoskeleton is always present, and is often strengthened by the deposition of carbonate or phosphate of lime ; between the segments the integument remains soft and flexible, so that movement of the parts of the body is rendered possible. A heart is found in most forms ; it is placed dorsally, and is provided with paired slits, termed ostia. The body-cavity contains blood. In some forms respiration takes place by means of the general surface of the body ; others are provided with special organs — gills (or branchiae), tracheae, or lung-books. The gills are generally thin projections of the skin borne by some of the appendages ; the tracheae are long, branching tubes, filled with air, which penetrate all parts of the body and open to the exterior; the lung-books are chambers containing leaf-like folds of the skin. The nervous system consists of a supra-oesophageal ganglion or brain, connected by a ring round the oesophagus, with a ventral cord, usually provided with ganglia, and placed beneath the intestine. The sexes are separate in the majority of forms. The Arthropoda are divided into the following Classes: — (1) Crustacea, (2) Onychophora, (3) Myriapoda, (4) In- secta, (5) Arachnida. The Onychophora include one genus only — Peripatus, which has not been found fossil. CLASS I. CRUSTACEA The Crustacea are mainly aquatic animals, and are abundant as fossils; they breathe generally by means of w. p. 19 290 ARTHROPODA. CRUSTACEA gills, but in some cases respiration takes place through the general surface of the body. The chitinous exo- skeleton is frequently hardened by a calcareous deposit, — hence the name Crustacea. Segmentation is usually well marked, but in the Ostracoda is shown by the appendages only. The exoskeleton of a segment consists of a dorsal part, the tergum, and a ventral part, the sternum. Three regions may be distinguished in the body : — the head, the thorax, and the abdomen; but in the lower forms the abdomen is often not clearly marked off from the thorax. In the head there are five segments fused together, but ex- ternally these (except in Trilobites) are indicated only by the appendages. The number of segments in the thorax and abdomen is variable in the lower Crustacea, but is con- stant in the Malacostraca. In many forms some or all of the segments of the thorax fuse with those of the head, forming a cephalothorax. In many Crustacea there is a dorsal shield or carapace which covers part, or sometimes the whole, of the body, and originates as an outgrowth from the pos- terior margin of the dorsal part of the head. The head usually bears five pairs of appendages, viz. : — two pairs of feelers (the antennules and antennae), one of mandibles, and two of maxillae ; the first two pairs are in front of the mouth. The thorax is also provided with appendages, and often the abdomen too. The mandibles and maxillae, and frequently some of the anterior thoracic appendages, serve as jaws. The Crustacean appendage is typically biramous, consisting of a basal part (the protopodite) bear- ing two branches — the inner called the endopodite, and the outer termed the exopodite. The protopodite usually consists of two segments — a proximal or coxopodite, and a distal or basipodite. The mouth is on the under surface of the head, and the anus is on the last segment (the ARTHROPODA. CRUSTACEA 291 telson) of the abdomen. Eyes are generally present, commonly a pair of compound eyes, and sometimes a median simple eye. The sexes are separate except in most of the cirripedes and in some parasitic isopods. In the Malacostraca the genital apertures are on the sixth thoracic segment in the male, and on the eighth in the female ; in the Entomostraca the position of the apertures is variable. In some Crustacea development is direct, that is to say, the young individual has the same form as the adult; but generally this is not the case, the young undergoing metamorphosis before reaching the adult stage. The two chief larval forms are known as the nauplius and the zocea. In the nauplius the body is unsegmented, and possesses three pairs of appendages representing the two pairs of antennae and the mandibles. In the zoaea stage some of the thoracic appendages are present also, and the abdomen is segmented but possesses no appendages. The Crustacea are divided into six sub-classes: — (1) Trilobita, (2) Branchiopoda, (3) Ostracoda, (4) Cope- poda, (5) Cirripedia, (6) Malacostraca. The Copepods are not definitely known as fossils. The first five sub-classes are usually grouped together as the Entomostraca, but they differ considerably from one another and are not united by the possession of important features common to all. In comparison with the Malacostraca they are generally of simple organisation, usually with the number of segments in the thorax and abdomen varying widely, and (with the exception of the Trilobita) they are generally of small size, with the abdomen usually ending in a caudal fork, and often without a clear differentiation of the trunk into thorax and abdomen. A median unpaired eye is usually present. 19—2 292 CRUSTACEA. TRILOBITA SUB-CLASS I. TRILOBITA The Trilobites derive their name from the fact that the body is divided into three parts, by means of two furrows, which extend from the anterior to the posterior extremi- ties ; this trilobation is usually conspicuous, but in a few genera {e.g. Homalonotus, Illamus), it is indistinct or almost obsolete. The body is oval in outline, and flattened from above downwards ; it consists of the head (fig. 123 A), the thorax (B), and the pygidium or abdomen (C). The Fig. 123. Calymene tuberculata, from the Wenlock Limestone. Dorsal surface. A, head; B, thorax; C, pygidium or abdomen, a, glabella ; a', axial furrow ; b, one of the glabella furrows ; b', neck-furrow, behind which is the neck-ring ; d, facial suture ; e, eye ; /, free cheek ; g, fixed cheek ; h, genal angle ; i, axis of thorax ; k, pleura. Natural size. CRUSTACEA. TRILOBITA 293 segments of the head and of the pygidium are fused together, but those of the thorax remain free. Traces of the alimentary canal are sometimes found in the middle or axial part of the Trilobite. The dorsal surface of the body is protected by a strong, calcareous exoskeleton. The part which covers the head is known as the head-shield or cephalic shield, and is usually semicircular or triangular in shape ; in it may be distinguished a median and two lateral portions ; the former is the more convex and is termed the glabella (a), the latter are the cheeks. The glabella is marked off from the cheeks by means of a furrow on each side, known as the axial furrow (a). The form and relative size of the glabella vary in different genera; in some it extends quite to the anterior margin of the head-shield, in others only a part of the way (fig. 131); sometimes it is wider behind than in front ; in other cases it is wider anteriorly, or it may be of uniform width throughout ; its convexity also varies considerably — it may be nearly flat, but is some- times pear-shaped or spheroidal. The segmentation of the head is indicated by transverse furrows on the glabella (b), — often three on each side ; in some cases the opposite furrows from the two sides meet at the middle of the glabella. On the posterior part of the glabella there is another furrow, which extends quite across it and is con- tinued on to the cheeks ; this is known as the neck-furrow (b'), and the segment of the glabella behind it is the neck- ring. These furrows indicate the existence of five seg- ments in the head. In primitive trilobites all the furrows are distinct, but in others some, especially the anterior furrows, become indistinct or obsolete. The cheeks are more or less triangular in shape, and usually less convex than the glabella ; they are frequently 294 CRUSTACEA. TRILOBITA bordered by a flattened or concave margin which in Trinucleus is very broad and highly ornamented. The posterior angles of the cheeks, known as the genal angles (h), may be rounded (e.g. Calymene), but are often pointed or produced into spines, the genal spines (e.g. Paradoxides, fig. 130). Each cheek is usually divided into two portions by a suture (the facial suture, d) ; the inner part — that between the facial suture and the glabella — is termed the fixed cheek (g) and is immovable ; the outer part, known as the free cheek (/), is slightly movable on the fixed cheek. The course of the facial suture varies in different forms : it may commence on the posterior border inside the genal angle (fig. 132), or at or near the genal angle (h), or on the lateral border in front of the genal angle ; it passes inwards to the eye and then bends forwards, and may be continuous with the suture of the other cheek in front of the glabella, or it may cut the anterior margin of the head-shield, in which case it is sometimes united with the suture of the other side on the inferior surface of the head (fig. 125, d). When the sutures are continuous in front of the glabella it is evident that the cheeks will also be continuous. Since the position of the facial suture varies in different genera the relative sizes of the fixed and free cheeks will obviously vary too ; thus in Illcenus the free cheek is very narrow, in Phillipsia very broad. Owing to the fusion of the fixed and free cheeks the facial suture is sometimes absent (e.g. some species of Acidaspis)\ this is probably also the case in Agnostus, Microdiscus and a few other genera ; but according to Beecher a facial suture is present in Agnostus and is either at the margin or on the ventral surface of the cephalic shield, and the free cheek is then on the ventral surface ; this view, however, is not accepted by Lindstrom and Holm. CRUSTACEA. TRILOBITA 295 The eyes (fig. 123, e) are on the upper surface of the head, one on each free cheek in the angle made by the facial suture ; they are more or less conical with the summit truncated or rounded, and with the visual surface on the external part. The eyes are usually compound, and in most cases con- sist of a large number of lenses — in FiS- 12^- Mglina bi- P . nodosa, Arenig Beds. Kemopieundes the number is stated Natural size, to be 15,000. Usually the lenses are biconvex or globular and adjacent to one another, but in Phacops and its sub-genera the eyes are more highly developed, the lenses being separated by portions of the cephalic shield so that each appears to rest in a separate socket. The eye is entirely on the free cheek, but rests on a lobe or buttress on the adjacent part of the fixed cheek. In a few Trilobites the eyes are said to be simple ; for example, in Harpes each eye usually consists of two or three lenses only; but it is probable that in such cases the eye is a degenerate form of compound eye rather than a simple eye. In a few genera (Agnostics, Microdiscus, Ampyx) eyes are absent; in JEglina (fig. 124) they are unusually large, occupying the greater part of the free cheeks. Many of the Cambrian Trilobites which have usually been regarded as possessing eyes (Paradoxides, Olenus, Sao) are considered by Lindstrom to have been blind, since the eye-like lobe, which is present, shows no indication of structure and differs in development from that of the eyes, which always appear in close connexion with the facial suture. In many Cambrian and some few later Trilobites a thread-like ridge, called the eye-line, extends from the eye to the glabella. 296 CRUSTACEA. TRILOBITA Fig. 125. Calymene tuberculata, Silu- rian. Ventral surface of head. a, hypostome ; b, marginal rim ; c, facial suture ; d, transverse su- ture ; e, rostral plate. (After Barrande.) Natural size. The head-shield is continued on the under surface of the head as a reflexed border or marginal rim (fig. 125, b); sometimes the facial sutures (c) are continued across this bor- der, and they may be joined by a transverse suture (d). Attached to the border in the median line is a plate (a), usually oval or shield-shaped, situated just in front of the mouth and known as the hypostome or labrum (fig. 126). Just behind the mouth is the small lower lip-plate or metastoma (fig. 128 A, m), which, up to the present time, has been found in Tri- arthrus only. In many Trilobites a small oval or elliptical area, sometimes slightly raised like a tubercle, in other cases depressed, is found on each side of the hypo- stome just behind the middle of its outer surface (fig. 126); these maculce are sometimes entirely smooth, but in other cases a part, or the whole of the surface, shows a structure similar to that of the compound eyes on the dorsal surface of the head, and such were probably visual organs. Macula? are not known to occur in any other Crustacea. The thorax (fig. 123 B) consists of a series of segments, which vary in number from two to twenty-nine, and are movable upon one another, in some cases sufficiently to Fig. 126. Hypostome of Asaphus tyrannus, from the Llandeilo Beds. Re- duced. CRUSTACEA. TRILOBITA 297 enable the animal to roll itself up like a woodlouse. Each segment is divided into a median and two lateral parts by means of two furrows. The median or axial part is more convex than the lateral, and forms the axis (i), the lateral parts being known as the pleiwce (k). The anterior part (fig. 127,c) of the axis of each segment is not visible when the animal is unrolled, since it _. .,_ _ , „ „ , .big. 127. Dorsal surface of a thoracic IS bent down and IS Over- segment of Asaphus expansus. a, lapped by the preceding ring of ax^; &, groove; c, articular rr J i o portion ; a, furrow between axis and Segment, for which it pleura ; d—g, pleura ; e, fulcrum ; ( . . ■, P f, facet ; h, groove on pleura, forms an articular surface. The pleurae in some genera possess a longitudinal ridge, in others a groove (h), or both ridge and groove may occur; a few forms have plane pleurae. Each pleura, at some distance from the axis, is curved downwards and usually also backwards ; the point where this curvature occurs is known as the fulcrum (e) ; sometimes the outer part of each pleura overlaps the anterior part of the suc- ceeding one, and then the front part of the pleura beyond the fulcrum may be smooth and flattened so as to form an articulating surface or facet (f). The terminations of the pleurae are in some cases rounded (fig. 127), in others pointed or produced into spines (fig. 130). The pygidium or abdomen (fig. 123 C) is commonly triangular or semicircular in shape, and is formed of a variable number of segments, which differ from -those of the thorax in being fused together and immovable ; on the dorsal surface the segmentation is shown by grooves only. The pygidium, like the thorax, is divided into a median part or axis, and lateral portions. The axis may reach quite to the posterior extremity or only part of the 298 CRUSTACEA. TRILOBITA way, and it tapers more rapidly than the axis of the thorax ; in Bronteus it is very short. The margin of the pygidium may be even or entire, or may be provided with a posterior spine or with lateral spines. This margin is bent under so as to form a border on the ventral surface similar to that on the ventral surface of the head. For a long time the appendages of the Trilobites were unknown. In the great majority of specimens, when the under surface is exposed, the only parts which are found to be preserved are the hypostome and the reflexed borders of the dorsal exoskeleton. But in rolled-up specimens of Galymene and Cheirurus, Walcott showed, by means of thin sections, that jointed appendages are present on the head, thorax and pygidium, and that the ventral surface of the body is formed of a thin, uncalcified cuticle, strengthened by transverse arches. More recently specimens in which the body is not rolled up, showing clearly the ventral surface with the appendages, have been obtained from the Utica Slate near Rome (New York), and have been fully described by Beecher. The most important of these belong to the genus Triarthrus (fig. 128). Each segment of the body, excluding the last (or anal), is found to bear one pair of appendages, which, with the exception of the first, are biramous. On the head there are five pairs of append- ages. The first are the long antennae which consist of a large basal joint and numerous short conical joints and are attached on each side of the hypostome (h); these appear to be the only appendages in front of the mouth, and are considered by Beecher to represent the anten- nules (or anterior antennae) of other Crustacea. The remaining four pairs of appendages of the head are biramous and all appear to have nearly the same form but CRUSTACEA. TRILOBITA 299 increase in size backwards : the second pair are considered to represent the antennas, the third the mandibles, and the fourth and fifth pairs the maxillae of other Crustacea. Each maxilla consists of a large basal joint (the coxopodite) which bears a stout endopodite and a slender exopodite; the latter carries a row of hairs or setce ; the inner edge of the coxopodite is toothed and served as a jaw (gnatho- base); whilst the endopodite and exopodite assisted in locomotion. Fig. 128. Triarthrus becki, from theUtica Slate (Ordovician) near Rome, New York. (After Beecher.) A, view of the ventral surface showing appendages, etc. h, hypo- stome ; m, metastoma. x If. B, diagrammatic section through the second thoracic segment. a, endopodite ; b, exopodite. C, dorsal view of second thoracic leg. a, endopodite ; b, exopo- dite ; c, coxopodite with gnathobase. Enlarged. 300 CKUSTACEA. TRILOBITA The appendages of the thorax are long, but gradually decrease in size backwards, and consist of a coxopodite (fig. 128 C, c) bearing the endopodite (a) and the exopo- dite (b) which are of nearly equal length. The endopodite is formed of six joints, and probably served as a swimming organ. The exopodite consists of a long basal joint fol- lowed by a part consisting of numerous short joints ; it bears setae along its posterior edge and was probably adapted for crawling. The inner prolongations of the coxopodites served as jaws. The limbs in each pair are widely separated, and in each segment the ventral cuticle between their bases is strengthened by a median longi- tudinal ridge and one or two oblique ridges on each side. On the posterior part of the thorax some of the joints of the endopodites become flattened. The appendages of the pygidium are similar to those on the posterior part of the thorax, but are more distinctly leaf-like owing to the flattening and expansion of the first segments of the endopodite which bear setae ; the exopo- dite is slender. The anal opening is on the last segment (or telson) near the end of the pygidium. In some fine-grained deposits, especially in the Lower Palaeozoic rocks of Bohemia, the larval forms of Trilobites are found well preserved, and by obtaining specimens of different ages it is possible to trace out the changes which occurred in the development of the individual. In the earliest stage (fig. 129 A), called the protaspis by Beecher, the body is discoid or ovate in form, and consists of a large cephalic region and a small pygidial part ; the axis is distinct, and is marked by furrows ; eyes, when present, are at or near the outer front margins of the shield (fig. 129 E), and the free cheek, if visible on the dorsal surface, is narrow (G). The glabella usually reaches the front CRUSTACEA. TRILOBITA 301 margin of the head. In later stages the pygidium becomes more distinct and increases in size ; and the thoracic seg- ments are gradually introduced between the head and the pygidium (C, D). At the same time the eyes move back- wards and inwards until they attain their adult position, and the free cheeks increase in size (H). The glabella Fig. 129. Development of Trilobites. (After Barrande.) A — D. Sao hirsuta, Cambrian, Bohemia. A, earliest stage (protaspis), x 12. B, later stage with three segments behind the head, x 12. C, with more distinct glabella furrows, and four segments behind the head, x 12. D, with six segments behind the head, x 10. E — H. Phacops (Odontochile) socialis, Ordovician, Bohemia, x about 8. E, earliest known stage, with eyes at the margin, and three segments behind the head. F, later stage with more distinct furrows on the glabella, and four segments behind the head. G, with eyes moved inward, and narrow free cheeks ; six segments behind the head. H, free cheeks relatively larger and eight segments behind the head. often becomes rounded in front and relatively shorter ; its furrows become more distinct, indicating the existence of five cephalic segments. Since in the earliest stages of all Trilobites the free cheeks are either absent from the dorsal surface or are narrow, Beecher regards the Trilobites which retain this character in the adult state as more primitive than those in which the free cheek becomes 302 CRUSTACEA. TRILOBITA relatively large and the fixed cheek narrow. Beecher considers that the protaspis of Trilobites corresponds to one of the nauplius stages (the metanauplius) of recent Crustacea, but that view is not accepted by Kingsley. The possession of antennae, the biramous character of the other appendages, and the presence of five cephalic segments, show that the Trilobites belong to the Crustacea. The great variability in the number of segments in the thorax and pygidium, the leaf-like character of the ap- pendages on the posterior part of the body, the large hypo- stome, and the gnathobases on the thoracic appendages seem to indicate that the Trilobites are related to the Phyllopod division of the Branchiopoda (p. 312), and es- pecially to Apus and Branchipus. But the Trilobites differ from the Phyllopods in the trilobation of the body, in the occurrence of a facial suture, in the posterior segments being fused together to form a pygidium, and in the absence of a caudal fork. In the character of their append- ages the Trilobites are more primitive than any other Crustacea, since all except the first pair are very similar in structure and show but little specialisation in different regions of the body, and all are deeply biramous. Other primitive characters are seen in the indication of segmen- tation on the dorsal surface of the head, and in the presence of a pair of appendages on every segment of the body except the last. The Trilobites differ from most other Crustacea in having only one pair of antenniform appendages. The Trilobites show some resemblance to the Xiphosura (p. 338), and before their appendages were known, they were thought by some writers to be allied to that group. But they are clearly separated from the Xiphosura by the presence of five cephalic segments, the biramous character of the appendages, the occurrence of antennae and a CRUSTACEA. TRILOBITA 303 hypostome, and by the structure of the eyes, as well as by the absence of a genital operculum, and the presence of one pair of eyes only. Agnostus. Body small, head-shield and pygidium similar in form and size ; eyes and facial suture absent ; glabella does not reach the anterior border of the head, and has a small lobe at each of the posterior angles. Thorax formed of 2 segments, axis wide, pleurae grooved. Segmentation not shown on the lateral parts of the pygidium. Olenellus Beds to Bala Beds. Ex. A. piriformis, Lingula Flags. Microdiscus. Similar to Agnostus but with 3 or 4 segments in the thorax, and axis of pygidium with numerous distinct segments. Olenellus Beds to Lingula Flags. Ex. M. punctatus, Lingula Flags. Trinucleus. Head-shield large, with long genal spines, and a broad flat, ornamented border ; glabella inflated, pyriform, furrows sometimes absent. Eyes generally absent. Facial suture absent or indistinct. Thorax formed of 6 segments, pleurae grooved, straight, but slightly curved near their extremities. Pygidium short, tri- angular, margin entire. Arenig to Bala Beds. Ex. T concentricus, Bala Beds. Ampyx. Similar to Trinucleus. Head-shield triangular, without a border, and with a long straight spine given off from the front of the glabella ; facial sutures near the external margin, not continuous in front ; free cheeks very narrow. Arenig to Wenlock Beds (chiefly Ordovician, only one species in the Silurian). Ex. A. nudus, Llandeilo Beds. Harpes. Resembling Trinucleus, but border of head- shield broader, finely punctate, and extended posteriorly to near the end of the thorax instead of bearing narrow genal spines. Glabella short, convex, not expanded in front. Eyes consist of 2 or 3 lenses, and are usually joined to the front part of glabella by an eye-line. Thorax with 22 to 29 segments ; axis narrow, pleurae long, grooved. Ordovician to Devonian. Ex. H. ungula, Ordovician. Paradoxides (fig. 130). Body large, elongated, narrowed posteriorly. Head-shield broad, semicircular, with a border, and long genal spines ; glabella broad in front, with 2 to 4 furrows on each side, some of which are continuous across. Facial sutures 304 CRUSTACEA. TRTLOBITA extend from the posterior to the anterior border. Eyes large and arched. Thorax long, of 16 to 20 segments ; pleurae grooved and produced into long backwardly-directed spines. Pygidium very small, plate-like, its axis with 2 to 8 segments. Middle Cambrian. Ex. P. davidis, Menevian ; P. bohemicus, Cambrian. Oienellus. Similar to Paradoxides same width throughout ; facial sutures not visible ; ' eyes ' large, joined to the glabella ; 13 to 18 segments in the thorax. Some forms have spines on the axis of one or more segments of the thorax and pygidium. In some species there are no lateral lobes on the pygidium. Lower Cambrian. This genus is divided into four sub-genera : — (1) Oienellus (restricted) ; pygidium spine- like, without lateral lobes. Ex. 0. thompsoni. (2) Mesonacis ; pygidium large, with lateral lobes, spines on some segments of the axis of thorax or pygi- dium. Ex. M. vermontana. (3) Holmia ; with a row of spines down the axis of the body — the neck-spine often long ; pygidium small, plate-like. JZx.H.callavei. (4) Ole?ielloides, Ex. 0. armatus. Glabella of nearly the Fig. 130. Paradoxides davidis, from the Menevian Beds, x £. Conocoryphe ( = Conocephalites). Head-shield semicircular, with genal spines (not always preserved) ; axial furrows deep, glabella narrow in front and with 3 or 4 backwardly-directed furrows and well-marked neck-furrow ; free cheeks narrow ; eyes absent. Facial sutures begin just within the genal angles, and cut the front margin. Hypostome convex, formed of a central oval portion sur- rounded by a narrow border. Thorax with 14 or 15 segments ; pleurae grooved. Pygidium small, margin entire, axis with from CRUSTACEA. TRILOBITA 305 Fig. 131. Olenus cataractes, from the Lingula Flags. Natural size. 2 to 8 segments. Lower Cambrian to Tremadoc Beds. Ex. C. li/elli, C. sulzeri, Lower Cambrian. Olenus (fig. 131). Body oval ; head-shield larger than the pygidium, with a narrow border, and with genal spines ; glabella not reaching the anterior border, and not expanding in front, usually with three pairs of fur- rows ; facial sutures extend from the posterior margin (near the genal angle) to the front border ; eyes a little in front of the middle of the cheeks, and united to the front of the glabella by an eye-line. Thorax of from 12 to 15 (typically 14) segments ; axis narrow, pleurae with short points. Pygidium small, with 3 or 4 segments indicated on the axis, and with entire border. Lingula Flags to Tremadoc Beds. Ex. 0. gibbosus, 0. cataractes, Lingula Flags. Parabolina, Peltura, Parabolinella, Leptoplastus, Eurycare, and Sph&rophthalmus are related to Olenus and usually regarded as sub-genera of it. Angelina. Body oval. Head-shield with long genal spines, glabella parabolic, without furrows; eyes small, near the middle of the cheeks. Thorax with 14 or 15 segments, pleura? facetted. Pygidium short, margin provided with two teeth, axis of 4 or 5 segments. Tremadoc Beds. Ex. A. sedgivicki. Calymene (fig. 123). Head-shield semicircular, genal angles rounded, occasionally pointed ; glabella inflated, broadest behind, with three pairs of lateral furrows separating three globular lobes on each side. Eyes small, prominent. Facial sutures extending from the genal angles to the anterior border, where they are connected by a transverse suture below the margin. Thorax of 13 segments, axis prominent, pleurae grooved and facetted. Pygidium with 6 to 11 segments, margin entire. Arenig to Upper Ludlow. Ex. C. tuberculata, Wenlock Limestone. HomalonotllS. Body large, elongated, with indistinct triloba- tion. Head-shield broad, genal angles rounded, furrows on the gla- bella indistinct or absent. Eyes small. Facial suture passing from w. p. 20 306 CRUSTACEA. TRILOBITA the genal angles to the front margin, and often continuous in front. Thorax with 13 segments ; axis wide, not well marked. Pygidium triangular, axis with 10 to 14 segments. Arenig to Devonian. Ex. H. delpkinocepkalus, Wenlock Beds ; H. bisulcatus, Ordovician. Ogygla. Body oval, nearly flat. Head-shield large, semi- circular, with a flattened border ; glabella distinct, wider in front, with 4 or 5 lateral furrows. Eyes large. Facial suture passes from the posterior border to the front margin, and is generally con- tinuous at the margin. Free cheeks large. Hypostome not notched. Thorax consisting of 8 segments, axis narrow, distinct ; pleurae grooved, usually with pointed ends. Pygidium large, semicircular, margin entire, axis of numerous segments. Tremadoc to Llandeilo Beds. Ex. 0. buchi, Llandeilo Beds. Asaphus (figs. 126, 132). Body oval, surface smooth or with striae. Head-shield large, semicircular with a flattened border, genal angles rounded or spinose ; glabella indistinctly defined, wide in front, with indistinct lateral furrows. Eyes large. Facial sutures pass from the posterior to the anterior margin and are generally continuous at the front margin. Free cheeks large. Hy- postome notched posteriorly. Thorax formed of 8 segments, axis rather broad, pleurae obliquely grooved, with rounded extremities. Pygidium of about the same size as the head, rounded, formed of numerous segments; margin entire. Tremadoc to Bala Beds. Ex. A. ty- rannus, Llandeilo. Sub-genus Asa- phellus : hypostome not notched. Tremadoc Beds. Ex. A . homfrayi. Illaenus. Body oval, convex. Head-shield large, semicircular ; glabella indistinctly limited except near the posterior end, without furrows externally. Eyes remote from one another. Facial sutures commence on the posterior border, cut the anterior border in front of eye, and unite on the inferior sur- face. Free cheeks small. Thorax with usually 10 segments, axis Fig. 132. Asaphus tyrannus, from the Llandeilo Beds. x £. CRUSTACEA. TRILOBITA 307 broad, pleurae neither grooved nor ridged. Pygidium large, semi- circular, axis indistinct, segments not visible externally. Arenig to Wenlock. Ex. /. davisi, I. bowmanni, Bala Beds. iEglina (fig. 124). Head-shield large ; glabella large, convex, projecting beyond the margin in front. Cheeks narrow ; eyes very large, occupying nearly all the free cheeks. Facial sutures discon- tinuous, nearly parallel with the axis of the body. Thorax with 5 or 6 segments, axis broad, pleurae grooved. Pygidium rounded, axis short. Arenig to Bala Beds. Ex. JE. binodosa, Arenig Beds. Bronteus. Head-shield large, semicircular, genal angles pointed. Glabella expanding rapidly in front, with 3 lateral furrows in some species, none in others. Facial sutures start from the posterior border and are discontinuous in front. Free cheeks large ; eyes crescentic, placed near the posterior border. Thorax with 10 segments, pleurae ridged. Pygidium very large, fan-shaped ; axis very short; lateral lobes large, with radiating grooves. Bala Beds to Devonian. Ex. B. Jtabellifer, Devonian. Phacops. Head-shield nearly semicircular ; glabella promi- nent, broadest in front, with 3 or 4 furrows, which are sometimes indistinct ; facial sutures commencing on the lateral borders of the cheeks in front of the genal angle, and continuous in front of the glabella. Eyes generally large, formed of large, distinct lenses. Thorax with 11 segments, pleurae grooved. Pygidium variable. Ordovician to Devonian. The species of Phacops are divided into a number of groups which should be regarded as sub-genera, or perhaps genera ; some of these are : — Phacops (restricted) : glabella inflated and expanded in front, with the two anterior furrows obscure. Eyes large. No genal spines. Ex. P. stokesi, Silurian. Trimerocephalus : glabella furrows obscure or absent. Eyes small. No genal spines. Ex. T. Icevis, Devonian. Acaste : glabella not much expanded in front, all the furrows distinct. Ex. A. doicningice, Silurian. Chasmops : glabella greatly expanded in front, two anterior furrows large, two posterior very small. With genal spines. Ex. C. conophthalmus, Bala Beds. Odontochile ( = Dalmanites) : glabella not much ex- panded, all the furrows distinct. Genal spines long. Pleurae often produced into spines. Ex. 0. caudatus, Silurian. 20—2 308 CRUSTACEA. TRILOBITA Cheirurus. Head-shield semicircular, genal angles pointed or with spines ; glabella convex, oblong or ovoid, with three pairs of furrows which are sometimes continuous across, the last pair uniting with the neck-furrow. Facial sutures continuous in front and ending on the external margins. Free cheeks small ; eyes promi- nent. Thorax with usually 11 segments, pleurae grooved, and produced into spines. Pygidium small, with 4 segments, lateral lobes with backwardly-directed spines. Tremadoc to Devonian. Ex. C. articulatus, Devonian ; C. bimucronattis, Bala to Ludlow Beds ; C. juvem's, Bala Beds. Deiphon. Glabella globular without furrows. Fixed cheeks forming two long curved spines. Thorax with 9 segments ; pleurae in the form of free spines. Pygidium short, prolonged into two spines on each side. Llandovery and Wenlock. Ex. D. forbesi. SphaereXOCllUS. Glabella large, spheroidal, with 3 pairs of furrows — the two anterior indistinct, the posterior curving back- wards and joining the deep neck-furrow. Cheeks small ; eyes small, near the axial furrow ; facial suture starts from the genal angle. Thorax with 10 segments ; pleurae without grooves, with rounded ends. Pygidium small, with 3 segments. Ordovician and Silurian. Ex. S. mirus, Wenlock Limestone. Staurocephalus. Glabella with a spherical lobe projecting in front of the cheeks ; the remainder of the glabella narrow and cylindrical with 2 pairs of furrows and a deep neck-furrow. Cheeks very convex, with a flat border. Facial suture starts from the lateral margin and cuts the front margin. Eyes on stalks. Thorax with 10 segments ; pleurae ridged, produced into spines. Pygidium small, of 4 segments, with pleurae produced into spines. Bala to Wenlock Limestone. Ex. S. mwchisoni, Wenlock Limestone. Encrinurus. Head-shield covered with tubercles ; with a flat border, and pointed genal angles ; glabella pyriform, confluent with the border in front, its furrows indistinct or absent ; eyes small, on short peduncles. Facial sutures continuous in front, ending just in front of the genal angles. Free cheeks narrow. Thorax with 11 similar segments, pleurae ridged. Pygidium narrow, triangular, with many segments in the axis, with 6 to 12 pleurae bent backwards and diverging from the axis. Bala to Upper Ludlow. Ex. E. punctatus, Wenlock Limestone. CRUSTACEA. TRILOBITA 309 Cybele. Similar to Encrinurus. Three pairs of more distinct glabella furrows ; border continuous in front of the glabella ; genal angles usually rounded; facial sutures continuous in front. Thorax with 12 segments ; pleurae of the first 5 with blunt ends, those of the remaining 7 produced into spines. Pygidium with 4 or 5 pleurae which bend sharply backwards and converge towards the axis. Ordovician. Ex. C. verrucosa, Bala Beds. Lichas. Test covered with tubercles. Head-shield convex, relatively small, with genal spines. Glabella broad, with a central raised part, furrows directed backwards. Facial sutures pass from the posterior to the anterior border. Cheeks and eyes small. Thorax with 9 or 10 segments ; pleurae grooved, ending in rather long spines. Pygidium large, showing 2 or 3 segments, lateral parts produced into spines. Llandeilo to Wenlock. Ex. L. cmglicus, "Wenlock. Fig. 133. Acidaspis prevosti, from the Silurian. Head-shield. (After Barrande.) 1, 2, 3, first, second, and third glabella furrows (the first usually indistinct) ; a, central part of the glabella ; c — b — n, inner furrow of glabella ; c — v, neck-furrow ; d — v — x, axial furrow ; Tc — .t, fixed cheek ; o, eye ; o — n, eye-line ; p, genal spines ; q, spines from neck-ring ; r, neck-ring ; s — s', facial suture ; y, spines. En- larged. Acidaspis (fig. 133). Head-shield broad, its trilobation not well marked, with genal spines, and usually with spines at the margin of the head; glabella with a pair of longitudinal furrows parallel to the axial furrows, and with two or three lateral furrows. Facial sutures start from the posterior margin just within the genal angle and cut the front margin. Free cheeks large. Eyes con- nected with the glabella by an eye-line. Thorax with 9 or 10 310 CRUSTACEA. TRILOBITA segments, pleurae with ridges produced into long spines. Pygidium small, with long spines. Llandeilo Beds to Devonian. Ex. A. barrandei, A. brighti, Wenlock. Phillipsia. Body oval ; glabella with nearly parallel sides, with 3 or 4 narrow lateral furrows, of which the posterior one curves backwards and joins the deep neck-furrow, thus cutting off a basal lobe. Facial sutures cut the posterior border obliquely, and the anterior border in front of the eye. Free cheeks large ; eyes large, reniform. Thorax with 9 segments, pleurae grooved. Py- gidium semicircular, with 12 to 18 segments, margin entire. De- vonian to Permian. Ex. P. derbiensis, Carboniferous. ProetUS. Closely allied to Phillipsia but with fewer segments in the pygidium. Ordovician to Carboniferous, chiefly Devonian. Ex. P.fletcheri, Wenlock. Griffithides. Body oval ; glabella with inflated basal lobes cut off by the posterior furrow, and without other lateral furrows ; main part of glabella pyriform ; eyes rather small. Thorax with 9 segments. Pygidium rounded, with about 13 segments. Car- boniferous Limestone. Ex. O. seminiferus. Distribution of the Trilobita The Trilobites are confined to the Palaeozoic period, and form one of the most important and striking features in the faunas of the Lower Palaeozoic deposits. They occur first in the Lower Cambrian Beds, and reach their maximum in the Ordovician. In the Silurian, Trilobites are still abundant, but become less important in the Devonian, and in the Carboniferous are represented by four genera only. In Europe they do not extend beyond the Carboniferous Limestone, but in North America one species of Phillipsia has been found in the Permian. Already in the Cambrian period the Trilobites were represented by a considerable variety of forms, showing that even then the group must have been of considerable CRUSTACEA. TRILOBITA 311 antiquity, but at present no traces of the ancestors of the Cambrian forms have been found. It is in the Cambrian System that we meet with the largest, as well as the smallest Trilobites, e.g. Paradoxides and Agnostus. As a whole, it may be said that the Trilobites which are con- fined to the Cambrian period are characterised by the possession of a large number of thoracic segments, and of a small pygidium (fig. 130) ; whereas, in the Ordovician, most of the characteristic genera have fewer segments in the thorax and possess large pygidia (fig. 132). Many of the Trilobites seem to have had a wide geographical distribution; for example, most of the genera which have been recognised in Australia occur also in Europe. Some, however, apparently had a more limited range; thus, for instance, Sao, Arethusina, and Ellipso- cephalus are very common in Bohemia, but are seldom found elsewhere. The most important genera found in the different systems are mentioned below ; those marked with an asterisk* occur only in one system. Cambrian. Agnostics, Microdiscus* ', Paradoxides*, Olenellus*, Sao*, Ellipsocephalus* , Concoryphe*, Olemcs*, Niobe, Angelina*. Ordovician. Agnostics, Ampyx, Trinucleus* , Ogygia, Asaphus, Illomics, JEglina*, Calymene, Cybele*, Lichas. Ogygia, Asaphics, Triniccleus and Ampyx are abundant. Silurian. Calymene, Homalonotics, Illamus, Phacops, Cheimcrus, Deiphon*, Sphwrexochus, Encrinurus, Acidaspis, Proetus, Lichas. Calymene and Phacops are particularly abundant. Devonian. Homalonotics, Bronteics, Phacops, Cheirurus, Proetics. Carboniferous. Phillipsia, Grij/ithides*, Brachymetopus*. 312 CEUSTACEA. BRANCHIOPODA SUB-CLASS II. BRANCHIOPODA The Branchiopoda include the water-fleas (Daphnia, etc.) and other forms. The body is more or less distinctly segmented, and often the greater part, or sometimes the whole, of it is covered by a carapace which may be shield- like, as in A pus, or in the form of a bivalved shell re- sembling a lamellibranch, as in Estheria (fig. 134) ; in some forms there is no carapace. The number of segments in the trunk (abdomen and thorax) varies very widely; in some cases there may be as many as 42 ; often the division of the trunk into thorax and abdomen is indistinct. On the head there are generally two pairs of antennae, one of mandibles, and one or two of maxillae. The trunk bears several pairs of swimming-feet, which are flattened and leaf-like, and their basal parts function as jaws (gnatho- bases). The abdomen may be without appendages, but generally appendages are present except on the posterior segments. The last segment of the abdomen (the telson) often bears a pair of spine-like or jointed processes forming a caudal fork. Compound eyes are usually present, and often also a simple unpaired eye ; the former are usually sessile, but in some cases are borne on movable stalks. The Branchiopoda are divided into two Orders, (1) the Phyllopoda, (2) the Cladocera; the latter are not definitely known as fossils. Estheria (fig. 134). Valves equal, thin, horny ; ovate, oblong or quadrilateral, united at the straight dorsal border ; the apices of the valves placed anteriorly, or nearly central. Surface generally covered with con- centric ridges or striae. Old Red Sand- „ . T . . . Jng. 134. Estheria minuta, stone to present day. Lives in fresh from the Trias x 3. or rarely in brackish water. Ex. E. minuta, Trias, etc. CRUSTACEA. OSTRACODA 313 Distribution of the Branchiopoda The Branchiopoda live mainly in fresh water, but some are found in the sea, in salt lakes, and in brackish water. Only a very few genera are found fossil ; Protocaris, which resembles Apus, occurs in the Lower Cambrian of North America. In the Upper Palaeozoic and later deposits a few genera are present, Estheria being common. Apus ranges from the Trias to the present day. SUB-CLASS III. OSTRACODA The Ostracods (fig. 135) are indistinctly segmented and generally of minute size. The body is usually com- pressed laterally, and is completely enclosed in a bivalved carapace, which may be horny or calcareous. One valve 2 — 7 Fig. 135. Lateral view of Cypris Candida. (After Zenker.) 1, antennules; 2, antenna? ; 3, mandibles ; 4, first maxillae ; 5, second maxillae ; 6, 7, first and second pairs of legs ; 8, tail ; 9, eye. Enlarged. is placed on each side of the animal, and the two valves are joined together dorsally by an elastic ligament which serves to open the shell ; sometimes a hinge is formed by means of interlocking teeth and ridges ; an adductor muscle passes from the interior of one valve to the other and by its contraction the shell is closed; usually the muscular impression can be seen from the outside. There 314 CRUSTACEA. OSTRACODA are seven pairs of appendages, which can be protruded when the shell is opened. In some of the marine forms the shell is notched anteriorly so as to allow the antennae to pass through when the shell is closed. The head carries two pairs of large antennae which are used for locomotion, one pair of mandibles, and two of maxillae. The thorax has two or three pairs of appendages, which are not leaf-like. The abdomen is rudimentary and is without appendages ; it terminates either in a fork or in a spiny plate. Respiration takes place by means of the general surface of the body. The carapace is in almost all cases the only part which occurs fossil; its surface may be smooth or variously ornamented. Leperditia. Carapace thick, smooth, convex, elongated, a little higher posteriorly. The right valve larger than the left. Hinge-line straight. There is a small tubercle (eye-spot) placed anteriorly near the hinge ; and posterior to it is a slightly elevated circular area. Cambrian to Carboniferous. Ex. L. kisinge?'i, Silu- rian ; L. okeni, Carboniferous. Primitia. Carapace generally equivalve, convex, oblong or ovate. Hinge-line straight. Each valve has a transverse groove which starts from the hinge-line. Cambrian to Carboniferous. Ex. P. strangulata, Bala Beds. B eyrie hi a (fig. 136). Carapace elongated, inflated, posterior border a little higher than the anterior ; dorsal border straight, ventral border semi- circular. Two or three large furrows pass from the dorsal towards the ventral edge ; the parts between the furrows are convex and often tuberculate, the middle part being the smallest. Cam- Fi°' ^ Beyrichiacom- . ~ .„ -r-i r. 7- phcata, Bala Beds. bnan to Carboniferous. Ex. B. complicata, ^he lower figure Llandeilo and Bala. shows the dorsal __ _. .I, aspect of the united Entomis. Carapace equivalve, al- valves, x 2. mond-shaped, with a deep transverse furrow which passes from the dorsal border (a little in front of the CRUSTACEA. OSTRACODA 315 middle) towards the ventral border. Surface generally striated. Anterior margin notched for the passage of the antenna?. Ordo- vician to Carboniferous. Ex. E. tuberosa, Silurian. Cy there. Shell oblong-ovate or subquadrate, highest in front ; smooth or ornamented with pits, spines, or ridges. Hinge with teeth anteriorly and posteriorly. Ordovician to present day (chiefly Cretaceous and later). Ex. C. striato-punctata, Eocene; C. punctata, Pliocene. Cypris (fig. 135). Carapace thin, smooth or punctate, kidney- shaped or oval ; ventral edge often concave. Left valve the larger. Hinge without teeth. Purbeck Beds to present day. Fresh water. Ex. C. faba, Miocene ; C. gibba, Oligocene to present day. Cypridea. Valves ovate-oblong, convex in the middle, broad at the anterior third, narrower behind ; with a notch at the anterior ventral angle behind a beak-like process. Surface smooth, punctate, or tuberculate. Hinge-margin straight, along the middle third of the dorsal edge. Left valve the larger. Purbeck, Wealden, and Oligocene. Fresh water. Ex. C. valdensis, Wealden Beds, etc. Distribution of the Ostracoda The Ostracods have a very wide distribution at the present day ; many forms are marine, and some are abundant in fresh water. The marine forms often occur in shoals ; some are pelagic, but others live on the sea- floor and are more abundant in shallow than in deep water, only fifty-two species being found beyond the 500 fathom line. The fossil forms are very numerous, the earliest occur- ring in the Cambrian. Leperditia, Primitia, and Beyrichia are abundant in the Lower Palaeozoic ; Entomis in the Devonian ; and Cypridina and Bairdia in the Carboni- ferous. Cypridea is common in the Purbeck and Wealden Beds ; and Cythere in the Tertiary formations. 316 CRUSTACEA. CIRRIPEDIA SUB-CLASS V. CIRRIPEDIA The Cirripedes include the barnacles, acorn-shells, etc. — forms which differ considerably in appearance from the other crusta- ceans and were for a long time re- garded as molluscs. The body is completely enclosed in a fold of the skin, which commonly secretes a calcareous shell. The animal, in the adult state, is fixed to a foreign object by the anterior end of the head, either directly or by means of a stalk or peduncle. The segmenta- tion of the body is indistinct. The head is not well marked off from the thorax ; it bears one or two pairs of antennae, one pair of man- dibles, and two pairs of maxillae. The thorax has usually six pairs of biramous feathery limbs. The abdomen is rudimentary and without appendages. Heart and vascular system are absent ; nearly all forms are hermaphrodite. The shell consists of several pieces ; in Lepas (which possesses a stalk) there are five, two are placed on each side of the body, those near the stalk being termed the scuta (fig. 137, a), those at the upper end the terga (b), and there is also one unpaired part placed dorsally, the carina (c). Balanus has no stalk ; its shell consists of a tube formed of six pieces, within which the scuta and terga are placed. Fig. 137. Lepas australis, Recent, a, scutum ; b, tergum; c, carina ; d, peduncle. Natural size. (After Darwin . ) CRUSTACEA. CIRRIPEDIA 317 Distribution of the Cirripedia The Cirripedes are all marine, and the greater number are found in shallow water, particularly near the coasts, Balanus being especially characteristic of littoral regions. At depths greater than 1000 fathoms, only two genera, Scalpellum and Verrucosa, have been found, and these are not confined to deep water. Cirripedes are rare in the Palaeozoic and early Mesozoic formations, but become moderately common in the Chalk, and are abundant in some of the later Tertiary deposits. A few examples, which are believed to be Cirripedes, have been found in the Cambrian of North America. In the Ordovician the genera Pollicipes, Scalpellum, and Turrilepas occur : the first two are represented in the Silurian and various later formations (especially the Chalk) ; the last ranges on to the Devonian. Loricula and Brachylepas are found in the Chalk. Balanus appears in the Eocene, and Lepas in the Pliocene. SUB-CLASS VI. MALACOSTRACA The Malacostraca are usually of larger size than the Crustacea belonging to the preceding groups. With the exception of the Leptostraca, the number of segments is constant, there being eight in the thorax, and seven in the abdomen (including the telson), making altogether twenty segments in the body. The abdomen is clearly marked off from the thorax by the character of the appendages. In some cases the development is direct, the young having the same or nearly the same form as the parent, but usually larval stages occur ; the principal 318 CRUSTACEA. MALACOSTRACA larval form is the zosea, but a nauplius stage may also occur. In many groups of the Malacostraca a dorsal shield or carapace is present, and usually coalesces with the terga of some or all of the thoracic segments, forming a cephalo- thoracic shield (fig. 143, a — c). The telson (e) — a median plate at the end of the abdomen — does not terminate in a caudal fork except in the Leptostraca. Each segment of the body, except the telson, usually carries a pair of appendages. The first pair of antennae (unlike those in the preceding groups) are biramous. In some divisions of the Malacostraca the thoracic appendages are all biramous ; but often, with the exception of some of the anterior appendages, they are uniramous, the exopodites being absent. One or more (often three) of the anterior appendages of the thorax are modified so as to function as jaws, and are known as maxillipedes ; the remainder of the thoracic appendages are used in locomotion. The appendages of the abdomen are biramous; the first five pairs are swimming legs (pleopods) ; the last pair (the uropods, fig. 143,/) are flattened and form with the telson a fan-like tail-fin. In the Malacostraca the position of the genital apertures is constant (p. 291). A pair of compound eyes are usually present. Calcareous ossicles are developed in the stomach forming a ' gastric mill.' There are nine Orders of the Malacostraca : — (1) Lepto- straca, (2) Syncarida, (3) Schizopoda, (4) Cumacea, (5) Tanaidacea, (6) Isopoda, (7) Amphipoda, (8) Stomato- poda, (9) Decapoda. The Cumacea and Tanaidacea are not known to occur fossil. CRUSTACEA. LEPTOSTRACA 319 ORDER I. LEPTOSTRACA (PHYLLOCARIDA) The Leptostraca differ in several respects from all the other Orders of the Malacostraca, and possess characters which connect them with the Phyllopoda. Only four genera are now living, of which the commonest is Nebalia; they are small shrimp-like Crustacea, with the body Fig. 138. Paranebalia longipes, Recent. (After Sars.) x 13. a, ros- trum ; b, eye ; c, antennule ; d, antenna ; e, mandibular palp ; /, last thoracic leg ; g, first abdominal leg ; h, k, rudimentary limbs of fifth and sixth abdominal segments ; I, caudal fork ; m, cephalic part of carapace ; ??, mandible ; o, second maxilla ; p, adductor muscle of carapace; q, first maxilla; r, first segment of thorax; s, ovary; t, last segment of thorax ; u, first abdominal segment. laterally compressed. A large bivalved carapace (fig. 138, m) covers the head, the thorax, and some of the abdominal segments, but is united to the head only ; the two valves are connected by an adductor muscle (p) just 320 CRUSTACEA. LEPTOSTRACA as is the case in the Ostracods and many Phyllopods. In front of the carapace is a movable plate or rostrum (a). There are twenty-one segments in the body — five in the head, eight in the thorax (r — t), eight in the abdomen (u — I), the last segment (or telson) carrying two pointed processes — the caudal fork (I). There are nineteen pairs of appendages, as in the Malacostraca : the head bears two pairs of antennae (c, d), one pair of mandibles (n), two of maxillae (q, o) ; on the thorax there are eight similar pairs of limbs (f) which are leaf-like and resemble those of Phyllopods ; the abdomen has six pairs of appendages, the first four being large biramous swimming legs (g), the last two small and uniramous (h, k). The two posterior segments are without appendages. The eyes are com- pound and stalked. The mandible bears a long, three- jointed palp (e). The anus opens on the telson between the two branches of the caudal fork. The Leptostraca agree with the Malacostraca in having the abdomen and its appendages clearly marked off from the thorax ; in the position of the genital apertures ; in possessing eight segments in the thorax ; in having nine- teen pairs of appendages ; and in the occurrence of a masticatory stomach. They differ from the Malacostraca in the bivalved carapace with an adductor muscle ; in the possession of leaf-like thoracic legs, and of eight abdominal segments with a caudal fork. From most of the Mala- costraca they are further distinguished by the presence of a movable rostrum, and by all the segments of the thorax being free. The group of the Malacostraca to which the Leptostraca seem to be most nearly allied is the Mysidae — a family of the Schizopoda. In the characters of the carapace and of the thoracic legs, and in the presence of a caudal fork? the Leptostraca CRUSTACEA. LEPTOSTRACA 321 resemble the Phyllopoda. But they differ from them in the clear separation of the thorax from the abdomen ; in the possession of a rostrum and a mandibular palp ; and in the long anterior antennae. Stalked eyes are found in some Phyllopoda and in many Malacostraca. The Leptostraca are clearly generalised types, and are probably to be regarded as the last survivors of a primitive group of Crustacea. The Order is, however, without representatives in post-Triassic rocks ; but a number of Crustacea which closely resemble the living Leptostraca in the form of the body, with in some cases a movable rostrum, are found in the Palaeozoic formations; they differ, however, in being much larger, and, usually, in the caudal fork consisting of more than two spine-like pro- cesses. The appendages of these Palaeozoic forms are almost unknown, and consequently it is difficult to deter- mine their affinities satisfactorily. Masticatory organs in the stomach are stated to occur in some of the fossil forms. Some of the principal Palaeozoic genera are described below. Hymenocaris (fig. 139). Carapace semi-oval, smooth, not bivalved. Abdomen formed of eight segments, and with four, five, or six caudal spines. Lingula Flags. Ex. H. vermicauda. Ceratiocaris. Carapace bi- valved, often marked with striae, oval, narrow in front, truncated behind and _. „„_ TT . .big. 139. Hymenocaris vermi- with a lanceolate rostrum in front. cauda, Lingula Flags. x£. Thorax and abdomen formed of four- teen or more segments, the first seven or more being covered by the carapace ; telson long and pointed, with two lateral spines. Tre- madoc Beds to Carboniferous. Ex. C. stygia, C. papilio, Ludlow Beds. w. p. 21 322 CRUSTACEA. LEPTOSTRACA Caryocaris (fig. 140). Carapace bivalved, pod-like, narrow smooth, rounded at one end (pro- bably the posterior), truncated at the other. Arenig Rocks. Ex. C. wrighti. Dithyrocaris. Carapace large, bivalved, with a narrow anterior notch ; rostrum unknown. Each valve semi-oval, truncated behind, with a median longitudinal ridge ; another ridge at the dorsal margin where the valves join. Surface often with pits or granules. Ex- Fig. 140. Caryocaris wrighti, Arenig Rocks. Natural size. The abdomen has not been found attached to the cara- pace as shown above ; some authors consider that the broad end of the carapace is anterior. posed part of abdomen short, with a narrow, sharply-pointed telson bearing on each side a spine-like appendage. Devonian and Carboniferous. Ex. D. colei, Carboni- ferous. Discinocaris. Carapace sub-circular, slightly convex, formed of one piece with a notch in front in which the triangular rostrum is placed. Surface with concentric linear ridges. Silurian. Ex. D. browniana, Llandovery. Aptychopsis. Similar to the last, but carapace divided into two parts by a median suture which starts from the rostral notch. Silurian. Ex. A. lap worthy Llandovery. Distribution of the Leptostraca The Leptostraca are all marine, and live mainly in shallow water or at moderate depths. In Britain the earliest representative is Hymenocaris, found in the Lingula Flags ; Ceratiocaris occurs in the Tremadoc Beds and ranges on to the Carboniferous, but is most abund- ant in the Silurian. Caryocaris is characteristic of the Arenig Rocks. Aptychopsis and Discinocaris occur in the CRUSTACEA. SCHIZOPODA 323 Silurian. Echinocaris is found in the Devonian ; and Dithyrocaris in the Carboniferous. One genus (Aspido- caris) has been recorded from the Trias. ORDER II. SYNC ARID A The Syncarida are a small group of primitive Mala- costraca, the living representatives of which are found in fresh water in Tasmania and Victoria, and belong to three genera of which the best known is Anaspides. The body is elongated and without a carapace, and is remarkable for the fact that all the thoracic segments are distinct. All the thoracic legs are similar in general character, and all, except the last one or two, are biramous ; their coxo- podites bear externally two rows of plate-like gills, but these have not been found in fossil specimens. The abdomen is large, and the first five pairs of appendages consist of long, many-jointed exopodites and small endo- podites ; the appendages of the sixth segment form with the telson a tailfin. Fossil representatives of the Syncarida are found in the Carboniferous and Permian deposits, and belong to the genera Prceanaspides, Palceocaj'is, Acanthotelson, and Uronectes (= Gampsonyx). These appear to be closely allied to Anaspides. ORDER III. SCHIZOPODA The Schizopods (fig. 141) are small Crustacea in which the thorax is more or less completely covered by a well- developed, but thin and usually flexible, cephalo-thoracic shield. The eight pairs of thoracic legs are generally biramous and, unlike those of the Decapods, are all similar 21—2 324 CRUSTACEA. SCHIZOPODA in character, with the exception that, in some forms, the first one or two pairs may serve as maxillipedes. The abdomen is long and slender; its five anterior pairs of appendages are biramous swimming legs, whilst the sixth pair form with the telson a tail fin. The compound eyes are stalked. Fig. 141. A Recent Schizopod — Nyctiphanes norvegica. (After Watase.) The black dots indicate the phosphorescent organs ; the gills are seen between the thoracic and the abdominal appendages. Slightly magnified. Recent work tends to show that the Schizopoda do not constitute a natural group, since of its two main divisions one appears to be related to the Pecapoda, whilst the other approaches more nearly the Cumacea, Isopoda, and Amphipoda. Since, however, the affinities of a number of fossil schizopod-like forms have not yet been satis- factorily determined, it will be convenient to retain for the present the group Schizopoda. Living Schizopods, with the exception of a species of Mysis, are marine, and many of them are pelagic. The fossil forms which have been referred to this group are found mainly in the Carboniferous rocks, especially in the CRUSTACEA. ISOPODA 325 south of Scotland where they are sometimes numerous ; the principal genera are Pygocephalus, Crangopsis, An- thrapakemon, and Tealliocaris. In the Upper Devonian Pakeopalcemon is found, and may belong to this group. ORDER VI. ISOPODA In the Isopods the body is usually flattened dorso- ventrally. There is no cephalo-thoracic shield, but the first thoracic segment (occasionally also the second) is fused with the head. The eyes are sessile. The first pair of thoracic appendages are maxillipedes, the other seven are p.g ^ Arch(Eonis, walking legs. The abdomen is often ens brodiei, from short, and some or all of its segments Slightly reduced. are fused together and with the telson. Some of the abdominal appendages function as gills. Many Isopods are marine, but some are found in fresh water, whilst a few live on land (e.g. the wood-louse, Oniscus ctsellus). Many forms are parasitic, and infest fish and Crustacea. Fossil Isopods are rare. Oxyuropoda, from the Old Red Sandstone of Kiltorcan (Ireland), is probably an Isopod; and an imperfect specimen, from the Old Red Sandstone of Hertfordshire, described under the name of Prcearcturus gig as, perhaps belongs to this group. Arthro- plemxi, from the Coal Measures, has been referred to the Isopoda. Undoubted examples of this Order are found in Jurassic and later formations : Cy do splicer oma in the Great Oolite and Purbeckian ; Archceoniscus in the Pur- 326 CRUSTACEA. AMPHIPODA beckian (fig. 142) ; Palcega in the Cambridge Greensand, the Lower Chalk, and foreign Tertiary ; and Eosphceroma in the Oligocene of the Isle of Wight. ORDER VII. AMPHIPODA The Amphipods {e.g. Gammarus, Talitrus) are usually of small size, and generally the body is compressed from side to side. Just as in the Isopods, there is no cephalo- thoracic shield, and the first thoracic segment (sometimes also the second) fuses with the head. The first pair of thoracic appendages are maxillipedes ; the appendages of the seven free segments bear the gills, and are divisible into an anterior group of four in which the terminal parts of the legs are directed backwards, and a posterior group of three in which the terminal parts are directed forward. The abdomen is usually elongated and carries six pairs of appendages ; the three anterior serve for swimming, the three posterior for jumping. The eyes are sessile. Some of the Amphipods are marine, others live in fresh water. The marine forms have a wide distribution, and are very numerous, especially in shallow water, and in Arctic and Antarctic seas. Fossil Amphipods are very rare. Necrogammarus from the Lower Ludlow rocks of Leintwardine has been referred to this group, but its systematic position is uncertain — Peach thinks that it may belong to the Myriapoda. Other forms, whose affinities are likewise uncertain, have been recorded from the Carboniferous and Permian ■ de- posits. Undoubted Amphipods are found in the Tertiary formations and belong mainly to genera which are still existing (e.g. Gammarus from the Miocene). CRUSTACEA. STOMATOPODA 327 ORDER VIII. STOMATOPODA In the Stomatopocls the body is long, and flattened dorso-ventrally ; the cephalo-thoracic shield is short and does not cover the four posterior thoracic segments. At the front of the head there are two, small, movable seg- ments which are not covered by the shield ; the first bears the stalked eyes, the second bears the antennules. A rostral plate is articulated to the front of the cephalo- thoracic shield. The five anterior pairs of thoracic append- ages are directed forwards as maxillipedes ; the three posterior pairs are slender biramous legs and are directed downwards. The abdomen is much larger than the an- terior portion of the body ; its five anterior appendages bear gills, and the sixth pair form with the broad telson a strong tail fin. Squilla is the best known genus of this Order. All the forms are marine and live in shallow water. The Stomatopods are very rare as fossils. A few Crustacea found in the Carboniferous (e.g. Necroscylla) have been referred to this group ; but undoubted representatives, belonging to the genus Sculda, occur in the Solenhofen Limestone (Upper Jurassic). Squilla has been found in the Chalk of Lebanon and in some of the Eocene forma- tions (London Clay, etc.). ORDER IX. DECAPODA The Decapoda include lobsters (fig. 143), cray-fishes, crabs, etc. The cephalo-thoracic shield (a — c) is large and well developed, and usually covers all the segments of the thorax (b — c) ; frequently it is marked out into an 328 CRUSTACEA. DECAPODA anterior and a posterior portion by a groove, — the cervical sutiwe (b). The shield is often produced in front into a rostrum (a). The gills are connected with the thoracic appendages and segments, and are placed in a chamber formed by the downward prolongation of the cephalo- thoracic shield. The appendages on the head are (1) an- tennules, (2) antennae, (3) mandibles, (4, 5) maxillae ; the last three pairs serve as jaws. On the thorax the first three pairs of limbs are modified as maxillipedes ; the posterior five pairs (k — 6) are the ambulatory limbs, P Fig. 143. Glyphea regleijana, Oxfordian. a — c, cephalothorax ; a — 6, head; b — c, thorax ; a, rostrum; c — e, abdomen; d, sixth abdominal segment ; e, telson ; /, appendage of sixth abdominal segment ; g, eye ; h—o, appendages of cephalothorax ; k — o, ambulatory limbs. X -j. which, in most cases, are uniramous ; they consist of seven joints, and, as a rule, some of them terminate in pincers or chelce. The name ' Decapoda ' is taken from these five pairs of ambulatory limbs. The abdomen bears six, or fewer, pairs of small appendages. The eyes are compound and stalked. The Decapoda may be divided into three sections : — (1) Macrura, (2) Brachyura, (3) Anomura. The last section includes the hermit-crabs and hermit-lobsters and is represented by only a few fossil forms. CRUSTACEA. DECAPODA 329 Section 1. Macrura This section includes the lobsters, shrimps, and cray- fishes. The abdomen (fig. 143, c — e) is long, well deve- loped, and ends in a large tail fin (e,f) formed by the telson and the appendages of the sixth abdominal segment. JEger. Body laterally compressed. Abdomen long. Rostrum long, with small tubercles. Antennules nearly as stout, but not so long as the antennas. Last maxillipedes long, with chelae. Third pair of ambulatory legs longer than the others ; the fourth and fifth pairs slender and flattened, without chelae. Trias and Jurassic. Ex. JE. tipularius, Solenhofen Limestone (Upper Jurassic). Eryon. Cephalothorax flattened, broader than long, with a median dorsal ridge on the posterior part ; the lateral margins usually dentate, and at the anterior third are deep notches. Rostrum short. The first four pairs of ambulatory limbs on the thorax bear chelae, the anterior pair being larger than the others. Abdomen of about the same length as the cephalothorax ; the first segment very short. Telson trigonal. Trias to Cretaceous. Ex. E. antiquus, Lias ; E. propinquus, Solenhofen Limestone. Grlyphea (fig. 143). Cephalothorax ornamented with granules ; rostrum short. In front of the cervical suture are several spiny or tuberculate parallel ridges which extend towards the anterior margin. Posterior to the cervical suture are generally two other grooves. The anterior pair of ambulatory limbs are much longer than the others ; all are without chelae. Abdomen long. Trias to Cretaceous. Ex. G. regleyana, Oxfordian ; G. tenuis, Solenhofen Limestone (Upper Jurassic). Meyeria. Cephalothorax laterally compressed, with a sharp rostrum, and a deep V-shaped cervical suture ; with sharp, serrate, longitudinal ridges on the dorsal surface ; the sides of the cephalo- thorax covered with sharp granules. Abdomen semi-cylindrical, longer than the cephalothorax, and ornamented with longitudinal rows of granules. Lower Cretaceous. Ex. M. magna. 330 CRUSTACEA. DECAPODA Eryma. Body cylindrical. Cephalothorax covered with granules, with a median dorsal groove, a deep cervical suture, and a pointed rostrum. Behind the cervical suture are two nearly parallel grooves which unite at the sides. The three anterior pairs of ambulatory limbs with chelee, the first pair being very large, the others small. Telson undivided. Lias to Upper Jurassic. Ex. E. leptodactylina, Solenhofen Limestone ; E. elegans, Great Oolite, etc. Enoploclytia. Body large, long, narrow ; surface roughened with granules and tubercles. Cephalothorax elevated, narrowing in front, with a long rostrum. Behind the deep cervical suture are one or two nearly parallel furrows, from which lateral branches pass to the cervical suture. First pair of ambulatory legs very strong, with large chelee having teeth on the inside of the fixed part ; second and third pairs of legs slender, also with chelae. Telson large, subtrigonal. Upper Cretaceous. Ex. E. leachi, Chalk. Hoploparia. Body elongate, slightly compressed laterally. Cephalothorax covered with fine granules. Rostrum very narrow, long, sharp and not dentate. Cervical suture deep, not reaching the margins of the carapace ; in front of the cervical suture is a X-shaped groove. The two anterior pairs of ambulatory limbs very long, provided with large chelae. Abdomen sub-cylindrical. Lower Cretaceous to Eocene. Ex. H. longimana, Lower Greensand. Section 2. Brachyura This section includes the crabs. The abdomen is short and small ; it is bent up underneath the thorax, and bears from one to four pairs of appendages, but is without a tail fin. The cephalothorax is broad. Dromia. Cephalothorax oval or rounded, very convex, with the entire surface punctate ; anterior part with pointed elevations, posterior third with irregular ridges ; divided into regions by two transverse grooves. Rostrum short, triangular. Orbital notches (in which the eyes rest) are very deep. First pair of ambulatory legs CRUSTACEA. DECAPODA 331 strong, with large chelae ; second and third pairs short ; fourth and fifth slender. Abdomen of six segments and a telson in both sexes. Eocene to present day. Ex. D. lamarcki, London Clay. Palaeocorystes. Cephalothorax much longer than broad, tapering posteriorly, anterior border not dentate ; rostrum short. Orbital notches large with two small fissures. Cervical suture well defined. The five anterior segments of the abdomen short, the sixth quadrangular. Gault and Eocene. Ex. P. stokesi, Gault. Eucorystes. Cephalothorax trapezoidal ; anterior part with tortuous, band-like elevations ; posterior part smooth or finely granular. Cambridge Greensand. Ex. E. carteri. Necrocarcinus. Cephalothorax rounded, separated into regions by distinct grooves, ornamented with a few prominent tubercles. Eostrum triangular. Orbital notches rounded, open above, with two small fissures. Gault to Chalk. Ex. N. bechei, Cambridge Greensand. Xanthopsis. Cephalothorax rounded, convex, surface punc- tate, the posterior portion with rounded elevations ; the frontal border with four, and the anterior laterals with one to three, tooth- like processes. Orbital notches deep, without fissures. Chelae unequal. Abdomen of the male narrow and formed of four seg- ments and a telson. Abdomen of female broad, composed of six segments and a telson. Eocene. Ex. X. leachi, London Clay. Distribution of the Decajwda Most of the Decapoda are marine, the larger number living in shallow water; amongst those which inhabit deep water are representatives of the Eryonidse — a family which flourished in Jurassic times. Some groups of the Macrura and Brachyura live in fresh water, whilst some of the Anomura and Brachyura are terrestrial. No undoubted examples of the Decapoda are known to occur in Palaeozoic deposits ; but representatives be- 332 CRUSTACEA. DECAPODA longing to the section Macrura (e.g. Pemphix), appear in the Trias. The Macrura become abundant in the Jurassic, where, amongst others, the genera Glyphea, Eryon, Mecochirus, uEger, and Eryma are found. In the Cretaceous, Enoploclytia, Hoploparia and Meyeria occur. Podocrates is found in the Eocene, and Propalwmon in the Oligocene deposits. The first undoubted examples of the Brachyura are found in the Jurassic rocks, but only two or three genera are represented, of which Prosopon appears first in the Inferior Oolite and survives until the Lower Cretaceous, whilst Palceinachus is found only in the Forest Marble. In the Cretaceous the Brachyura become more abundant and are represented by Palceocorystes, Eucorystes, Ne- crocarcinus and several other genera. In the Eocene numerous forms occur, Xanthopsis and Dromia being common. The Brachyura attain their maximum at the present day. CLASS III. MYRIAPODA The Myriapoda include the millipedes, centipedes, and allied forms. The body consists of a distinctly-marked head, followed by segments which are usually numerous and similar in form, so that, externally, the limits of the thorax and abdomen cannot be defined. The head bears one pair of antennse ; and also mandibles and maxillae. The segments behind the head (except the last) bear in some cases one, in others two, pairs of legs each ; in the latter the segments are really double. The Myriapods breathe by means of trachea?. In the fossil state Myriapods are rare. The two principal Orders are : — (1) the Chilopoda, or centipedes, MYRIAPODA 333 (2) the Diplopoda, or millipedes. The first undoubted representatives of the Chilopoda occur in the amber found in the Oligocene Beds of Prussia; the Diplopoda have also been found mainly in this amber, but one form, which perhaps belongs to this Order, was discovered in the Cretaceous rocks of Greenland. The Palaeozoic Myriapods differ considerably from the later representatives of the group and are regarded by Scudder as constituting two distinct Orders which are confined to the Palaeozoic formations. The earliest examples are found in the Upper Silurian of Lanarkshire and belong to the genus Ar chides mas. In the Old Red Sandstone of Scotland Kampecaris and ArcJiidesmus occur. A larger number of forms (Xylobius, Euphoberia, Pattonia, Anthracodesmas) are found in the Carboniferous and Permian rocks. CLASS IV. INSECTA The body of an insect can be separated into head, thorax, and abdomen. The head is formed of fused segments ; it bears four pairs of appendages — one pair of antennae, one of mandibles, and two of maxillae. In the thorax there are three segments, each bearing one pair of legs ; the second and third segments usually carry a pair of wings on their dorsal surfaces. The abdomen is composed of several (commonly ten) segments, and is usually without appendages. Insects breathe by means of tracheae. No undoubted Insects are at present known from the Devonian or earlier formations. But in the Coal Measures and in the Permian the group is represented by a con- siderable variety of forms. Remains of insects have been 334 INSECTA found at many horizons in the Mesozoic and Cainozoic formations ; in England they are not uncommon in the Lias, the Stonesfield Slate, the Purbeck, the Wealden, and the Bembridge Beds. They are well represented in the Solenhofen Limestone (Upper Jurassic) of Bavaria, in the Miocene of Oeningen in Switzerland, and of Florissant in Colorado, and in the amber from the Oligocene Beds of Prussia. The Insects found in the Palaeozoic formations appear to be more generalised than the later forms, and the majority are referred by Handlirsch to Orders distinct from those found in Mesozoic and later periods. Only one Order, the Orthoptera, seems to have survived from Palaeozoic to later times. One of the extinct Orders — the PalaeOdictyoptera, is regarded as the ancestral stock from which the other Palaeozoic Orders originated, and the latter are considered to be connecting links between the Palaeodictyoptera and modern insect groups. Brongniart, however, believes that the Carboniferous insects can all be placed in the Orders adopted for existing forms, but that in Palaeozoic times the Orders were less sharply separated than at the present day. The Insecta include an enormous number of forms, and the specimens found fossil are often imperfectly pre- served, so that nothing more than a brief sketch of the distribution of the chief groups can be attempted here. ORDER I. APTERA The fossil examples of this Order (which contains small wingless insects) are found mainly in amber from the Oligocene of Prussia, and include several species of Lepisma, the silver-fish. INSECTA 335 ORDER II. ORTHOPTERA This Order is represented in the Coal Measures. Examples of the Forficuliclse (earwigs) have been found in the Oligocene amber and in the Miocene, but they are not common. Blattidse (cockroaches) are found in the Per- mian and are fairly common in the Jurassic ; the Tertiary forms occur mainly in the Oligocene amber. The Man- tidae (' soothsayers ') are found in the Oligocene ; the Phasmidse (leaf and stick insects) in the Upper Jurassic and Tertiary deposits. The Locustidae (locusts) are repre- sented in the Lias, in the Upper Jurassic of Solenhofen, and in the Miocene of Oeningen. The Gryllidae (crickets) occur in the Lias and in the Oligocene amber. ORDER III. NEUROPTERA Insects allied to the Neuroptera are met with in the Coal Measures, but the earliest forms which can be definitely referred to this Order occur in the Lias. Many examples of the Termitidae (white ants) have been discovered in the Oligocene and Miocene. The Odonata (dragonflies) are represented in the Lias, the Stonesfield Slate, the Solen- hofen Limestone, and in the Miocene of Oeningen and Colorado. Ephemeridas (may-flies) occur in the Oligocene amber and in the Miocene of Colorado. Panorpidae (scorpion-flies) appear in the Lias. Examples of the Phryganeidae (caddis-flies) are found in the Lias, the Pur- beck Beds, and in the Oligocene amber. ORDER IV. LEPIDOPTERA Butterflies and moths are very rare as fossils. A few occur in the Middle and Upper Jurassic rocks, e.g. Palceon- 336 INSECTA Una oolitica from the Stonesfield Slate. The Order is better represented, although still uncommon, in the Ter- tiary Beds ; examples have been found in the Oligocene of the Isle of Wight, the Oligocene amber of the Baltic, and in the Miocene of Colorado. ORDER V. COLEOPTERA. The Coleoptera (beetles) first appear in the Trias; they are more numerous in the Jurassic, and are well represented in some of the Tertiary Beds. Examples have been found in the Lias, the Stonesfield Slate, the Solenhofen Limestone, the Purbeck Beds, the Lower Chalk of Bohemia, the Oligocene amber, and in the Miocene of Oeningen and Colorado. ORDER VI. HEMIPTERA Insects allied to the Hemiptera are found in the Upper Palaeozoic rocks. Forms which can be definitely assigned to this Order appear in the Lias. Examples of the Aphidas (plant-lice) occur in the Oligocene and Miocene. Fulgoridse are found in the Lias, the Purbeck Beds, and in the Tertiary. Notonectidse (water-bugs) appear in the Upper Jurassic rocks, and are also found in the Oligocene and Miocene. ORDER VII. DIPTERA The Diptera include flies, fleas, gnats, and mosquitoes. A few forms are found in the Lias, the Solenhofen Lime- stone, and the Purbeck Beds ; the Order is represented by numerous forms in the Oligocene amber. ARACHNIDA 337 ORDER VIII. HYMENOPTERA This Order includes the ants, bees, and wasps. A few examples have been found in the Solenhofen Limestone and the Purbeck Beds ; a larger number are met with in the Oligocene amber, and in the Miocene of Oeningen and Colorado. CLASS V. ARACHNIDA Scorpions, spiders, and mites are common forms of the Arachnida. In the members of this Class the anterior segments of the body are fused together, forming a prosoma or cephalothorax which is covered by a carapace. This region usually bears six pairs of appendages, of which one pair is in front of the mouth. Antennae are absent, and no pair of appendages is modified to serve exclusively as jaws. The first and second pairs, known as chelicerce and pedipalpi, serve partly as jaws ; the four remaining pairs are long limbs, placed near the mouth, and used for locomotion and to some extent as jaws. The abdomen may or may not be segmented; in some groups it is divided into an anterior and a posterior region (mesosoma and metasoma), each of which consists typically of six segments. The first segment of the mesosoma bears the genital pore. The metasoma bears no appendages, and those on the mesosoma are never in the form of loco- motory limbs, but are connected with respiration ; in the primitive aquatic arachnids they are plate-like and bear lamellar gills ; in the terrestrial forms the gills are re- placed by lung-books or by tracheae. The Arachnida are divided into two sub-classes : — (1) Merostomata, (2) Euarachnida. w. p. 22 338 ARACHNIDA. MEROSTOMATA SUB-CLASS I. MEROSTOMATA The Merostomata are aquatic Arachnids which breathe by means of gills borne on the plate-like appendages of the mesosoma. There are two Orders: — (1) Xiphosura, (2) Eurypterida. ORDER I. XIPHOSURA The only living representative of the Xiphosura is the king-crab, Limulus (figs. 144, 145), found on the eastern shores of North America and Asia, and in the Malay Archipelago and the Indian Ocean. The body of Limulus is covered by a chitinous exoskeleton, and consists of a Fig. 144. Limulus polyphemus, Recent. Ventral surface. A, cephalo- thorax or prosoma. B, abdomen. C, portion of the tail-spine. 1 — 6, appendages of the prosoma; 1, chelicera; 2, pedipalp ; 3—6, ambulatory legs ; behind the mouth are the small chilaria ; 7 — 12, appendages of the abdomen ; 7, operculum ; 8 — 12, lamellar append- ages bearing gills, m, mouth. Reduced. ARACHNIDA. XIPHOSURA 339 prosoma or cephalothorax (fig. 144 A) and an abdomen (B) formed of the mesosoma and metasoma fused together. At the end of the abdomen is a long, movable tail- spine (C). Fig. 145. Limulus polyphemus, Recent. Dorsal view. 1, carapace covering prosorna (cephalothorax) ; 2, abdominal shield ; 3, tail- spine ; 4, median eye ; 5, lateral eye. (From Shipley and MacBride.) 22—2 340 ARACHNIDA. XIPHOSURA The prosoma or cephalothorax is covered dorsally by a large crescentic or nearly semicircular carapace (fig. 145, l), which is very convex above and carries on its upper sur- face two pairs of eyes, one compound and lateral (5), the other simple and median (4). The large compound eyes are near the middle of the lateral parts of the cephalo- thorax ; the small simple eyes are close together in the middle line, near the anterior margin. The abdomen is more or less hexagonal in outline and is movably articu- lated with the cephalothorax ; both have two longitudinal furrows on the dorsal surface, dividing a narrow axial part from a broad lateral portion on each side, thus giving a superficial resemblance to a Trilobite. The mesosoma forms the main part of the abdomen and is composed of six fused segments, the segmentation being shown by grooves on the dorsal surface, and by the six movable spines borne on each side. The small posterior part of the abdomen without grooves represents the metasoma. The prosoma (cephalothorax) carries six pairs of ap- pendages concealed in the concavity of its under surface ; the anterior pair (fig. 144, 1) (chelicerce) only are in front of the mouth and are small, three-jointed appendages with chelae. The other five pairs (2 — 6) are the long, six- jointed walking-legs and are placed at the sides of and just behind the mouth ; most of them (except the last pair) end in chelae, and their basal joints (except in the sixth pair) are spinose and function in mastication. Be- hind the mouth are a pair of small unjoin ted processes, the chilaria, which represent a seventh pair of append- ages. The abdomen carries six pairs of plate-like appendages ; the anterior pair are united, forming what is known as the genital operculum (7), on the posterior surface of which are the genital openings. The operculum ARACHNIDA. XIPHOSURA 341 covers the remaining five pairs of appendages, which are not united in the middle, and bear on their posterior faces the leaf-like gills, of which there may be from 150 to 200 on each appendage superposed like the leaves in a book. From the account given above it will be seen that Limulus resembles the scorpions in several respects. In both, the prosoma consists of at least six fused segments, covered dorsally by a carapace which bears a pair of median eyes and a pair of compound eyes. The meso- soma of Limulus differs from that of the scorpions in having the segments fused, and the metasoma of the former is much reduced ; but in both there is a tail-spine behind the anus. The prosoma bears six pairs of append- ages which, in both cases, are similar in form and position. On the mesosoma the genital operculum forms the first pair of appendages; the second pair are the pectines of the scorpions, and the first pair of plates which bear gills in Limulus. The next four segments carry lung-books in the scorpions and gill-books in Limulus. From these characters, and from the absence of antennae, it is concluded that Limulus is allied to the Scorpionida rather than to the Crustacea as was formerly supposed. The differences between the mesosoma and metasoma of Limulus and the scorpions are, to some extent, bridged over by some of the Palaeozoic Xiphosura described below. Limulus appears first in the Trias ; it has been found in the Middle Jurassic of Northampton, and is common in the Upper Jurassic of Solenhofen in Bavaria, and is also represented in the Upper Cretaceous and the Oligocene. In the Palaeozoic deposits — from Silurian to Permian — several other Xiphosura occur ; most of these differ from Limulus in having some or all of the abdominal segments 342 ARACHNIDA. XIPHOSURA free, and in some cases the abdomen is clearly separable into mesosoma and metasoma (fig. 146). In these respects the Palaeozoic Xiphosura approach both the Eurypterida and the Scorpionida more nearly than does Limulus. In most of the Palaeozoic specimens the append- ages are not preserved. The examples found in the Coal Fi8- 146- Semiaspis limu- loides, from the Lower Measures may perhaps have lived Ludlow Beds. x£. in fresh water. Belinurus. Form similar to Limulus. Prosoma semicircular, with a flat border and long spines from the posterior angles ; median part raised, with compound eyes at the sides and median eyes at the front. Mesosoma of five free segments, with the lateral parts produced into spines. Metasoma small, formed of three fused seg- ments with a long tail-spine. Coal Measures. Ex. B. regince. Prestwichia ( = Euproops). Prosoma similar to Belinurus. Abdominal segments (probably seven) fused, with a flat marginal part produced into spines, and a short tail-spine. Upper Devonian, Coal Measures, and Permian. Ex. P. rotundata, Coal Measures. Hemiaspis (fig. 146). Prosoma semicircular, with spines at the external margin and angles ; central part raised. Mesosoma of six broad, short, free segments ; metasoma much narrower, of three segments and a pointed tail-spine. Silurian. Ex. H. limuloides. Bunodes. Similar to Hemiaspis. Prosoma without spines. Mesosoma with broad axial part. Metasoma of three or four seg- ments. Silurian. Ex. B. lunula. Neolimulus. Prosoma very broad, rounded in front, with spinose angles; with median eyes and compound lateral eyes. Abdomen with eight or more free segments. Silurian. Ex. N. falcatus. ARACHNIDA. EURYPTERIDA 343 Distribution of the Xiphosura Fossil Xiphosura are rare, except in the Solenhofen Limestone (Upper Jurassic). The chief genera are : Silurian1. Hemiaspis, Neolimulus, Bunodes, Pseudoniscus. Devonian. Protolimulus, Prestwichia. Carboniferous. Belinurus, Prestwichia. Permian. Prestwichia in North America. Trias to Oligocene and Recent. Limidus. ORDER II. EURYPTERIDA The Eurypterids are found only in the Palaeozoic rocks and are remarkable for the large size which they often attain ; one form (Pterygotus anglicus) reaches a length of six feet and is the largest Arthropod known. The Eury- pterids have a scorpion-like appearance ; but, unlike the scorpions, they were all aquatic animals, and, with the possible exception of forms found in the Coal Measures, all marine. The body is compressed dorso-ventrally, and is protected by a chitinous exoskeleton (fig. 147) which is covered with small scale-like markings. The prosoma or cephalothorax consists of the six anterior segments fused together, and is usually quadrate or semicircular in outline. The carapace, which covers the dorsal surface of the prosoma, bears a pair of small, simple eyes near its centre (fig. 147, e), and a pair of large, lateral eyes — one at each of the outer front margins or at some little distance from those margins (d). 1 Aglaspis, from the Cambrian of Wisconsin, is perhaps referable to the Xiphosura. 344 ARACHNIDA. EURYPTERIDA Behind the prosoma come the twelve free and movable segments of the abdomen ; in Pterygotus (fig. 147) these ^ ^^~s&~^d- Fig. 147. Dorsal surface of Pterygotus osiliensis, from the Upper Silurian, Rootzikiill. c, first pair of appendages (chelicerse) ; d, com- pound eyes; e, simple eyes; g, tail-plate or 'telson'; 5', sixth pair of appendages of prosoma ; 1 — 6, segments of the mesosoma ; 7 — 12, segments of the metasoma. Reduced. (After Schmidt.) segments gradually decrease in width in passing from the anterior to the posterior end, but in many cases (fig. 149) ARACHNIDA. EURYPTERIDA 345 they are divisible into two groups — the anterior segments being short and broad, whilst the posterior are long and Fig. 148. Ventral surface of Pterygotus osiliensis, from the Upper Silurian, Rootzikiill. a, epistome ; b, metastoma ; c, first pair of appendages (chelicerae) ; d, compound eyes ; /, I., genital oper- culum ; g, tail-plate or ' telson ' ; V — 5', second to sixth pairs of appendages ; I. — V., ventral plate-like appendages of the mesosoma ; 7 — 12, segments of the metasoma. Reduced. (After Schmidt.) narrow. The six anterior segments of the abdomen bear appendages and form the mesosoma (fig. 148, I. — v. ; fig. 346 AEACHNIDA. EURYPTERIDA 149, vii. — xii.) ; the six posterior segments are without appendages and form the metasoma (fig. 148, 7 — 12 ; fig. 149, xni. — xviii.), at the end of which is the tail-plate or spine (g) ; this is sometimes {Eurypterus) spine-like, but usually in the form of an oval plate which may be pro- duced into a median spine as in Slimonia, or divided at the end as in some species of Pterygotus. Each segment of the prosoma is covered by a broad, slightly convex dorsal shield (or tergum), and by a ventral cuticle (or sternum), and the tergum of each segment overlaps the one next behind. In the metasoma each segment is surrounded by a continuous chitinous sheath. The mouth is on the under surface of the prosoma (fig. 149). In front of the mouth there is one pair of appendages only (i.), which end in chelae and are usually small. The other five pairs of appendages (n. — VI.) are at the sides of the elongate mouth ; they consist of from six to eight joints each, and are not chelate ; they functioned in locomotion, and also in mastication since the inner margins of the basal joints (or coxae) are provided with tooth-like processes ; the posterior pair (vi.), except in Stylonurus, are much larger than the others and have a very large basal joint. Placed just behind the mouth, in the median line, is an oval or heart-shaped plate, the metastoma (b), which covers the inner parts of the basal joints of the sixth pair of appendages. The metastoma represents the pair of chilaria of Limulus (p. 340), and the presence in some cases of a notch in front, and a median longitudinal groove on the surface, supports the view that the metastoma originated from a paired structure. Immediately in front of the mouth another plate, the epistoma, is found in Pterygotus (fig. 148, a). ARACHNIDA. EURYPTERIDA 347 The six segments of the mesosoma bear on the ventral surface five pairs of plate-like appendages (fig. 148, 1. — v.; fig. 149, VII. — xii.), each of which overlaps the one behind like the tiles on a roof, and on the posterior (or inner) surface of which are the leaf-like gills (fig. 149, c). The first pair of plates form the genital operculum, and are divided in the middle by a median process, which often extends beyond the posterior margin of the operculum on to the next pair of appendages ; the shape and size of the median process differ in the two sexes. The genital operculum covers the ventral surfaces of both the first and second segments of the mesosoma (fig. 149, vn., viii.). The segments of the metasoma (figs. 148, 7 — 12; 149, xiv. — xviii.) are protected by continuous chitinous rings and bear no appendages. In many respects the Eurypterids resemble the Scorpions. The number of segments in each of the three regions of the body is the same, and the two pairs of eyes are similar in character and position. In both Eury- pterids and Scorpions the prosoma bears six pairs of appendages, of which the first are pre-oral and chelate, and the remaining five agree in position and in general form ; but in the Eurypterids the number of joints in the walking legs varies, and the basal segments of all serve as jaws, whereas in the Scorpions the last two pairs function only in locomotion; also in the Eurypterids the last leg and the genital operculum are much larger relatively than in the Scorpions. One of the characteristic features of the Eurypterids is the large metastoma; this is repre- sented by the small sternum of the Scorpions. The pectines are absent in the Eurypterids, except in Glypto- scorpius from the Carboniferous — and this form should probably be regarded as a specialised offshoot from, rather 348 ARACHNIDA. EURYPTERIDA than an actual member of, the Eurypterida. The lung- books of the Scorpions are represented by the leaf-like gills of the Eurypterids, but the plate-like appendages of the mesosoma are absent in the Scorpions. In both groups the segments of the metasoma are free and without appendages and at the posterior end is a tail-spine. The differences between the Eurypterids and recent Scorpions are to some extent bridged over by Palceophonus, sl Silurian Scorpion (see p. 353). The Eurypterids agree in many respects with Limulus. The principal points of difference are : — (1) only the first pair of appendages are chelate in Eurypterids, whereas in Limulus all the walking-legs except the last, and the first in the male, may be chelate ; (2) the last pair of legs are larger in Eurypterids than in Limulus and their basal joints assist in mastication; (3) the large, single plate forming the metastoma in Eurypterids is represented by the pair of small chilaria of Limulus ; (4) the second seg- ment of the mesosoma in Eurypterids is without append- ages and is covered by the genital operculum; (5) in the abdomen all the segments are free in Eurypterids but fused in Limulus, and in the latter the metasoma is much reduced — these differences in the abdomen, however, are bridged over by the Palaeozoic Xiphosura. Eurypterus. Prosoma (cephalothorax) quadrate, the an- terior angles rounded ; the compound eyes are a little in front of the median lateral point on each side. The tail-spine is long, narrow, and pointed. The pre-oral appendages are small and con- sist of a basal joint and a chela ; the second appendage consists of seven joints, the remaining four pairs of eight joints ; all these live pairs of appendages are without chelae. The second, third and fourth pairs are similar in structure and bear spines ; the fifth pair are longer than the preceding and without spines ; and the sixth pair are much longer and also larger, with a large quadrate basal ARACHNIDA. EURYPTERIDA 349 joint. The metastoma is oval. The median process of the genital operculum is short in the male, long in the female. Lower Lud- low to Permian. Ex. E. fisckeri, Upper Silurian. Stylonurus. General form similar to Pterygotus. Second, third, and fourth pairs of append- ages with spines ; the two poste- rior pairs very long and slender. Compound eyes near the middle of the prosoma. Tail-spine long, pointed. Body sometimes nearly 5 feet long. Upper Silurian and Old Red Sandstone. Ex. S. pow- riei, same range. Pterygotus (figs. 147, 148). Prosoma rounded in front ; the compound eyes are at the mar- gins. The tail-plate is oval and either bilobed or pointed at its extremity. The pre-oral append- ages are long and chelate ; the second, third, fourth and fifth pairs are similar to each other in size and structure ; the sixth pair long and stout. Metastoma oval. The examples of this genus are often of enormous size, P. anglicus sometimes reaching a length of 6 feet. Lower Ludlow to Old Red Sandstone. Ex. P. anglicus. Old Red Sandstone ; P. bilobus, Upper Silurian. Slimonia (fig. 149). Pro- soma quadrate ; the compound eyes at the anterior angles. Seg- Fig. 149. Slimonia. Restoration of the under surface by M. Laurie, b, metastoma ; c, leaf- like gills seen through the ven- tral plate-like appendages of the mesosoma; g, tail -plate ; I. — VI., appendages of the pro- soma ; VII. — XII., segments of the mesosoma; XIII. — XVIII., segments of the metasoma ; VII. — VIII., genital operculum. Reduced. 350 ARACHNIDA. EURYPTERIDA ments of the mesosoma broader than those of the metasoma. The tail-plate is oval, ending in a pointed process or spine. Metastoma heart-shaped. The pre-oral appendages (chelicerae) are small ; the second pair of appendages are slender, and composed of six joints ; the third, fourth, and fifth pairs have seven joints, and are similar in size and form ; the sixth pair are longer and have a large retort- shaped basal joint. Upper Ludlow and Passage Beds. Ex. S. acuminata, Uppermost Silurian. Distribution of the Eurypterida This Order ranges from the Cambrian to the Permian, but is most abundant in the Upper Silurian and the Old Red Sandstone. The only form known from the Cambrian is Strabops, from Missouri ; from the Ordovician, Echino- gnathus. The chief genera in the Silurian and Old Red Sandstone are Eurypterus, Stylonurus, Pterygotus, Hugh- milleria, and Slimonia; and in the Carboniferous and Permian, Eurypterus. SUB-CLASS II. EU ARACHNIDA The Euarachnids breathe air by means of either pul- monary sacs or tracheae, and the mesosoma is without plate- like appendages. The principal Orders are: — (1) Scor- pionida, (2) Pedipalpi, (3) Araneida, (4) Pseudoscorpionida, (5) Phalangidea, (6) Acarina. ORDER I. SCORPIONIDA The Scorpions (fig. 150) have a long, narrow body, in which three regions are clearly marked. In front, the pfosoma or cephalothorax consists of six fused segments, covered dorsally by a chitinous carapace which bears a pair of simple eyes near its centre, and a group of simple ARACHNIDA. SCORPIONIDA 351 Fig. 150. Ventral view of an Indian Scorpion, Scorpio swammerdami. 1, chelicera ; 2, pedipalp ; 3, 4, 5, 6, walking-legs; 7, genital oper- culum ; 8, pectines ; 9, 10, 11, 12, the four right stigmata leading to the lung-books ; 13, first segment of metasoma ; 14, fourth segment of metasoma ; 15, tail-spine. (From Shipley and MacBride.) x §. 352 ARACHNID A. SCORPIONIDA eyes at each of the two outer front margins. The middle region of the body — the mesosoma or pre-abdomen (7 — 12) — is formed of six free segments, which are short and broad ; the chitinous sheath of each segment consists of a dorsal plate or tergum and a ventral plate or sternum. The posterior portion of the body is the metasoma or post- abdomen (13, 14), and is formed of six segments, each being encased in a complete chitinous cylinder, and all, except the first (13), are narrow ; at the end of the last segment is the tail-spine (15), which bears the poison glands. The anal opening is on the last segment. The prosoma bears six pairs of appendages : — (1) the chelicerce (fig. 150, 1) are small three-jointed limbs with chelae, placed just in front of the mouth ; (2) the pedi- palps (2) are the largest appendages and are at the sides of the mouth; they consist of six joints, ending with chelae, and the basal joints function in mastication; next come four pairs of seven -jointed walking legs (3 — 6) which end in claws, instead of chelae ; the basal joints of the third and fourth pairs assist in mastication. Between the bases of the last two pairs of legs, and immediately in front of the genital operculum, is a small plate, the sternum. On the seventh segment of the body (the first of the mesosoma) there is a small rounded plate — the genital operculum (fig. 150, 7). The eighth segment bears the pectines (s), which are tactile organs and consist of a stem with a row of short processes like the teeth of a comb. On segments nine to twelve, there are, in the adult, no proper appendages ; but a pair of oblique, slit-like open- ings— the stigmata, occur on each of these segments, and lead into pulmonary sacs which contain the lung-books. The metasoma (segments 13 to 18) has no appendages. ARACHNIDA. SCORPIONIDA 353 Although this Order is of great antiquity, it has but few fossil representatives. Palceophonus (fig. 151) occurs in the Silurian rocks of Gothland and Lanarkshire ; Proscorpius in the Silurian of North America. Eoscorpius is found in the Car- boniferous of Scotland, the Mid- lands, and North America. Im- perfect specimens of scorpions have been obtained from the Trias of Warwickshire. One form {Tityus) is known from the Oligocene beds. Eoscorpius does not differ in any important respect from living scorpions, and appears to have been quite as highly or- ganised. Palceophonus (fig. 151), however, is rather more primi- tive in some of its characters ; the walking legs consist of nearly equal-sized joints and seem to be without claws; the basal joints of all these legs could serve to some extent as jaws and in this respect resemble the walking legs of Limulus and still more those of the Eurypterida. Palceophonus, unlike later scorpions, seems to have been aquatic, since it is found associated with marine fossils, and moreover, stigmata appear to have been absent — probably therefore it breathed by means of branchial lamellae instead of lung-books. Fig. 151. Palceophonus cale- donicus from the Upper Silurian of Lesmahago, Lanarkshire. Restoration of ventral surface by R. I. Pocock. x 1£. W. P. 23 354 ARACHNIDA ORDER II. PEDIPALPI The Pedipalpi (' whip-scorpions/ etc.) are represented by Geralinura and Prothelyphonus in the Carboniferous, and by Phrynus in the Tertiary rocks. ORDER III. ARANEIDA Spiders belonging to the genera Protolycosa, Arthroly- cosa, etc., are found in the Coal Measures. In the Oligocene — especially in the amber of Prussia — a large number of forms occur. ORDER IV. PSEUDOSCORPIONIDA (CHERNETIDIA) This Order includes the ' book-scorpions ' (Chelifer) and others. Various forms, belonging to existing genera, occur in the Oligocene amber, e.g. Chelifer, Cherries. ORDER V. PHALANGIDEA (OPILIONINA) Examples of this Order (' harvest-men,' etc.) have been found in the Oligocene amber. The following genera found in the Carboniferous rocks are referred by some writers to the Phalangidea, but are regarded by others as belonging to a distinct Order — the Anthracomarti : — Architarbus, Anthracomartus, Krei- scheria, Eophrynus, Anthracosiro. ORDER VI. ACARINA This Order comprises the mites and ticks. Various forms of mites, belonging chiefly to living genera, occur in the Oligocene amber and other Tertiary deposits. LIST OF PALiEONTOLOGICAL WORKS ABBREVIATIONS A. J. S. American Journal of Science. A. M. N. H. Annals and Magazine of Natural History. G. M. Geological Magazine. Q. J. G. S. Quarterly Journal of the Geological Society. GENERAL Zittel, K. A. von. (1) Handbucli der Palasontologie. 1876-93. (Also in French.) (2) Grundziige der Paheontologie. Ed. 2. 1903. Steinxnann, G. Einfiihrung in die Palaontologie. 1907. Bernard, F. Elements de Paleontologie. 1895. Neumayr, M. Die Stamme des Thierreiches. 1889. McCoy, F. (1) British Palaeozoic Fossils, [pp. 1-184, 1851 ; pp. 185- 406, 1852 ; pp. 407 to end, 1855.] (2) Carboniferous Limestone Fossils of Ireland. 1844. (3) Silurian Fossils of Ireland. 1846. Murchison, R. I. (1) The Silurian System. 1839. (2) Siluria ed. 5. 1872. [For Lower Palaeozoic Fossils.] Phillips, J. Geology of Yorkshire. 1829. [Carboniferous and Mesozoic fossils.] ed. 3 [Part i. Mesozoic]. 1875. Whidborne, G. F. Devonian Fauna of the South of England. 3 vols. 1889-1907. (Palaxmt. Soc.) Rcemer, F. and Freeh, F. Lethaea geognostica. (i) Palaeozoica. 1876- 1902. (ii) Das Mesozoicum. 1903-8. (iii) Das Cainozoicum. 1903-4. Koninck, L. G. de« Faune du Calcaire Carbonifere de Belgique. 6 parts. 1878-87. 23—2 356 PALiEONTOLOGICAL WORKS CATALOGUES OF FOSSILS Bigsby, J. J. (1) Thesaurus Siluricus. 1868. (2) Thesaurus Devonico- Carboniferus. 1878. Bronn, H. G. Index Palaeontologicus. 1S48. Etheridge, It. Fossils of the British Islands. (Palaeozoic.) 1888. Etheridge, B,., jun. Catalogue of Australian Fossils. 1878. Miller, S. A. (1) American Palasozoic Fossils. 1877. (2) North American Geology and Palaeontology. 1889. Morris, J. Catalogue of British Fossils. Second edition. 1854. Sherborn, C. D. Index Animalium. i. 1902. Catalogues of Type Fossils in the following Museums : — Brighton (by E. Crane) ; British Museum (Cephalopoda by G. C. Crick, Blastoidea by F. A. Bather); Bristol (E. Wilson); Cambridge (H. Woods); Manchester (H. Bolton) ; Museum of Practical Geology {H. A. Allen); Norwich (F. Leney) ; York (H. M. Platnauer). FOBAMINIFEBA Brady, H. B. (1) Foraminifera (Challenger Beport). 1884. (2) Car- boniferous and Permian Foraminifera. 1876. (Palajont. Soc.) Btitschli, O. Protozoa, in Bronn's Klassen und Ordn. des Thierreichs. i. 1880-82. Carpenter, W. B. Introduction to the Foraminifera. 1862. Chapman, F. The Foraminifera. 1902. With Bibliography. Jones, T. R., Parker, W. K. and Brady, H. B. Crag Foraminifera. 1866, 1895. (Palaeont. Soc.) Lister, J. J. (1) The Foraminifera (Lankester's Zoology, i. 2). 1903. (2) Dimorphism of Nummulites. Proc. Boy. Soc, 76 B (1905), p. 298. Sherborn, C. D. (1) Bibliography of Foraminifera. 1888. (2) Index to Foraminifera. 1893-6. (Smithsonian Miscell. Coll.) EADIOLABIA Cayeux, L. Organismes dans le Terrain Pre-cambrien. Bull. Soc. geol. France (3), xxn. (1894), p. 197. Also G. M. (1894), p. 419 ; and Banff, Neues Jahrb. fur Min. etc., i. (1896), p. 116. Haeckel, E. (1) Die Badiolarien. 1862. (2) Beport on the Badiolaria (Challenger Beport). 1887. PALiEONTOLOGICAL WORKS 357 Hinde, G. J. (1) Ordovieian Radiolaria. A. M. N. H. (6), vi. (1890), p. 40. (2) Devonian and Carboniferous Radiolaria. Q.J. G.S. xlix. (1893), p. 215; ibid. li. (1895), p. 609; ibid. lv. (1899), pp. 38, 211. Holmes, W. 1YL Chalk Radiolaria. Q. J. G. S. lv. (1899), p. 691. Also ibid. li. (1895), p. 600. G. M. (1895), p. 315. Rust. Radiolarien. Palffiontographica. (Jurassic) xxxi. (1885), p. 269 ; (Chalk) xxxiv. (1888), p. 181 ; (Trias and Palasozoic) xxxviii. (1892), p. 107 ; (Jurassic and Chalk) xlv. (1898), p. 1. PORIFERA Hinde, G. J. (1) Catalogue of Sponges in the Geological Department of the British Museum. 1883. (2) British Fossil Sponges. 1887-93. (Palasont. Soc.) (3) Porosphcera. Journ. R. Micr. Soc. 1901, p. 1. IVIinchin, E. A. Sponges. (Lankester's Zoology, n.) 1900. Polejaeff, N. E. Calcarea (Challenger Report). 1883. Rauff, H. (1) Palaeospongologie. Palaeontographica, xl., 1893-1 ; xli. (1895), p. 223. (2) Receptaculitid®. Abhandl. der math.-phys. Classe d. k. bayer. Akad. xvn. (1892), p. 645. Ridley, S. O. and Dendy, A. Monaxonida (Challenger Report). 1887. Schultze, F. E. Hexactinellida (Challenger Report). 1887. Sollas, W. J. (1) Encyc. Britt. xxn. (1887). (2) Tetractinellida (Challenger Report). 1888. Vosmaer, G. C. J. Porifera, in Bronn's Klassen und Ordn. des Thier- reichs. n. 1887. GRAPTOLITOIDEA Allman, G. J. Morphology and Affinities of Graptolites. A. M. N. H. (4), ix. (1872), p. 361. ' Barrande, J. Graptolites de la Boheme. 1850. Elles, G. L., Wood, E. M. R. and Iiapworth, C. British Graptolites. 1901-08. (Palseont. Soc.) Hall, J. Graptolites of the Quebec group. 1865. Hermann, O. Distribution, Organisation and Economy of Grapto- lithidaB. G. M. (1885), pp. 406, 448. Dichograptidae, ibid. (1886), p. 13. Holm, G. (1) On Didymograptus, Tetragraptus, and Phyllograptus. G. M. (1895), pp. 433, 481. (2) Gotlands Graptoliter. Bih. K. Svenska Yet. Akad. xvi. no. 7 (1890). Hopkinson, J. (1) Morphology of Rhabdophora. A. M. N. H. (5), ix. (1882), p. 51. (2) Reproduction, ibid. (1), vn. (1871), p. 317. 358 PAL.EONTOLOGICAL WORKS Lapworth, C. (1) Distribution of Rhabdophora. A. M. N. H. (5), in. (1879), pp. 245, 449 ; iv. (1879), pp. 333, 423 ; v. (1880), pp. 45, 273, 358 ; vi. (1881), pp. 16, 185. (2) Classification of Rhabdophora. G. M. Vol. x. (1873), pp. 500, 555. Nicholson, H. A. and Marr, J. E. Phylogeny of Graptolites. G. M. (1895), p. 529. Perner, J. Graptolites de la Boheme. Parts i. — in., 1894-99. Ruedemann,R. (1) Development and Mode of Growth of Biployraptus. 14th Ann. Rep. State Geol. New York for 1894 (1895), p. 219. Also A. J. S. ser. 3, xlix. (1895), p. 453. (2) Graptolites of New York, Part I., 1904 ; Part II., 1908. (N. York State Mus. Mem. 7.) Tornquist, S. L. (1) Structure of Diprionidae. Sartryck af Konl. Fysiogr., Handl. Ny Foljd, iv. 1893. (2) Graptolites of Pkyllo- Tetrayraptus Beds. Konl. Fysiogr. Sallsk. Handl. xn. (1901). Walther, J. Die Lebensweise der Graptolithen. Zeitschr. der deutsch. geol. Gesellsch. xlix. (1897), p. 238. Wiman,C. Diplograptidte and Monograptidie. Bull. Geol. Inst. Upsala, i. (1894), pp. 97, 113 ; also Nat. Sci. ix. (1896), pp. 186, 240. STROMATOPOROIDEA Nicholson, H. A. British Stromatoporoidea. 1886-92. (Palreont. Soc.) SCYPHOMEDUS^E Maas, O. Ueber Medusen aus dem Solenhofer Schiefer und der Kreide. Palaeontographica, xlviii. (1902), p. 297. Walcott, C. D. Fossil Medusae. Mon. U. S. Geol. Survey, zxx. 1898. ANTHOZOA (ACTINOZOA) Beecher, C. E. (1) Development of a Palaeozoic Poriferous Coral. Trans. Connecticut Acad., vm. (1893), p. 207. (2) Development of Favositidae, ibid. p. 215. Girty, Amer. Geol. xv. (1895), p. 131. Bernard, H. H/l. Alveopora and the Favositidae. Journ. Linn. Soc. (Zool.) xxvi. (1898), p. 495. Bourne, G. C. (1) The Anthozoa (Lankester's Zoology, Part n.), 1900. (2) Heliopora etc. Phil. Trans. Roy. Soc. clxxxvi. (1895), p. 455. Brook, G. and Bernard, H. 3*1. Catalogue of Madreporarian Corals in the British Museum, i.— iv. 1893-1903. Brown, T. C. Development of Streptelasma. A. J. S. (4), xxm. (1907), p. 277. PAL.EONTOLOGICAL WORKS 359 Carruthers, R. G. (1) Septal Plan of the Rugosa. A. M. N. H. (7), xviii. (1906), p. 356. (2) Revision of Carboniferous Corals. G. M. (1908), pp. 20, 63. Dana, J. D. Zoophytes. (Wilkes Expedition), 1848. Duerden, J. E. (1) Morphology of Madreporaria. Septal Sequence. Biol. Bull., vii. (1904), p. 79 ; ix. (1905), p. 27. (2) Relationships of Rugosa to Zoantheae. A. M. N. H. (7), ix. (1902), p. 381. Duncan, P. M. (1) British Fossil Corals. 1866-72. (Pakeont. Soc.) (2) Revision of the Families and Genera of the Madreporaria. Journ. Linn. Soc. (Zool.) xviii. (1885), pp. 1-204. Dybowski, W. N. Monographic der Zoantharia Rugosa, etc. Arch. fur Naturk. Liv-, Est- und Kurlands. v. 1874. Edwards, H. Milne. (1) Histoire naturelle des Coralliaires. 1857-60. (2) and Haime, J. British Fossil Corals. 1850-54. (Pakeont. Soc.) Freeh, F. (1) Die Korallenfauna der Trias. Palaeontographica, xxxvn. (1890), p. 1. (2) Die Korallenfauna des Oberdevons in Deutschland. Zeitschr. der deutsch. geol. Gesellscb. xxxvn. (1885), pp. 21, 946. Fromentel, E. de. Introduction a l'etude des Polypiers fossiles. 1858-61. Gordon, C. E. Early Stages in Palaeozoic Corals. A. J. S. (4), xxi. (1906), p. 109. Gregory, J. W. Jurassic of Cutch. n. Corals (Palaeont. Indica), 1900. Hickson, S. J. Tubipora. Q. J. Micr. Science, xxm. (1883), p. 556. Hinde, G. J. Arcliceocyatlms, etc. Q. J. G. S. xlv. (1889), p. 125. Kiar, J. (1) Korallenfaunen des norwegischen Silursysterns. Palaeonto- graphica, xlvi. (1899), p. 1. (2) Mittelsilurischen Heliolitiden. Skrift. Videns.-Selsk. i Christiana, i. 10. 1903. Koby, F. (1) Polypiers jurassiques de la Suisse (Mem. Soc. Pal. Suisse). 1881-95. (2) Polypiers cretaces de la Suisse (ibid.). 1896-7. Kunth, A. Foss. Korallen. Zeitsch. d. deutsch. geol. Gesellscb. xxi. (1869), p. 647. Lindstrbm, G. Heliolitidae. Kon. Svensk. Vet. Akad. Handl., xxxn. No. 1 (1899). Gregory, Proc. Roy. Soc, lxvi. (1900), p. 291. Nicholson, H. A. (1) Tabulate Corals of the Palaeozoic Period. 1879. (2) Structure and affinities of Monticullpora and its sub-genera. 1881. (3) Tubipora and Syringopora. Proc. Roy. Soc. Edin., xi. (1880-81), p. 219. (4) and J. Thomson. Study of the chief types of Palaeozoic Corals. A. M. N. H. ser. 4, xvi. (1875), pp. 305, 424 ; xvii. (1876), pp. 60, 123, 290, 451 ; xviii. (1876), p. 68. Ogilvie, M. M. (1) Microscopic and systematic study of Madreporarian Corals. Phil. Trans. Roy. Soc, clxxxvii. (1896), p. 83. Abstract in 'Nature,' lv. (1897), p. 280. (2) Q. J. Micr. Sci., li. (1907), p. 473. (3) Korallen. der Stramberger Schichten. Pakeontographica. Suppl. in. 1897. 360 PAL^ONTOLOGICAL WORKS Ortmann, A. Die Morphologie des Skelettes der Steinkorallen. Zeitschr. fur wiss. Zool., l. (1890), p. 278. Neues Jahrb. fur Min. etc. (1887) ii. p. 185. Quelch, J. J. Eeport on Reef Corals (Challenger Report). 1886. Rominger, C. Fossil Corals. Geol. Surv. Michigan, in. 1876. Sardeson, P. W. Ueber die Beziehungen der fossilen Tabulaten zu den Alcyonarien. Neues Jahrbuch fiir Min. etc. x. (1896), p. 249. Weissermel, Zeitschr. der deutsch. geol. Gesellsch., xlix. (1897), p. 368, and l. (1898), p. 54. Jane?isch, ibid. lv. (1903), p. 486. Schliiter, C. Anthozoen des rheinischen Mittel-Devon. Abhandl. d. preuss. geol. Landes-Anst. vm. 1889. Vaughan, T. W. Eocene and Oligocene Coral Faunas of the United States. Mon. U. S. Geol. Survey, xxxix. 1900. Wentzel, J. Zoantharia Tabulata. Denkschr. d. k. Akad. Wissensch. Math.-nat. CI. Wien, lxii. (1895), p. 479. Wright, E. P. and Studer, T. Alcyonaria (Challenger Report). 1889. ECHINODERMA General Bather, F. A., Gregory, J. W. and Goodrich, E. S. The Echinoderma. (Lankester's Zoology, in.) 1900. Bather, Encyc. Britt. xxvn. 1902. Delage, Y. and Herouard. Zoologie Concrete, in. Echinodermes. 1903. Ludwig, H. and Hamann, O. Echinoderms in Bronn's Klassen und Ordnungen des Thierreichs. n. Edition 2. 1889-1902. Eleutherozoa Agassiz, A. (1) Revision of the Echini. Mem. Mus. Comp. Zool. in. 1872-4. (2) Panamic Deep Sea Echini, ibid. xxxi. 1904. (3) Echinoidea (Challenger Report). 1881. Cotteau, G. and Triger. Echinides de la Sarthe. 1855-69. Desor, E. Synopsis des Echinides fossiles. 1858. Duncan, P. M. (1) Structure of the Ambulacra of fossil Regular Echi- noidea. Q. J. G. S. xli. (1885), p. 419. (2) Revision of the Genera of the Echinoidea. Journ. Linu. Soc. (Zool.), xxin. (1889), p. 1. (3) Palceechinus. A. M. N. H. (6), m. (1889), p. 196. Etheridge, R., jun. (1) Echinothuridae and Perischoechinidae. Q.J. G. S. xxx. (1874), p. 307. (2) Holothuroidea in the Carboniferous. Proc. Roy. Phys. Soc. Edinburgh, vi. (1880-81), p. 183. Forbes, E. (1) Asteriadas in British Strata. (Mem. Geol. Survey. Organic Remains, dec. i.) 1849. (2) Echinodermata of the British Tertiaries. 1852. (Palaeont. Soc.) PALiEONTOLOGICAL WORKS 361 Gregory, J. W. (1) British Cainozoic Echinoidea. Proc. Geol. Assoc, xii. (1891), p. 16. (2) Echinothuridae. Q. J. G. S., liii. (1897), p. 112. (3) Lindstromaster, etc. G. M. (1899), p. 341. (4) Palaeo- zoic Opbiuroidea. Proc. Zool. Soc. (1896), p. 1028. Jackson, R. T. and Jagger, T. A. Melonites. Bull. Geol. Soc. America, vn. (1896), p. 135. Jackson, Palasechinoidea, ibid. p. 171. Lambert, J. Echinides de 1' Infra-Lias et du Lias. Bull. Soc. Sci. de l'Yonne, liii. (1900), p. 3. Loven, S. (1) Echinologica. Bihang Kon. Svensk. Vetenskaps-Akad. Handl. xviii. (4). 1892. (2) Etudes sur les Echinoides. Kon. Svenska Vet. Akad. Handl. xi. No. 7. 1874. Lyman, T. Ophiuroidea (Challenger Report). 1882. Orbigny, A. d\ Paleontologie franyaise. Terr, cret., vi. Echinides irreguliers. 1855-60. Continued by Cotteau. vn. Echinides regu- liers. 1862-7. Terr, jurassiques, ix. Echinides irreguliers. 1867- 74. xi. Echinides reguliers. 1882-89. t Fomel, A. Classification des Echinides. 1883. Howe, A. W. Micraste): Q. J. G. S. lv. (1899), p. 494. Sladen, W. P. (1) Asteroidea (Challenger Report). 1889. (2) and Spencer, W. K. British Fossil Echinoderrnata. n. Cretaceous Asteroidea and Ophiuroidea. 1891-1908. (Palasont. Soc.) Sollas, W. J. Silurian Echinoidea and Ophiuroidea. Q. J. G. S. lv. (1899), p. 692. Stiirtz, B. Beitrage zur Kenntniss palseozoischer Seesterne. Palgeonto- graphica, xxxii. (1886), p. 75; xxxvi. (1890), p. 203. Wright, T. (1) British Oolitic Echinoderrnata. i. Echinoidea (1857- 1878). ii. Asteroidea and Ophiuroidea (1863-1880). (2) British Cretaceous Echinoderrnata. i. Echinoidea. 1864-1882. (Palaaont. Soc.) Pelmatozoa Bather, F. A. (1) British Fossil Crinoids. A. M. N. H. (6), v. (1890), pp. 306, 373, 485; vi. (1890), p. 222; vn. (1891), pp. 35, 389; ix. (1892), pp. 189-202. (2) Terms in Crinoid Morphology, ibid. ix. (1892), p. 51. (3) Crinoidea of Gothland. Part i. K. Vet. Akad. Handl. (Stockholm), xxv. 1893. (4) Vintacrinus. Proc. Zool. Soc. (1895), p. 974. (5) Petalocrinus. Q. J. G. S., liv. (1898), p. 401. (6) Edrioasteroidea. G. M. (1898), p. 543; (1900), p. 193 ; (1908), p. 543. Billings, B. Cystideae of the Lower Silurian Rocks of Canada. (Geol. Survey of Canada : Organic Remains, dec. in.) 1858. Buch, L. von. Ueber Cystideen. Abhandl. d. k. Akad. d. Wiss. zu Berlin (1844), p. 89. 362 PAL^EONTOLOGICAL WOKKS Carpenter, P. H. (1) Crinoidea (Challenger Eeport). 1884-8. (2) Oral and Apical Systems of Echinoderms, Q. J. Micr. Science, xvm. (1878), p. 351; xix. (1879), p. 176. (3) Morphology of Cystidea. Journ. Linn. Soc. (Zool.) xxiv. (1894), p. 1. (4) and Etheridge, It. Catalogue of Blastoidea in the British Museum. 1886. Carpenter, W. B. (1) Antedon. Proc. Boy. Soc, xxiv. (1876), p. 211. (2) Comatula. Phil. Trans., clvi. (1886), p. 671. Forbes, E. Cystidea of the Silurian Bocks of the British Islands. (Mem. Geol. Survey, Vol. n., Part n.) 1848. Jaekel, O. Stammesgeschichte der Pelmatozoen. i. Thecoidea und Cystoidea. 1899. Koninck, L. de and Le Hon, H. Crinoides du Terrain carbonifere de la Belgique. 1854. Waagen, W. and Jahn, J. J. In Barrande's Systeme Silurien du centre de la Boheme. n. 1, Cystidees. 2, Crinoides. 1887-99. Wachsmuth, C. and Springer, F. (1) Revision of the Palasocrinoidea. Proc. Acad. Nat. Sci., Philadelphia, 1879, p. 226; 1881, p. 177; 1885, p. 225 ; 1886, p. 64. (2) Crotalocrinus, ibid. 1888, p. 364. (3) North American Crinoidea Camerata. Mem. Mus. Zool. Harvard, xx., xxi., 1897. (4) Springer, Uintacrinus, ibid. xxv. , 1901. BEACHIOPODA Barrande, J. Systeme Silurien de la Boheme. v. 1879. Beecher, C. E. Development and Classification of Brachiopocla. 'Studies in Evolution' (1901), pp. 229-415. Bittner, A. Brachiopoden der Alpinen Trias. Abhandl. d. kk. geol. Beichsanstalt. xiv., 1890. xvn., 1892. Davidson, T. (1) British Fossil Brachiopoda. 6 vols. 1851-1886. (Palaeont. Soc.) (2) Monograph of Becent Brachiopoda. Trans. Linn. Soc. (Zool.), (2), iv., 1886-88. Deslongchamps, E. Sur le developpement du deltidium. Bull. Soc. geol. de France, (2), xix. (1862), p. 409. Fischer, P. Manuel de Conchyliologie. 1887. [Brachiopods, by CEhlert.] Fischer, P. and CEhlert, D. P. Sur revolution de l'appareil brachial de quelques Brachiopodes. Comptes Bendus, cxv. (1892), p. 749. Friele, H. Development of the Skeleton in Waldheimia. Arch. Math. Nat., ii. (1877), p. 380. Hall, J. and Clarke, J. M. Introduction to the Palaeozoic Brachiopoda. (Geol. Surv. New York, Palaeontology, vin.) i., 1892. n., 1894. King, W. Livgula anatina. A. M. N. H. (4), xn. (1873), p. 1. Schuchert, C. (1) Classification of the Brachiopoda. American Geo- logist, xi. (1893), p. 141; xni. (1894), p. 80. (2) Synopsis of American Fossil Brachiopoda (Bull. U. S. Geol. Surv.). 1897. PAL^EONTOLOGICAL WORKS 363 CILETOPODA Hinde, G. J. Annelid Jaws from the Palaeozoic. Q. J. G. S. , xxxv. (1879), p. 370. Ibid, xxxvi. (1880), p. 368. POLYZOA Busk, G. (1) Polyzoa (Challenger Report). 1884-86. (2) The Crag Polyzoa. 1859. (Palaeont. Soc.) Cumings, E. It. Development of Fenestella. A. J. S. (4), xx. (1905), p. 169. Gregory, J. W. (1) British Palasogene Bryozoa. Trans. Zool. Soc. xiii. (1893), p. 219. (2) Catalogue of Fossil Bryozoa in the British Museum : Jurassic. 1896. (3) Ditto : Cretaceous. 1899. Haime, J. Bryozoaires de la formation jurassique. Mem. Soc. geol. France (2), v. (1854), p. 156. Hincks, T. History of the British Marine Polyzoa. 1880. Orbigny, A. &'. Paleontologie franyaise. Terr. cret. v. 1850-52. Pergens, E. Revision des Bryozoaires du Cretace figures par d'Orbigny. I. Cyclostomata. Ann. Soc. geol. Belg. Mem., Hydr. in. (1889), p. 305. Shrubsole, G. W. (1) Carboniferous Fenestellidaa. Q. J. G. S., xxxv. (1879), p. 275. (2) Silurian Fenestellidae. Ibid, xxxvi. (1880), p. 241. Ulrich, E. O. Lower Silurian Bryozoa of Minnesota. Geol. and Nat. Hist. Surv. Minnesota, in. (1), 1895, p. 96. Vine, G. R. Reports on Fossil Polyzoa. Rep. Brit. Assoc. 1880-92. MOLLUSCA 1. General Adams, H. and A. Genera of Recent Mollusca. 3 vols. 1858. Carpenter, W. Microscopic Structure of Shells. Rep. Brit. Assoc, for 1844 (1845), p. 24; for 1847 (1848), p. 93. Cossmann, M. Catalogue illustre des Coquilles fossiles de l'Eocene des environs de Paris. Vols. i.-v. 1886-92. Fischer, P. Manuel de Conchyliologie. 1887. Morris, J. and Lycett, J. Great Oolite Mollusca. 1850-63. (Palaeont. Soc.) Newton, R. B. List of the Edwards Collection of British Oligocene and Eocene Mollusca in the British Museum. 1891. Pelseneer, P. Mollusca. (Lankester's Zoology, v.) 1907. 364 PAL^ONTOLOGICAL WORKS Sowerby, J. Mineral Conchology of Great Britain. 7 vols. 1812-46. Wood, S. V. Crag Mollusca. 2 vols. 1848, 1850, and supplements. (Palaeont. Soc.) Woodward, S. P. Manual of the Mollusca. Edition 4 by Tate. 1880. 2. Lamellibranchia Amalitzky, W. Ueber die Anthracosien der Perm formation Russlands. Palaeontographica, xxxix. (1892), p. 125. Barrandc, J. Systeme Silurien de la Bobeme. vi. 1882. Bernard, F. (1) Le developpement et la morpbologie de la coquille chez les Lamellibranches. Bull. Soc. geol. de France (3), xxin. (1895), p. 104; xxiv. (1896), pp. 54, 412; xxv. (1897), p. 559. (2) La coquille des Lamellibranches. Ann. Sci. Nat. (Zool.) (8), viii. 1898. Beushausen, L. Die Lamellibranchiaten des rheinischen Devon. Abhandl. d. kk. preuss. geol. Lancles-Anst. xvn. 1895. Cossmann, M. and G. Pissaro. Iconographie des Coquilles de l'Eocene de Paris. I. Pelecypodes. 1904-6. Dall, W. H. (1) The Hinge of Pelecypods. A.J. S. (3), xxxvm. (1889), p. 415. (2) Classification of Pelecypoda. Trans. Wagner Inst. Sci. Philadelphia, in. 1895. Freeh, F. Die devonischen Aviculiden Deutschlands. Abhandl. geol. Specialkarte von Preussen. ix. 1891. Hind, W. (1) Carbonicola, Antlwacoinya, &ndNaiadites. 1894. (2) British Carboniferous Lamellibrauchiata. 1896-1905. (Palaeont. Soc.) Jackson, R. T. Phylogeny of the Pelec.ypoda. The Aviculidse and their allies. Mem. Boston Soc. Nat. Hist. iv. (1890), p. 277. Lycett, J. British Fossil Trigoniae. 1872-79. (PalEeont. Soc.) Neumayr, M. Morpholog. Eintheilung der Bivalven. Denkschr. der k. Akad. der Wissensch. math.-nat. Classe (Wien). lviii. (1891), p. 701. Orbigny, A. d\ Paleontologie francaise. Terr. cret. in. Lamelli- branches. 1843-47. Smith, E. A. Lamellibranchiata (Challenger Report). 1885. Stoliczka, F. Cretaceous Fauna of S. India, in. Pelecypoda (Palaeonto- logia Indica). 1870-71. Wood, S. V. Eocene Bivalves of England. 1861-71. (Palaeont. Soc.) Woods, H. Cretaceous Lamellibranchia of England. 2 vols. 1899- 1908. (Palaeont. Soc.) Vest, W. Ueber die Bildung und Entwicklung des Bivalven-Schlosses. Verhandl. u. Mittheil. siebenbiirg. Vereins. xlviii. (1898), p. 25. Zittel, K. A. Die Bivalven der Gosaugebilde. Denkscbr. d. k. Akad. d. Wissensch. xxiv. (2) (1865), p. 105; xxv. (2) (1866), p. 77. PAL^ONTOLOGICAL WORKS 365 3. Gasteropoda Cossmann, M. Essais cle Paleoconchologie conxparee. 8 parts. 1895- 1909. Donald, J. Murchisonia, etc. Q. J. G. S. li. (1895), p. 210; xliii. (1887), p. 617 ; liv. (1898), p. 45 ; lv. (1899), p. 251 ; iaiii. (1902), p. 313 ; lxi. (1905), pp. 561, 567; lxii. (1906), p. 552. Hudleston, W. H. (1) British Inferior Oolite Gasteropoda. 1887-96. (Palseont. Soc.) (2) and Wilson, E. Catalogue of British Jurassic Gasteropoda. 1892. Koken, E. Ueher die Entwickelung der Gastropoden vom Carnbrium bis zur Trias. Neues Jahrb. fiir Min. etc. vi. (1889), p. 305. Iiindstrom, G. Silurian Gasteropoda and Pteropoda of Gotland. 1884. Felseneer, P. Pteropoda (Challenger Report). 1888. Perner, J. Systeme Silurien de la Boheme. iv. Gasteropodes. 1903. Rochebrune, A. T. de. Monog. des especes foss. des. Polyplaxiphores. Ann. Sci. Geol. xiv. (1883), p. 1. Watson, R. B. Scaphopoda and Gasteropoda (Challenger Report). 1886. Wilson, E. British Liassic Gasteropoda. G. M. (1887), pp. 193, 258. Zittel, K. A. Die Gastropoden der Stramberger Schichten. (Palasont. Mittheil.) 1873. 4. Conularia, Hyolithes, etc. Holm, G. Sveriges Kambrisk-Siluriska Hyolithidffi och Conularides. Sveriges Geol. Undersok. Ser. C. No. 112. Stockholm, 1893. Novak, O. Revision der palaozoischen Hyolithiden Bbhmens. Abhandl. der bohm. Gesellschaft der Wissensch. iv. 1891. Ruedemann, R. A sessile Conularia. Amer. Geol. xvn. (1896), p. 158 ; xviii. (1896), p. 65. Slater, I. L. British Conularise. 1907. (Palsont. Soc. ) Zelizko, J. V. Hyolithes. Centralbl. fiir Min. etc. (1908), p. 362. 5. Scaphopoda Gardner, J. S. Cretaceous Dentaliidre. Q. J. G. S. xxxiv. (1878), p. 56. Newton, R. B. and Harris, G. F. British Eocene Scaphopoda. Proc. Malacol. Soc. i. (1894), p. 63. Richardson, L. Liassic Dentaliidae. Q. J. G. S. lxii. (1906), p. 573. 366 PAL.EONTOLOGICAL WORKS 6. Cephalopoda Appellor, A. Die Schalen von Sepia, Spirula und Nautilus. Kon. Sven. Vetenskaps-Akad. Handl. xxv. 7 (1893). Barrande, J. Systeme Silurien du centre de la Boheine. n. (in 6 parts). Cephalopodes. 1867-70. Blake, J. F. British Fossil Cephalopoda. Part i. Silurian. 1882. Branco, W. Entwickelungsgeschichte der fossilen Cephalopoden. Palffiontographica. xxvi. (1879), p. 19 ; xxvu. (1880), p. 17. Buctman, S. S. Inferior Oolite Ammonites. 1887-1907. (Palaeont. Soc.) Crick, G. C. (1) Muscular Attachment in Ammonoidea. Trans. Linn. Soc. (Zool.), ser. 2, vn. (1898), p. 71. (2) Belemnites. Proc. Malacol. Soc. n. (1896), p. 117 ; vn. (1907), p. 269. Foord, A. H. (1) Carboniferous Cephalopoda of Ireland. 1897-1903. (Palaeont. Soc.) (2) and Crick. Catalogue of the Fossil Cephalo- poda in the British Museum. Parts i.-iii. 1888-97. Freeh, F. Ueber devonische Ammoneen. Beitr. z. Geol. Osterr.-Ung. u. d. Orients, xiv. 1902. Grossouvre, A. de. Les Ammonites de la Craie sujDerieure. (Mem. explicat. Carte geol. de la France.) 1893. Holm, G. Organisation einiger silurischer Cephalopoden. Palaeont. Abhandl. in. 1885. Huxley, T. H. Structure of Beleronitidae. (Mem. Geol. Survey.) 1861. Hyatt, A. (1) Fossil Cephalopods. Bull. Mus. Comp. Zool. Harvard. in. no. 5. 1872. (2) Genesis of Arietidae. Smithsonian Contrib. xxvi. 1889. (3) Phylogeny (chiefly Nautiloidea). Proc. Amer. Phil. Soc. xxxn. (1891), p. 349. Konen, A. v. Ammonitiden d. norddeutsch. Neocom. Abhandl. d. preuss. geol. Landesanst. xxiv. 1902. affojsisovics von SHojsvar, E. (1) Die Cephalopoden der mediterranen Triasprovinz. Abhandl. d. kk. geol. Beichsanst. x. 1882. (2) Die Cephalopoden der Hallstiitter Kalk. Ibid, vi., i. 1873 ; ii. 1893. Neumayr, M. I. Jura Studien. Ueber Phylloceraten. Jahrb. d. kk. geol. Reichsanstalt. xxi. (1871), p. 297. Neumayr, M. and Uhlig, V. Ueber Ammonitiden aus den Hilsbiklungen Norddeutschlands. Palaeontographica, xxvn. (1881), p. 135. Newton, R. B. and Harris, G. F. British Eocene Cephalopoda. Proc. Malacol. Soc. i. (1891), p. 119. Orbigny, A. d'. Paleontologie francaise. Terr. cret. i. 1840-41. Terr, jurassiques, i. 1842-49. Phillips, J. British Beleinniticlae. 1865. (Palaeont. Soc.) Pompeckj, J. F. Revision d. Ammoniten d. schwabischen Jura. 1893, 1896. PAL^ONTOLOGICAL WORKS 367 Quenstedt, F. von. Die Arninoniten des schwabischen Jura. 1883-89. Schliiter, C. Cephalopoden der oberen deutschen Kreide. Palaeonto- graphica, xxi., xxiv. , 1871-76. Sharpe, D. Mollusca in the Chalk of England. Cephalopoda. 1853-4. (Palffiont. Soc.) Smith, J. P. Carbonif. Ammonoids. U. S. Geol. Surv. Mon. 42. 1903. "Wright, T. Lias Ammonites. 1878-86. (Palaeont. Soc.) Wiirtenberger, L. Uber die Stammesgeschichte der Ammoniten. 1880. Zittel, K. A. Die Cephalopoden der Stramberger Schichten. 1868. ARTHROPODA 1. Crustacea Amnion, L. von. Beitrag zur Kenntniss der fossilen Asseln. Sitz. d. kk. Akad. d. Wissensch. math.-phys. Classe. iv. (1882), p. 507. Barrande, J. Systeme Silurien de la Boheme. Trilobites. 1852. Supplement 1872. Bate, C. S. Crustacea Macroura (Challenger Report). 1888. Beddard, F. E. Isopoda (Challenger Report). 1884, 1886. Beecher, C. E. Structure and Development of Trilobites. ' Studies in Evolution ' (1901), pp. 109-225. G. M. (1902), p. 152. Bell, T. Fossil Malacostraca. 1857-62. (Palaeont. Soc.) Bernard, H. M. Systematic Position of the Trilobites. Q. J. G. S. l. (1894), p. 411 ; li. (1895), p. 352. Caiman, W. T. Crustacea (Lankester's Zoology, vn. 3). 1909. Darwin, C. (1) Fossil Lepadidae. 1851. (2) Fossil Balanidae. 1854. (Palaeont. Soc.) Edwards, H. Milne. Histoire naturelle des Crustacees, 1834-40. Fritsch, A. See under Arachnida. Hall, J. and Clarke, J. M. Trilobites and other Crustacea, Lower Palaeozoic. (Geol. Survey of New York. Palaeont. vn.) 1888. Huxley, T. H. Pijgocephalus from Coal. Q. J. G. S. xm. (1857), p. 363. Jones, T. R. (1) Fossil Estheriae. 1862. (2) Tertiary Entomostraca. 1856, 1889. (3) Cretaceous Entomostraca. 1849, 1890. (Palaeont. Soc.) (4) and Woodward, H. British Palaeozoic Phyllocarida. 1888-92. (Palaeont. Soc.) Jones, T. R., Kirkby, J. W. and Brady, G. S. British Entomostraca from the Carboniferous. 1874-84. (Palaeont. Soc.) Lake, P. British Cambrian Trilobites. 1906- . (Palaeont. Soc.) Lapworth, C. Olenellus callavei. G. M. (1891), p. 529. Iiindstrom, G. Visual Organs of Trilobites. Kon. Svenska Vet. Akad. Handl. xxxiv. 1901. 368 PAL^ONTOLOGICAL WORKS Miers, E. J. Brachyura (Challenger Report). 1886. Oppel, A. Ueber jurassische Crustaceen. (Palseont. Mittheil.) 1862. Packard, A. S. N. American Phyllopod Crustacea. (Geol. Survey of the Territories 12th Ann. Rep.) 1883. Peach, B. N. (1) Olenellus in N. W. Highlands. Q. J. G. S. xlviii. (1892), p. 227; l. (1894), p. 661. (2) Higher Crustacea of the Carboniferous of Scotland. Mem. Geol. Surv. 1908. Salter, J. W. British Trilobites. 1861-1883. (Paheont. Soc.) Sars, G. O. Report on Phyllocarida (Challenger Report). 1887. Smith, G. Anaspidacea. Q. J. Micr. Sci. liii. (1909), p. 489. Stebbing, T. R. R. Amphipoda (Challenger Report). 1888. Vogdes, A. Bibliography of Palaeozoic Crustacea. Ed. 2, 1893. Walcott, C. D. (1) Fauna of the Lower Cambrian or Olenellus zone. (Ann. Rep. U. S. Geol. Survey.) 1890. (2) The Trilobite : New and Old Evidence. (Bull. Mus. Comp. Zool., vm.) 1881. Woodward, H. (1) Catalogue of British Fossil Crustacea. 1877. (2) British Carboniferous Trilobites. 1883-4. (Paheont. Soc.) (3) Pygocephalus. G. M. (1907), p. 400. (4) Prceanaspides. G. M. (1908), p. 385. (5) and Salter. Chart of Fossil Crustacea. 1865. 2. Myriapoda Peach, B. N. Myriapods from the Old Red Sandstone of Forfarshire. Proc. Roy. Phys. Soc. Edin. vn. (1882), p. 77 ; xiv. (1899), p. 113. Scudder, S. H. (1) Archipolypoda, a type of Carboniferous Myriapods. Mem. Boston Soc. Nat. Hist. in. (1882), p. 143. (2) Two new types of Carboniferous Myriapods, ibid. in. (1884), p. 285. "Woodward, H. Carboniferous Myriapods. G. M. (1887), p. 1. 3. Insecta Brodie, P. B. Insects in the Secondary rocks of England. 1845. Brongniart, C. L'histoire des Insectes des Temps Primaires. Bull. Soc. Industr. Min. St Etienne. Ser. 3, vn. 1893. Handlirsch, A. (1) Die fossilen Insekten und die Phylogenie der rezenten Formen. 1906. (2) Revision of American Palaeozoic Insects. Proc. U. S. Nat. Mus. xxix. (1906), p. 661. Scudder, S. H. (1) Index to the Fossil Insects, including Myriapods and Arachnids. Bull. U. S. Geol. Survey, 1891. (2) Bibliography of Fossil Insects, ibid. 1890. (3) Palasodictyoptera. Mem. Boston Soc. Nat. Hist. in. (1885), p. 319. (4) Fossil Insects of North America. 1890. PAL^EONTOLOGICAL WORKS 3G9 4. Arachnida Fritsch, A. (1) Fauna derGaskokle, etc. iv. 1901. (2) Palasozoische Araclmiden. 1904. Holm, G. Eurypterus. Mem. Acad. Iniper. Sci. St. Petersbourg (8), vin. 1898. Huxley, T. H. and Salter, J. W. Pterygotus. (Mem. Geol. Survey, Organic Eemains.) 1859. Laurie, Bd. Eurypterida. Trans. Roy. Soc. Edinburgh, xxxvu. (1892), p. 151, (1893), p. 509 ; xxxix. (1899), p. 575. Peach, B. N. Scorpions from the Carboniferous of Scotland and the English Borders. Trans. Roy. Soc. Edin. xxx. (1881), p. 397, (1882), p. 511. Focock, It. I. Silurian Scorpion. Q. J. Micr. Sci. xliv. (1901), p. 291. Schmidt, F. Die Crustaceenfauna der Eurypterusschichten von Rootzi- kiill. Mem. Acad, imper. St Petersb. (7), xxxi. (1883), p. 28. Woodward, H. (1) The Xiphosura. Q. J. G. S. xxm. (1867), p. 28 ; xxviii. (1872), p. 46. (2) The Merostomata. 1866-78. (Palteont. Soc.) w. p. 24 INDEX Names of genera are printed in italics Abactinal, 108 Aboral, 108 Abyssal zone, 185, 253 Acalephas, 73 Acanthin, 29 Acanthopores, 192 Acanthoceras, 278 Acanthotelson, 323 Acanthoteuthis, 287 Acanthothyris, 182 Acarina, 354 Acaste, 307 Acephala, 200 Acervularia, 88 Acetabulum (Echinoidea), 122 Acidaspis, 309 Acorn shells, 316 Acrosalenia, 127 Actceon, 249 Actinal surface, 108 Actinaria, 77 Actinocamax, 284 Actinoceras, 264 Actinocrinus, 141 Actinometra, 145 Actinopteria, 214 Actinostroma, 71 Actinozoa, 71-104 Ad-ambulacral plates, 108 Adductor impressions, 202 Adductor muscles, 165, 166, 200, 313, 319 JF,ger, 329 JEglina, 307 JEgoceras, 275 JEquipecten, 215 Agelacrinus, 157 Aglaophenia, 55 Aglaspis, 343 (footnote) Agnostus, 303 Alar fossula, 78, 85 Alar septum, 84 Alaria, 244 Alcyonaria, 93-98, 103 Alcyonium, 94, 103 Alectryonia, 217 Allorisma, 230 Alveolaria, 195 Alveolina, 22 Alveolites, 99 Alveopora, 98, 99 Amaltheus, 276 Amber, 5, 333-337, 354 Amberleya, 240 Ambony cliia, 230 Ambulacral area, 118-120, 124, 156 „ groove, 108, 112, 157 ,, ossicle, 108, 113 plate, 118-120, 140 ,, surface, 108 Ambulacrum = ambulacral area Ammonites, 272 (footnote) Ammonoidea, 266, 285 Amnigenia, 230 Amoeba, 15 Amphidromus, 255 Amphipoda, 326 Amphipora, 73 Amphistegina, 24 Amphiura, 115 Amphoracrinus, 142 Amplexus, 91 Ampulla, 110 24—2 372 INDEX Ampyx, 303 Amusium, 215 Andbacia, 104 Anal inter-radial, 139 ,, siphon, 200 Ananchytes, 131 Anarcestes, 271 Anaspides, 323 Ancilla, 247 Ancillaria, 247 Ancyloceras, 279 Angelina, 305 Angle of divergence, 58 Anisopleura, 238 Annelida, 158 Annulus, 261 Anodonta, 218 Anomia, 215 Anomura, 328 Antedon, 145, 146 Antenna, 290, 298, 312, 314, 316, 318, 320, 328, 332, 333 Anterior canal, 235 Anthozoa, 74-104 Anthracodesmus, 333 Anthracomarti, 354 Anthracomartus, 354 Anthracomya, 218 Anthracosiro, 354 Anthracosia, 218 Anthrapalcemon, 325 Anti-ambulacral, 108 Antipatharia, 77 Ants, 337 Apex (Gasteropoda), 233 Aphidae, 336 Apical disc, 116 Apiocrinus, 144 Aporosa, 86, 92 Aporrhais, 244 Aptera, 334 Aptychopsis, 322 Aptychus, 268 Apus, 302, 312, 313 Apygia, 170 Arachnida, 337 Aragonite, 3-5, 76, 207 Araneida, 354 Area, 211 Arcestes, 273 Archceocidaris, 125 Archceoniscus, 325 Archanodon, 230 Archianellida, 158 Archidesmus, 333 Archimedes, 195 Architarbus , 354 Arctica, see Gyprina Area, 163, 205 Arenaceous Forarninifera, 17, 22, 26 Areola, 122 Arethusina, 311 Argonauta, 280, 284 Arietites, 275 Aristocystis, 147 Aristotle's lantern, 124 Arms (Asteroidea), 107 ,, (Brachiopoda), 161, 166 ,, (Cephalopoda), 257, 279, 281, 283, 284 „ (Crinoidea), 136, 139 ,, (Ophiuroidea), 112 Artemis, 224 ArtJirolycosa, 354 Arthropleura, 325 Arthropoda, 288 Arthropomata, 170 Arthrostraca = Amphipoda + Iso- poda, 325 Articulata, 162, 173-184 Asaphellus, 306 Asaphus, 306 Ascoceras, 264 Asiphonida, 210 Aspidocaris, 323 Aspidoceras, 287 Aspidosoma, 112 Aspidura, 115 Astarte, 219 Asteractinella, 36, 44, 48 Aster obi astus, 155 Asteroidea, 107-112 Asthenosoma, 121 Astrceospongia, 36, 44, 47 Astroccenia, 104 Astropecten, 112 Astrorhizse, 71 Astylospongia, 42, 47 Atelostomata, 129 Athyris, 180 Atractilites, 284 Atractites, 287 Atremata, 171 INDEX 373 A try pa, ISO Aturia, 265 Aucella, 214 Aulacoceras, 284 Aulacothyris, 183 Aurelia, 73 Auricles (Echiuoidea), 124 Auriform gasteropods, 237 Autozooids, 96 Auxiliary lobes, 267 Avellana, 249 Avicula, 213 Avicularia, 190, 194 Aviculopecten, 216 Axial caual, 35 „ furrow, 293 Axillare, 139 Axincea, 211 Axis (Trilobita), 297 Bactrites, 269, 287 Baculites, 273 Bairdia, 315 Bakevellia, 231 Bala mis, 316, 317 Barbados Earth, 30 Barnacles, 316 Barroisia, 46 Basal budding, 81 ,, epitbeca, 81 ,, plates, 139, 149 Basipodite, 290 Bees, 337 ' Beetles, 336 Belemnitella, 284 Belemnites, 281 Belemnoteuthis, 284 Belinurus, 342 Bellerophon, 239 Beloptera, 287 Belosepia, 283, 286 Berenicea, 192 Beyrichia, 314 Bigeminal, 120 Bilateral symmetry, 75, 86, 124, 129, 196, 231, 237, 256, 289 Bilobites, 177 Biloculina, 22 Biplication, 168 Biramous appendages, 290, 318, 323, 327 Biserial crinoids, 139 Biserial graptolites, 58 Bivalved carapace, 312, 313, 319 shells, 160, 197 Blastoidea, 149-155 Blastoidocrinus, 155 Blastostyle, 53 Blattidas, 335 Blue coral, 96 Body-cavity, 105, 160, 197 Body-chamber, 261 Book-scorpions, 354 Boring lamellibranchs, 10, 209 Boss, 122 Bothriocidaris, 121, 133 Botryocrinus, 142 Bougainvillea, 53 Bourguetia, 254 Bourgueticrinus, 144 Brachial plates, 139 ,, skeleton, 166, 167 Brachiole, 146, 148, 153 Brachiopoda, 160-187 Bracliylepas, 317 Brachymetopus, 311 Brachyura, 330 Branchiae, 110, 123, 199, 289 Branchial siphon, 200 Branchiopoda, 312 Branchipus, 302 Brittle-stars, 112 Bronteus, 307 Bryograptus, 68 Bryozoa, 188-195 Buccal plate, 113 Buccinopsis, 255 Baccinum, 245 Budding (corals), 80 Bulla, 249 Bunodes, 342 Butterflies, 335 Byssal sinus, 209 Byssus, 199, 209 Caddis-flies, 335 Cadomella, 187 Calamary, 279 Calamophyllia, 104 Calcarea, 45, 47 Calcarina, 24 Calceocrinus, 145 Calceola, 91 Calcispongise, 45 374 INDEX Calcite, 3-5, 45, 106, 168, 207 Calicular budding, 81 Calliderma, 111 Gallista, 224 Callograptus, 55 Callus, 235 Calymene, 305 Calyptoblastea, 53, 56, 63 Galyptraa, 242 Calyx (Mastoids), 149 ,, (corals), 77 ,, (crinoids), 136 ,, (cystideans), 146 ,, (edrioasteroids), 156 Camarophoria, 178 Camerospongia, 49 Camarotccchia, 182 Camp anularia, 53 Camptonectes, 215 Caninia, 91 Gapulus, 242 Garabocrinus, 154 Carapace, 290, 312, 313, 337, 340, 343, 350 Carbonicola, 218 Carbonisation, 6, 56 Cardiaster, 131 Cardinal fossula, 78, 85 ,, process, 166 ,, septum, 83 teeth, 204 Card i nia, 218 Cardioceras, 211 Cardiola, 228 Cardiomorpha, 228 Cardita, 220 Cardium, 223 Carina, 316 Caryocaris, 322 Cassianella, 231 C 'atopy gus, 130 Caudal fork, 312, 320 Cell, 15 Cellepora, 194 Centipedes, 332 Central capsule, 28 ,, disc, 58 Cephalic shield, 293 Cephalites, 49 Cephalopoda, 257-287 Cephalothoracic shield, 318, 323, 325-327 Cephalothorax. 290, 337, 339, 343, 350 Ceratiocaris, 321 Ceratites, 272 Ceratosa, 40 Ceriopora, 195 Gerithium, 243 Ceromya, 227 Cervical suture, 328 Chcetetes, 101 Chffitopoda, 158 Chama, 221 Cliasmops, 307 Cheeks (Trilobita), 293 Cheilostomata, 193 Cheirurus, 308 Chehe, 328, 346 Chelicera, 337, 340, 352 Ghelifer, 354 Chernes, 354 Chernetidia, 354 Chert, 30 . Chilaria, 340, 346 Chilopoda, 332 Chirodota, 135 Chitin, 3, 5, 17, 52, 56, 169, 289, 338, 343, 350 Chiton, 237, 238 Chlamys, 215 Chonetes, 175 Ghrysodomus, 246 Cidaris, 126 Cilia, 16 Cirri, 137 Cirripedia, 316 Cirrus, 240 Cladiscites, 287 Cladocera, 312 Cladochonus, 80 Cladopliyllia, 104 Class, 13 Classification, 13 Clathrodictyon, 73 Clavella, 246 CUmacograptus, 69 Glisiophyllum, 89 Clistenterata, 170 Clonograptus, 67 Clymenia, 270 Clypeus, 130 Cockroaches, 335 Codaster, 154 INDEX 375 Ccelentera, 50-104 Coelenteron, 50, 51, 74 Coelom, 105 Ccelonautilux, 265 Caloptychium, 36 Ccenenchyma, 81, 82, 96 Ccenograptus, 68 Coenosarc, 51, 56, 57, 81, 82 Coenothyris, 183 Culeolus, 256 Coleoptera, 336 Colloid silica, 34, 35 Colhjrites, 130 Columella (Corals), 78 ,, (Gasteropoda), 234 Columnal, 137 Common canal, 56, 58 Communication-plates, 191 Compound sponge, 34 Concentric operculum, 236 Gonchidium, 178 Conical gasteropods, 236 Conjugate pores, 120 Gonocardium, 214 Conocephalltes, 304 Conoceras, 286 Conocoryphe, 304 Conorbis, 255 Conotheca, 283 Gonularia, 255, 256 Conulus, 129 Gonus, 248 Convergence, 14 Convolute gasteropods, 237 Copepoda, 291 Coralline zone, 253 Corallite, 77 Corallium, 94, 103 Corallum, 77 Corals, 74-104 Corbicula, 220 Corbula, 225 Corona, 116, 118, 121 Corticata, 15 Corynella, 45 Cosmoceras, 278 Cost®, 79 Cottaldia, 133 Counter fossula, 78, 85 ,, septum, 83 Covering-plates, 139, 146 Coxopodite, 290, 299 Crabs, 327, 330 Crangopsis, 325 Crania, 173 Crassatella, 220 Crassatellites, 220 Craticularia, 39 Crayfish, 327 Crenulate tubercles, 122 Cribrilina, 194 Crickets, 335 Crinoidea, 136-146 Crioceras, 279 Crisina, 195 Cristellaria, 23 Crotalocrinus, 142 Crustacea, 289 Cryptostomata, 193 Ctenodonta, 211 Ctenophora, 50 Ctenostomata, 191 Cucullcea, 211 Cumacea, 318 Cupressocrinus, 145 Cuttle-bone, 280 Cuttle-fish, 257, 279 Cyathaxonia, 90 Cyathocrinus, 142 Cyathocystis, 157 Cyathophi/lluni, 88 Cybele, 309 Cyclolites, 104 Cyclolobus, 287 Cyclonema, 254 Gyclophyllum, 90 Cyclosphceroma, 325 Cyclostomata, 191 Cylindrical gasteropods, 236 Cymaclymenia, 271 Cyphosoma, 128 Cyprcea, 245 Cypridea, 315 Cypridina, 315 Gyprina, 219 Cypris, 315 Gyrena, 220 Ctyrtfa, 180 Cyrtoceras, 265 Cyrtoclymenia, 271 Cyrtodonta, 230 Cyrtograptus, 69 Cystidea, 146-149 Cystiphyllum, 91 376 INDEX Cy there, 315 Cytherea, 224 Dactylioceras, 276 Dactylopores, 70 Dactylozooid, 53, 71 Dalmanella, 177 Dalmanites, 307 Daphnia, 312 Decapoda (Cephalopoda), 281 ,, (Crustacea), 327 Deiphon, 308 Delthyrium, 161 Deltidium, 164 Deltoid plates, 151 Demi-plates, 119 Demospongiae, 40-44 Dendrocrinus, 145 Dendrograptus, 55 Dendroid corals, 81 „ graptolites, 55 Dendrophyllia, 80, 104 Dental plates, 162 Dentalina, 17 Dentalium, 257 Dermal branchiae, 110 ,, layer (sponges), 31 Desmas, 42 Desmoceras, 287 Desmodont, 204, 226, 230 Development of graptolites, 61 ,, of corals, 79, 83 ,, of brachial skeleton, 167 ,, of ammonoids, 270 ,, of trilobites, 300 Dextral gasteropods, 233 Diademopsis, 133 Diastopora, 195 Dibranchia, 279 Dibunophyllum, 90 Dicellograptus, 68 Die eras, 221 Dichograptus, 67 Dicranograptus, 68 Dicroloma, 244 Dictyograptus, 55 Dictyonema, 55 Diet yophy ton, 39 Dictyothyris, 183 Dicyclic crinoids, 139, 142 Didymograptus, 67 Dielasma, 183 Dimorphism, 19 Dimorphograptus , 69 Dimyaria, 200, 202, 209 Diplograptus, 68 Diplopoda, 332 Diplopodia, 128 Diprionidian = biserial, 58 Diptera, 336 Disc (Asteroidea), 107 ,, (Ophiuroidea), 112, 113 Discina, 172 Discinisca, 172 Discinocaris, 322 Discites, 265 Discitoceras, 265 Discoidal gasteropods, 236 Discoidea, 129 DiscomedussB, 73 Dissepiments, 79, 80, 82 Distal end, 57 Dithyrocaris, 322 Divaricator muscles, 165, 166 Dorsal cup, 137 surface, 108, 201 Dory derma, 43 Dosinia, 224 Douvilleiceras, 287 Dragon-flies, 335 Dreissensia, 231 Dromia, 330 Dysodont, 203, 211, 229, 230 Ears (Lamellibranchs), 205 Earwigs, 335 Ecardines, 170 Echinobrissus, 130 Echinocaris, 323 Echinoconus, 129 Echinocorys, 131 Echinocrinus, 125 Echinocyamus, 135 Echinocystis, 133 Echinoderma, 105-157 Echinognathus, 350 Echinoidea, 115-135 Echinosphara, 148 Echinothuria, 121 Echinus, 128 Ectocyst, 189 Ectoderm, 50, 70, 115 Ectoprocta, 191 INDEX 377 Edmondia, 228 Edrioaster, 156, 157 Edrioasteroidea, 156 Eleutherozoa, 107-135 Ellipsocephalus, 311 Elongate gasteropods, 236 Emarginula, 239 Eiicrinurus, 308 Encrinus, 143 Endoceras, 286 Endoderm, 50 Endopodite, 290, 299, 300 Endothyra, 23, 27 Enoploclytia, 330 Entalophora, 192 Entomis, 314 Entomostraca, 291 Entoprocta, 191 Eophrynus, 354 Eoscorpius, 353 Eospharoma, 326 Ephemeridae, 335 Epiaster, 123 Epistoma, 346 Epitheca, 77 Equus, 13 Erodona, 231 Eryma, 330 .En/on, 329 Eryonidse, 331 Escutcheon, 202, 205 Estheria, 312 Euarachnida, 350 Eucalyptocrinus, 141 Eucladia, 115 Eucorystes, 331 Eudesia, 183 Euomphalus, 240 Euphoberia, 333 Euproops, 342 Eurycare, 305 Eurypterida, 343 Eurypterus, 348 Euthyneura, 233, 248 Evolution, 11-13 Excurrent canals, 33 Exhalent canals, 33 Exogyra, 217 Exopodite, 290, 299, 300 Exsert septa, 78 Eye-line, 295 Eyes (Eurypterida), 343 Eyes (Lamellibranchs), 201 ,, (Scorpions), 351 ,, (Trilobites), 295 ,, (Xiphosura), 340 Fabularia, 22 Facetted pleurae, 297 Facial suture, 294 Family, 13 False columella, 79 Fascicularia, 192 Fasciole, 123 Favosites, 99 Feather-stars, 136 Fenestella, 193 Fission, 51, 80, 81 Fissurella, 239 Fissuridia, 239 Fixed brachial, 140 ,, cheek, 294 ,, lamellibranchs, 209 Flabellum, 92 Flagellata, 15 Flagellum, 16, 32 Fleas, 336 Flesh-spicules, 35, 38, 41, 42 Flies, 336 Flint, 7 Floscelle, 124 Food-groove, 136, 140, 146, 152 Foot (Cephalopoda), 258 ,, (Gasteropoda), 232 ,, (Lamellibranchia), 197 ,, (Mollusca), 197 ,, (Scaphopoda), 256 Footprints, 8 Foramen, 164 Foraminifera, 16-28 Forriculidas, 335 Fossilisation, 2-8 Fossula, 78, 85 Free cheek, 294 Freshwater lamellibrauchs, 230 Fulcrum, 297 Fulgoridae, 336 Funnel, 257, 280 Fur caster, 115 Fusiform gasteropods, 236 Fusulina, 24, 27 Fusus, 246 Galerites, 129 24—5 378 INDEX Galeropygus, 133 Gammarus, 326 Gampsonyx, 323 Gaping (Lamellibranchs), 208 Gari, 225 Gasteropoda, 231-255 Gastral cavity, 31 ,, layer, 31 Gastrioceras, 272 Gastropores, 70 Gastrozooid, 53, 70 Genal angle, 294 ,, spine, 294 Genital operculum, 340, 347, 352 ,, plates, 117 Genus, 13 Geocoma, 115 Geodites, 36, 42, 47 Geoteuthis, 286 Geralinura, 354 Gervillia, 213 Gills, 123, 199, 232, 237, 259, 289, 325, 326, 327, 328, 337, 341, 347 Gissocrinus, 145 Glabella, 293 Gladius, 280 Glauconite, 7, 37 Globigerina, 24, 26 Globular gasteropods, 237 Glycimeris, 211 Glyphea, 329 Glyphioceras, 271 Glyptarca, 230 Glyptocrinus, 145 Glyptoscorpius, 347 Glyptosphcsra, 146 Gnathobase, 299 Gnathostomata, 129 Gnats, 336 Gomphoceras, 264 Gonangiurn, 52, 61 Goniatites, 271 (footnote) Gonioclymenia, 271 Goniomya, 227 Goniophyllum, 92 Goniopora, 93 Gonocyst, 192 Gonoecium, 192 Gonophore, 51 Gonotheca, 50, 52 Gorgonia, 94, 103 Grammysia, 228 Granatocrinus, 155 Grantia, 33, 36 Granules, 121, 122 Graphularia, 103 Graptolites, 56-70 Graptolitoidea, 56-70 Gresslya, 227 Griffithides, 310 Gryllidas, 335 Gryphcea, 217 Gryphochiton, 238 Guard of Belemnites, 281 Guettardia, 49 Gymnoblastea, 52 Gymnolgema, 191 Gymnomyxa, 15, 16 Gypidula, 178 Haematite, 8 Halichondria, 36 Hallirhoa, 44 Halobia, 231 Halysites, 101 Hamites, 274 Haploceras, 287 Haplocrinus, 145 Haplocecia, 195 Harpes, 303 Harpoceras, 276 Harvest-men, 354 Head-shield, 293 Heliolites, 99 Heliopora, 96, 97, 100, 103 Heliosphcera, 28 iM.r? 250 Helminthochitoii, 238 Hemiaspis, 342 Hemiaster, 132 Hemicidaris, 127 Hemipedina, 127 Hemiptera, 336 Hemithyris, 182 Hemitrypa, 195 Hermit-crab, 328 Heteractinellida, 44 Heterocoenia, 98 Heterodont, 203, 219, 230 Heterogenetic homceomorphy, 14, 167, 270 Heteromyaria, 210 Heteropoda, 232, 248, 254 Heteropora, 195 INDEX 379 Hexacrinus, 145 Hexactinellida, 38-40, 47 Hildoceras, 276 Hinge (Brachiopoda), 162 ,, (Lamellibranchia), 203 Hinge-line (Brachiopoda), 162 ,, (Lamellibranchia), 203 Hinge-plate, 204 Hinnites, 216 Hippochrenes, 245 Hippopodium, 212 Hippurites, 221 Hirudinasa, 158 Hoernesia, 231 Holaster, 131 Holcospongia, 45 Holeostephanus, 287 Holectypus, 129 Holmia, 304 Holocystis, 93 Holopcea, 254 HolopeUa, 254 Holostomatous, 235, 253 Holothuroidea, 135 Homalonotus, 305 Homceomorphy, 14, 167, 270 Homomya, 227 Hoplites, 278 Hoploparia, 330 Horiostoma, 240 Hornera, 195 Horse, 13 Hughmilleria, 350 Hyalostelia, 38, 47 Hyboclypens, 129 Hybocrinus, 154 Hydra, 51, 52 Hydractinia, 53, 72 Hydrantb, 51 Hydrocaulus, 52 Hydrocorallina, 70 Hydrorhiza, 52 H}rdrospire, 152-154 Hydrotheca, 52, 56, 58 Hydrozoa, 51 Hymenocaris, 321 Hymenoptera, 337 Hyolithellus, 256 Hyolithes, 255, 256 Hypanthocrinus, 141 Hypostome, 296 Hypothyris, 182 Ichthyocrinus, 143 Idiostroma, 73 Idmonea, 192 Ilhemis, 306 Imperfection of the record, 12 Imperforate gasteropods, 235 Inarticulata, 162, 171-3 Incurrent canals, 33 Inferior lateral lobe, 267 Inflected lip, 235 Infra-basal plates, 139 Infusoria, 15 Inhalent canals, 33 Ink-sac, 259, 280, 283 Inner lip (Gasteropoda), 235 Inoceramus, 213 Insecta, 333 Integripalliata, 210 Inter-ambulacral area, 118, 124 ,, ,, plates, 118, 140 Inter-ambulacrum = inter-ambula- cral area, 118 Inter-brachial area, 113 ,, ,, plates, 140 Lnter-radial plates, 139 Iphidea, 170, 186 Iron pyrites, 7, 35, 56, 60 Irregularia (echinoids), 128 Isastrcea, 92 Ischadites, 47 Ms, 94, 103 Isocardia, 219 Isocrinus, 145, 146 Isodont, 203, 215, 230 Isopleura, 237, 254 Isopoda, 325 Isotropic, 3, 35 Jaws (echinoid), 124 Jelly-fishes, 8, 50, 73 Kampecaris, 333 Keel (Ammonoidea), 269 King-crab, 338 Kingena, 187 Koninckia, 99 Koninckina, 187 Kreischeria, 354 Kutorgina, 174 Labechia, 73 Labial palps, 200 380 INDEX Labrum, 296 Lagena, 23 Lamellibranchia, 197-231 Laminarian zone, 185, 252 Lancet-plate, 151 Lapivorthura, 114 Lateral budding of corals, 80 teeth, 204 Leda, 211 Leeches, 158 Left valve (laniellibranch), 208 Leioceras, 287 Leiopteria, 214 Leiostoma, 255 Lepadocrinus, 148 Lepas, 316, 317 Leperditia, 314 Lepidaster, 112 Lepidesthes, 121 Lepidocentrus, 133 Lepidodiscus, 157 Lepidopleurtis, 238 Lepidoptera, 335 Lepisma, 334 Lepralia, 195 Leptama, 176 Leptograptus, 68 Leptoplastus , 305 Leptostraca, 319 Leucosolenia, 32 Lichas, 309 Ligament, 205 Lima, 216 Limatula, 216 Limncea, 250 Limonite, 8 Limulus, 338-343 Lingual ribbon, 232 Lingula, 171 Lingulella, 171 Liomesus, 255 Liparoceras, 287 Litharcea, 93 Lithistida, 42, 47 Lithocampe, 29 Lithodomus, 212 Lithophagus, 212 Lithostrotion, 89 Littoral zone, 185, 252 Littorina, 242 Lituola, 23 Lobes (Ammonoidea), 267 Lobsters, 327 Locustidae, 335 Loganograptus, 67 Lofr^o, 286 Lonsdaleia, 90 Lophophore, 188, 191 Loricula, 317 Lotorium= Tritonium, 245 Loxonema, 241 Lucina, 223 Ludivigia, 287 Lung-books, 289, 352 Lunule, 202, 205 Lunulites, 195 Lyopomata, 170 Lytoceras, 273 Maclurea, 254 Macrocephalites, 277 Macrocheilus, 241 Macrochilina, 241 Macrocy Stella, 149 Macrodon= Grammatodon, 231 Macroscaphites, 274 Macrura, 329 Mactra, 225 Maculae, 296 Madrepora, 102, 104 Madreporaria, 77 Madreporic plate, 108, 112, 113, 125 Madreporite, 108, 147 Magas, 187 Magellania, 183 Malacostraca, 317 Malaptera, 254 Mamelon, 121 Mandibles, 290, 299, 312, 314, 316, 320, 328, 332, 333 Mantellum, 216 Mantle (Brachiopoda), 160 ,, (Cephalopoda), 258 ,, (Gasteropoda), 232 ,, (Lamellibranchia), 197 ,, (Mollusca), 196 ,, (Scaphopoda), 256 Mantle-cavity, 160, 197, 258 Marginal fasciole, 123 ,, plates, 108 ,, pores, 152 Marsipiocrinus, 145 Marsupites, 143 INDEX 381 Martinia, 179 Massive corals, 81 Mastigophora, 15 Maxillae, 290, 299, 312, 314, 316, 320, 328, 332, 333 Maxillipedes, 318, 324, 325, 326, 327, 328 May-flies, 335 Mecochirus, 332 Medlicottia, 287 Medusa, 51 Medusina, 73 Medusites, 73 Megalodon, 219 Megalosphere, 19 Megascleres, 35, 45 Melanatria, 255 Melania, 243 Melanopsis, 255 MeloTiechinus, 125 Melonites, 125 Membranipora, 194 Meretrix, 224 Meristina, 180 Merostomata, 338 Mesenteries, 74, 75, 76, 93 Mesoblastus, loo Mesonacis, 304 Mesopores, 192 Mesosoma, 337, 339, 340, 345, 352 Metasepta, 84, 85 Metasoma, 337, 339, 340, 345, 352 Metastoma, 296, 346, 347 Metopaster, 111 Metoptoma, 254 Meyeria, 329 Michelinia, 99 Micrabacia, 93 Micraster, 132 Microdiscus, 303 Micropora, 194 Microscleres, 35, 41, 45 Microsphere, 19 Microthyris, 183 Miliola, 20 Miliolina, 22 Millepora, 71, 72 Milleporidium, 71 Millericrinus, 144 Millestroma, 71 Millipedes, 332 Mimoceras, 271 Mites, 354 .17 (7 ™, 247 Mitraster, 111 Modiola, 212 Modiolopsis, 212 Mollusca, 19H-287 Monaxonida, 40, 46 Monocyclic, 139, 140 Monograptus, 69 Monomyaria, 200, 202, 209 Monophyllites, 287 Monoprionidian =uniserial, 58 Monotis, 231 Monticulipora, 193 MontUvaltia, 92 Mosquitoes, 336 Moths, 335 Multilocular Foraminifera, 17 Multispiral operculum, 236 Murchisonia, 239 Murex, 246 Muscular impressions, 165, 202, 261 Jl/?/a, 225 Mijalina, 212 Myacites, see Pleuromya, Homo- mya Myoconcha, 212 Hyophoria, 217 Myriapoda, 332 My sis, 324 Mytilus, 212 Myxospongida, 40 Nacreous layer, 206 Naiadites, 230 Nassa, 245 ZVaifcr/, 242 Naticopsis, 254 Nauplius larva, 291, 318 Nautiloidea, 260, 285 Nautilus, 260, 265, 285 Nebalia, 319 Neck-furrow, 293 Neck-ring, 293 Necrocarcinus, 331 Necrogammarus, 326 Necroscylla, 327 Neithea, 216 Nemagraptus, 68 Nematocysts, 50, 55 Nematophores, 55 382 INDEX Neolimulus, 342 Neotremata, 172 Neptunea, 246 Nerinea, 243 Nerita, 241 Neritina, 241 Neuroptera, 335 Niobe, 311 Nod os a Ha, 23 Notonectidae, 336 Nucleolites, 130 Nucleus (Protozoa), 15 ,, of operculum, 236 Nucula, 210 Nucuhuia, 211 Nudibranchia, 248 Nullipore zone, 185, 253 Nummulites, 25 Nummulitic Limestone, 27 Nyctiphanes, 324 Obelia, 53 Obolella, 171 Octactinellida, 44 Octopoda, 284 Octopus, 279, 284 Ocular j:>lates, 117 Oculina, 104 Odonata, 335 Odontochlle, 307 Odontophore, 197, 232, 259 Ogygia, 306 Olcostephanus, 287 Olenelloides, 304 Olenellus, 304 Olenus, 305 Oligocbseta, 158 Oligoporus, 121 OmphalophyUia, 104 Omphalotrochus, 240 Omphyma, 89 On I sens, 325 Ontogeny, 13, 167, 270 Onychocella, 195 Onychophora, 289 Ooecium, 190 Operculina, 26 Operculum, 236, 340 Ophidioceras, 287 Ophileta, 254 Ophiocten, 115 Opliioglypha, 114, 115 Ophiolepis, 115 Ophiura, 114, 115 Opbiuroidea, 112-115 Opilionina, 354 O^'s, 220 Opisthobranchia, 248, 254 Oral plates, 140 ,, surface, 108 Orbieuloidea, 173 Orbitoides, 26 Orbitolina, 23 Orbitolites, 22 Orbitremites, 155 Orbulina, 24 Order, 13 Organ-pipe coral, 94, 103 Omithella, 183 Orophocrinus, 150, 155 Cb-to, 177 Ortlwceras, 263 Orthoptera, 335 Orthothetes, 177 Osculum, 31 Ostracoda, 313 OsZrea, 216 Outer lip (Gasteropoda), 235 Outer-side-plate, 154 Oxyclymenia, 271 Oxynoticeras, 275 Oxytoma, 214 Oxyuropoda, 325 Pachastrella, 36, 42 Pachinion, 42 Pachydiscus, 287 Pachypora, 99 Pachyrisma, 219 Palceaster, 110 Palceasterina, 110 Palceechinus, 125 Palcega, 326 Palceinaclnis, 332 Palceocardita, 231 Palaocaris, 323 PaliBocoma, 111 Palaocorystes, 331 Palceoctopus, 284 Palaodiscus, 133 Palcsoneilo, 231 Palaontina, 335 Palaopalcemon, 325 Palccophonus, 353 INDEX 383 Pali, 79 Pallial line, 203 „ sinus, 203, 224, 226 Palp (mandibular), 320 PahuUna, 243 Panopea, 226 Panorpidae, 335 Paper-nautilus, 257, 279 Parabolina, 305 Parabolinella, 305 Paradox ides, 303 Parakoplites, 287 Parallel modification, 14, 66 Pqranebalia, 319 Parapodia, 158 Parasmilia, 92 Parkeria, 53 Parkinsonia, 278 Patella, 238 Paterina, 170 Pattonia, 333 Paucispiral operculum, 236 Pavonaria, 103 Pearly layer, 206 Pecten, 215, 216 Pectini-rhombs, 149 Pectines, 347, 352 Pectunculus, 211 Pedicellariaa, 109, 112, 122 Pedipalp, 337, 352 Pedipalpi, 354 Peduncle, 163 Peduncle-opening, 164 Pelagia, 73 Pelagic animals, 9, 249 Pelanechinus, 121 Pelecypoda, 197 Pelmatozoa, 136-157 Peltastes, 126 Peltoceras, 278 Peltura, 305 Pemphix, 332 Pen (squids), 280 Pennatula, 96 Pentacrinus, 143 Pentagonaster, 112 Pentamerus, 178 Pentremites, 149, 155 Perforata, 86, 93 Perforate gasteropols, 235 Periderm, 56, 59 Perignathic girdle, 124, 129 Periostracum, 207 Peripatus, 289 Peripetalous fasciole, 123 Periproct, 116 Perisarc, 52, 56 Periechocrinus, 145 Perischodomas, 133 Perisphhictes, 211 Peristome, 123, 235 Perna, 213 Peronella =Pcronidellai 45 Peronidelhi, 45 Petaloid ambulacra, 120 Petrifaction, 7 Phacops, 307 Phalangidea, 354 Phasianella, 240 Pbasmidffi, 335 Phillipsastrcea, 88 Phillipsia, 310 Pholadomya, 227 P/wfa.5, 226 Phormosella, 39, 47 Phormosoma, 121 Phorus, 242 Phragmoceras, 264 Phragmocone, 282 Phragmoteuthis, 286 Pbryganeidae, 335 Phrynus, 354 Phylactolaema, 191 Phyllocarida, 319 Phylloceras, 273 Phyllocainia, 104 Phyllograptus, 67 Phyllopoda, 312 Phylogeny, 12, 13, 65, 270 Phylum, 13 Phymosoma, 128 Piloceras, 286 Pinacoceras, 287 Pt/ma, 213 Pinnatopora, 195 Pinnules, 139 Pisania, 255 Pisocrinux, 145 Pitaria, 224 Placocystis, 149 Plagiostoma, 216 Planorbis, 250 Plant-lice, 336 Plasmopora, 101 384 INDEX Plastron (echinoids), 132 Platyceras, 242 Platychonia, 48 Platycrinus, 140 Platystrophia, 111 Pleopod, 318 Plesioteutliis, 286 Pleura, 297 Pleurocystis, 149 Pleurodictyum, 99 Pleurograptus, 68 Pleuromya, 227 Pleuronautilus, 287 Pleuropygia, 170 Pleurotoma, 247 Pleurotomaria, 239 Plicatula, 215 Plocoscyphia, 40 Plumaster, 112 Plumularia, 55, 56, 63 Plumulites = Turrilepas, 317 Pneumatocyst, 65 Podocrates, 332 Podocyrtis, 29 Pollicipes, 317 Polychasta, 158 Polyp, 51, 57, 70, 77, 79, 81 Polypary, 56 Polypide, 189 Polyplacophora, 237 Polypora, 195 Polytremacis, 101 Polyzoa, 188-195 Porcellaneous Foraminifera, 16, 18, 20-22 Pore-rhornbs, 148 Porifera, 31-49 Porites, 102 Porosphcera, 46 Posidonomya, 214 Post-abdomen, 352 Posterior canal, 235 Potamides, 244 Potamomya, 231 Poterioceras, 265 Poteriocrinas, 143 Prceanaspides, 323 Pre-abdomen, 352 Prearcturus, 325 Prestioicliia, 342 Primary plates, 119 ,, septum, 78, 84 Primitia, 314 Priscochiton, 238 Prismatic layer, 168, 206 Proboscina, 195 Prodissoconch, 208 Productus, 175 Proetus, 310 Prographularia, 103 Prolecanites, 272 Pro-ostracum, 283 PropalcemoH, 332 Propora, 101 Proscorpias, 353 Prosobranchia, 233 Prosoma, 337, 339, 340, 343, 350 Prosopon, 332 Protaspis, 300 Protaster, 114 Protegulum, 170 Prothelyplionus, 354 Protocardia, 223 Protocaris, 313 Protoconcb, 263, 268, 282 Protocystis, 149 Protolimulus, 343 Protolycosa, 354 Protoplasm, 15, 28 Protopodite, 290 Protoschizodus, 231 Protospongia, 39 Protozoa, 15-30 Protractor muscle, 203 Protremata, 174 Provinces (Molluscan), 251 Proximal end, 57 Psajnmobia, 225 Pseudocrinus, 149 Pseudodeltidium, 164 Pseudodiadema, 127 Pseudomelania, 241 Pseudomoiwtis, 214 Pseudoniscus, 343 Pseudopodia, 15, 16, 17, 28 Pseudoscorpionida, 354 Psiloceras, 275 Pfma, 213 Pterinea, 214 Pterinopecten, 216 Pteronites, 214 Pteropod ooze, 249 Pteropoda, 232, 249, 254 Pterygotus, 349 INDEX 385 Ptilodictya, 195 Ptilograptus, 55 Ptychites, 287 Pugnax, 182 Pulmonary sacs, 270 Pulmonata, 250, 254 Purpura, 246 Purpurina, 254 Purpuroidea, 242 Pygaster, 129 Pygidium, 292, 297 Pygocephalus, 325 Py gurus, 134 Pyrula, 255 Quenstedtoceras, 287 Quiuquehculina, 22 Radial plates, 114, 139, 149 „ symmetry, 105 Eadiolaria, 28-30 Eadiolarian ooze, 29 Eadiole, 122 Badiolites, 222 Eadula, 232 Raphistoma, 254 Rastrites, 69 Ray, 107 Eecapitulation theory, 13 Receptaculites, 47 Eed coral, 94 Eeef corals, 102 Eeflected lip (Gasteropoda), 235 Eegularia (echinoids), 125 Remopleurides, 295 Reniera, 41, 47 Requienia, 221 Retiolites, 69 Eetractor muscles, 203 Rhabdomeson, 193 Rhabdophyllia, 104 Rhacophyllites, 287 Rhaphidonema , 46 Rhipidomella, 177 Rhizocrinus, 145 Rhizophyllum, 92 Rhizostoma, 73 Rhizostomites, 73 PJiodocrinus, 146 Rhynchonella, 181 Rhynchotreta, 182 Eight valve, 208 Rimella, 245 Rissoa, 255 Eoot (Crinoid), 137 Eoot-tuft of Sponges, 34, 38 Rostellaria, 244 Eostral plate, 327 Eostrum, 320 Rotalia, 24 Eugose corals, 83, 86, 88-92 Saccammina, 22, 27 Saccocoma, 146 Saddles (Ammonoidea), 267 Sageuocrinus, 144 Salenia, 126 Salterella, 256 Sanguinolites, 229 Sao, 311 Sarcodina, 16 S ax i cava, 226 ScaZa, 241 Scalaria, 241 Scalpellum, 317 Scaphella, 255 Scaphites, 279 Scaphopoda, 256 Scenella, 254 Schizaster, 132 Schizoblastus, 155 Schizodont, 203, 217, 230 Schizodus, 217 Schizophoria, 177 Schizopoda, 323 Schlcenbachia, 279 Schlotheimia, 275 Scorpionida, 350 Scorpion-flies, 335 Scrobicule, 122 ScuZda, 327 Scutum, 316 Scyphomedusa?, 73 Scyphozoa, 73 Scytalia, 36, 43 Sea-anemones, 50, 74, 75, 77 Sea-cucumbers, 135 Sea-lilies, 136 Sea-urchins, 115-135 Seliscothon, 36, 43 Sepm, 280, 283 Septa (Cephalopoda), 261 „ (Corals), 77, 79, 83 ,, (Foraminifera), 17, 18 386 INDEX Septal fossula, 78 necks, 262, 266 Serpula, 159 Sertularia, 55, 56, 63 Sessile eyes, 325, 326 Sicula, 57, 60, 61 Shrimps, 329 Side-plates, 152 Silica, 3, 7, 28, 34, 35 Silver-fish, 334 Simple ambulacra, 120 Sinistral gasteropods, 234 Sinupalliata, 210 Siphon, 199, 232 Siplwnia, 43 Siphonida, 210 Siphonostomatous, 235, 253 Siphonotreta, 172 Siphonozooids, 96 Siphuncle, 262, 266, 283 Skeletal-spicules, 35 Slimonia, 349 Smithia, 88 Solarium, 242 Solaster, 107, 112 Solen, 225 Solitary corals, 102 Spatangus, 118, 135 Species, 13 Sphcerexochus, 308 Spharophthalmus, 305 Sphcerospongia, 47 Spliceridites, 231 Spicules, 34-37, 94, 95 Spiders, 354 Spines (Echinoidea), 122 Spiracles, 151, 154 Spiral angle, 233 „ ornament, 237 Spire of gasteropods, 233 Spirifer, 179 Spiriferina, 179 Spiroloculina, 22 Spiropora, 195 Spirorbis, 159 Spirula, 280, 284 Spirulirostra, 283, 286 Spondyhis, 215 Sponges, 31-49 Spongilla, 41, 46, 48 Spongin, 34, 40, 41, 45 Sporozoa, 16 Squid, 257 Squilla, 327 Stalked eyes, 327 Starfishes, 107 Staiirocephalus , 308 Stauronema, 48 Steganoblastus, 157 Stem (Blastoidea), 149 „ (Crinoidea), 136, 137 „ (Cystidea), 146 Stenotheca, 254 Stephanoceras, 276 Stepheoceras, 276 Sternum, 290, 346, 352 Stigmata, 352 Stomatopoda, 327 Stomatopora, 192 Stomechinus, 127 Stornodaeum, 75, 76, 94 Stone-canal, 110, 135 Strabops, 350 Straparollina, 254 Streptelasma, 91 Streptoneura, 233, 238 Strickland ia, 178 Stringoceplialus, 184 Stromatocystis, 157 Stromatopora, 71 Stromatoporella, 73 Stromatoporoidea, 71 Strombus, 244 Strophalosia, 175 Strophomena, 176 Strophonella, 176 Sty laster, 71 Styliform columella, 78 Stijlina, 92 Shjliola, 250 Stylomtrus, 349 Sub-anal fasciole, 123 Sub-petaloid ambulacra, 120 Sucking-discs, 257, 279, 281, 283 Superior lateral lobe, 267 Supplemental skeleton, 19, 25 Sur-anal plate, 118 Suture (Cephalopoda), 262, 267 ,, (Gasteropoda), 233 Sycum, 255 Synapta, 135 Synapticula, 79 Syncarida, 323 Syncyclonema, 215 INDEX 387 Syrhigopora, 98 Syringothyris, 179 Tabula, 79, 80, 95 Tail fin, 329 Talitrus, 326 Tanaidacea, 318 Taxocrinus, 145 Taxodont, 203, 210, 229 Tealliocaris, 325 Tectibrauchia, 249 Teeth (Brachiopoda), 162 ,, (Larnellibranch), 203 Tegmen, 137, 140 Tellina, 224 Telotremata, 179 Telson, 291, 312, 318, 320 Temnechinus, 135 Temnocheilus, 265, 287 Tentacles, 51, 75, 76, 93, 135, 137, 188, 232, 257, 260 Tentaculites, 255, 256 Terebratella, 183 Terebratula, 182 Terebratulina, 183 Teredo, 226 Tergum, 290, 316, 346, 352 Terrnitidge, 335 Testicardines, 170 Tetrabranchia, 260 Tetracoralla, 86 Tetractinellida, 41, 46 Tetragraptus, 67 Textularia, 23 Thamnastrcea, 93 Thamniscus, 195 Theca, 256 Theca (Corals), 77, 79 Thecidea, 174, 187 Thecosmilia, 93 Theonoa, 192 Thetironia, 224 Thetis, 224 Tholiasterella, 44, 48 Thorax (Trilobite), 292, 296 Thracia, 227 Ticks, 354 Titijus, 353 Tornoceras, 287 Toucasia, 221 Trabeculate columella, 79 Tracheae, 289, 332, 333 Trachyceras, 272 Transverse ornament, 237 Trepostomata, 192 Tretenterata, 170 Triarthrus, 296, 298 Tririd spicules, 42 Trigeminal, 120 Trigonia, 217 Triiobita, 292 Trlmerocephalus, 307 Trinucleus, 303 Tritaxia, 17 Tritonium, 245 Tritonofusus, 255 Trochiform gasteropods, 236 Trochoceras, 286 Trochocyathus, 102, 104 Trochodiscus, 29 Trochus, 240 Troostocrinus, 154, 155 Trophon, 255 Tube-feet, 108, 110, 112, 113, 115, 119, 135, 137, 157 Tubercles, 121 Tubipora, 94, 97, 98, 103 Tubular ia, 53 Turbinate gasteropods, 236 Turbinolia, 92 Turbo, 240 Turreted gasteropods, 236 Turrilepas, 317 Turrilites, 274 Turritella, 243 Ti/^is, 246 Ubaghsia, 99 Uintacrinus, 146 Umbilicus, 234 Umbo, 162, 202 Uncinulus, 182 Uncites, 180 Unguiculate operculum, 236 Unicardium, 223 Unigeminal, 120 Unilocular, 17 ZJm'o, 218 Uniramous, 318, 328 Uniserial crinoids, 139 ,, graptolites, 58 Univalve, 233 Urasterella, 112 Uronectes, 323 388 INDEX Uropod, 318 Valves (Brachiopod), 160, 161 „ (Lameliibranch), 197, 201, 208 Varices, 237 Varieties, 14 Velum, 52 Venericardia, 220 Ventral, 108, 201 Ventriculites, 39 Venus, 224 Vermetus, 233 Verrucoccelia, 48 Verrucosa, 317 Verruculina, 42 Vesicular tissue (corals), 79 Vestinautilus, 265 Vibracula, 190, 194 Virgula, 56, 60 Visceral chamber, 77 Vitreous Foraminifera, 16, 23, 26 Viviparus, 243 Volborthella, 255, 285 Voluta, 247 Volutospina, 247 Waldheirnia, 183 Wasps, 337 Water-bugs, 336 Water-vascular system, 105, 109, 115, 124 Whip-scorpions, 354 White ants, 335 Whorl, 233 Wilsonia, 182 Wood-louse, 325 Woodocrinus, 143 Worms, 158 Xanthopsis, 331 Xenophora, 242 Xiphosura, 338 Xiphoteuthis, 287 Xylobius, 333 Zaphrentis, 90 Zeilleria, 183 ZoEea, 291, 318 Zoantharia, 76-93 Zoarium, 188 Zone of Brachiopods and Corals, 185, 253 ,, of Nullipores, 185, 253 Zones (stratigraphical), 8 ,, of depth, 252 Zocecium, 189 Zoospore, 20 CAMBRIDGE : PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS. CAMBRIDGE BIOLOGICAL SERIES The Elements of Botany. By Sir Francis Darwin, Sc.D., M.B., F.R.S., Fellow of Christ's College. Second edition. Crown 8vo. With 94 illustrations. 4s. 6d. Lancet. This volume contains the substance of the course of lectures on botany given to medical students at Cambridge, and is as far as possible meant to meet the requirements of the first examination for the M.B. degree at that University. The plan of the book is to teach general principles and illustrate them by suitable examples, those being chosen as far as possible which fit in with the object of the book. In this way, the general principles being learnt, the student can apply them to other examples which cannot be included in this work, and so further extend his knowledge The book is well printed, easy to read, and the diagrams are clear ; it should prove a valuable work for those commencing the subject. Practical Physiology of Plants. By Sir Francis Darwin, Sc.D., F.R.S., and E. 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The Classification of Flowering Plants. By Alfred Barton Rendle, M.A. (Cantab.), D.Sc. (Lond.), F.L.S., Keeper of the Department of Botany, British Museum. Vol. I. Gymno- sperms and Monocotyledons. Demy 8vo. With 187 illustrations. 10s. 6d. net. Gardener's Chronicle. Numerous illustrations and an excellent index add to the value of the work. We heartily congratulate the author on the partial accomplishment of a difficult and laborious task. The part before us does but whet our appetite for what is to follow. The Origin and Influence of the Thorough-bred Horse. By W. Ridgeway, Sc.D., F.B.A., Disney Professor of Archaeology and Fellow of Gonville and Caius College. Demy 8vo. With 143 illustrations. \is. 6d. net. Westminster Gazette. There has never been a more learned contribution to equine literature than Professor Ridgeway's comprehensive and exhaustive book. Spectator. It would be difficult for Professor Ridgeway to write a book which did not contain at least one wholly novel thesis, and the present work is no exception to his practice. It is also an encyclopaedia of information on the history of the Equidae, collected from every source, from post- Pleiocene deposits to modern sporting newspapers. No detail escapes the author's industry, and... the result is a monument of sound learning, unique of its kind. Manual of Practical Morbid Anatomy, being a Hand- book for the Post-mortem Room. By H. D. Rolleston, M.A., M.D., F.R.C.P., and A. A. Kanthack, M.D., M.R.C.P. Crown 8vo. 6s. Cambridge Biological Series Fossil Plants : a text-book for students of Botany and Geology. By A. C. Seward, M.A., F.R.S., Professor of Botany in the University of Cambridge. In 3 vols. Demy 8vo. Vol. I. with a frontispiece and 11 1 illustrations. ior. net. Vol. II. with a frontispiece and 265 illustrations. 15^. net. [Vol. Ill in the Press. Revue Scientifique. 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Precisely the sort of book which, if it came into a thoughtful boy's hands, would turn him from a smatterer into a student.... One of the most instructive and attractive books that could be put into the hands of a young naturalist. Trees : A Handbook of Forest Botany for the Woodlands and the Laboratory. By H. Marshall Ward, Sc.D., F.R.S. Vol. I. Buds and Twigs. Vol. II. Leaves. Vol. III. Flowers and Inflorescences. Vol. IV. Fruits. Vol. V. Form and Habit, with an Appendix on Seedlings. Crown 8vo. With numerous illustrations. 4-r. 6d. net each. Arature. The clear and simple way in which the author treats the subject is sure to inspire many with interest and enthusiasm for the study of forest botany The work will be found indispensable to those students who wish to make an expert study of forest botany. 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The work is essentially suited to the requirements of those desirous of studying the grasses commonly grown in this country, and it can fairly be said that it furnishes an amount of information seldom obtained in more pretentious volumes. P. T. O. Cambridge Biological Series A Treatise on the British Freshwater Algae. By G. S. West, M.A., A.R.C.S., F.L.S., Lecturer in Botany in the University of Birmingham. Demy 8vo. [New edition in preparation A Manual and Dictionary of the Flowering Plants and Ferns. By J. C. Willis, M.A., Sc.D., Director of the Royal Botanic Gardens, Rio de Janeiro. Third edition. Crown 8vo. \os.bd. Field. Taking this handy volume and a local flora, the traveller or student may do an enormous amount of practical field work without any other botanical literature whatever The result is a work that ought to be included in every library of botany and horticulture or agriculture, and it is certainly one that the nomadic botanist cannot afford to leave at home.... 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