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STE Hk | nesting | PM iyi nh HW ‘ ty meet i { i POE R RODDED DD DD5 03505555555 555555 555551 1818 eke | itt} TUPUpT a eay feat! oa! | ‘ Sires ; popettht ; phys \ We) AA Miti4 ) jt. vv \ th] j Hell at HY HE! | ' Hit \; Anes ASF, pet Frederick Warne & Co.’s Publications THE LIBRARY OF NATURAL HISTORY 7 ROMANCE. The Romance of Wild Flowers. A Companion to the British Flora. By Edward Step, F.L.S., author of ‘Favourite Flowers of Garden and Greenhouse,” “‘ Wayside and Woodland Blossoms,” &c. In crown 8vo, cloth gilt, gilt top, price 6s. This volume (No. 1) contains upwards of 200 Original Illustrations by M. E. Step, T’. Carreras, and the Author, of which 32 are full-page plates, finely printed in tints from photographs taken from Nature expressly for the work, Love of the country, which steadily grows upon our ever-increasing town populations since they have taken to cycling, is largely mixed up with an interest in the animal and vegetable life of moorland, wood, and seashore. To aid in the identification of these creatures there are numerous admirable Floras and Text-books, which give the structural details with brevity and technical precision. Unfortunately, such literature only encourages the enthusiast, whilst it repels all others. The Library of Natural History Romance is projected, not for the enthusiastic specialist, but for the others—the readers who do not want to be told that a certain organ or creature zs of such a shape, but why it is so formed. Structure will be indicated plainly, but the reason for that structure and its relation to the creature’s habits and mode of life will be brought out strongly. The volumes will really aim at imparting the most interesting facts of Natural History in the most interesting manner, to which end the pencil and the camera will be freely used to assist the pen. “No one is better qualified to write a popular book on the British flora than Mr. Edward Step. He is the guide, counsellor, and friend of every field club, and his knowledge, gained as it is from Nature herself rather than from the library or the class-room, is placed before the unscientific reader in just such a form as he or she can easily comprehend. Print, illustrations, and text are alike excellent, and this library should appeal to every lover of the country.’’—Pall Mall Gazette. Chandos House, Bedford Street, Strand, London Frederick Warne & Cos Publications HOW TO KNOW AND WHERE TO FIND THE WILD FLOWERS. Wayside and Woodland Blossoms. First and Second Series. Pocket Guides to the British Wild Flowers for the Country Rambler. By Edward Step, author of “Favourite Flowers of Garden and Greenhouse,’ &c. In pocket-book form, size 6% by 44. ins. in neat art linen gilt, limp binding, round corners, price 7s. 6d, each; or in best French morocco tuck, gilt edges, with expanding Pocket for Notes, Specimens, &c., price 10s. 6d. each. The purpose of these volumes is to assist a very large and increasing class of persons who possess a strong love of flowers, but to whom the ordinary “ Floras”’ are as books written in an unknown tongue. ‘The author’s aim has been to write a work that, whilst it satisfied the rambler who merely wishes to identify the flowers of his path, might also serve as a stepping-stone to the “ Floras” of Hooker, Bentham, and Boswell-Syme. Each volume contains over 120 coloured plates, por- traying about 156 species, drawn direct from nature ; among them representatives of all the best-known genera will be found. ‘Thereare also several black and white plates, and upwards of 400 species are clearly described in the text. Mr. Britten, writing of the First Series in Mature Notes, said—‘' Mr. Step has condensed the best observations into a small compass, and his little volume is greatly in advance of every previous undertaking. It will add very slightly to the bulk of the most restricted arrangement of luggage, and forms an admirable pocket companion for the lover of wild flowers. .. . In it the reader will find much to learn and very little to unlearn, and we know of no other that can be so unreservedly recommended to the tyro in British Botany.” ‘‘This is just the little book which every true lover of that particular phase of natural beauty—namely, wild flowers—delights to find in his pocket when rambling along country lanes. The delicately-tinted illustra- tions are absolutely true to their growing counterparts."’"—Lzverfool Mercury. “It is an excellent book, which will be welcomed alike by the more learned in flower lore and by the beginner who would be more fully versed in the evolutions of woodland and wayside life."—Shefield Datly Telegraph. Chandos House, Bedford Street, Strand, London Mest ae Library of Natural History meee. Romance petit - LIFE ee % > - ie Sk 4 oe i TO 7 BANDED SNAIL}; 8 TO 10 WRINKLED SNAIL: 11, 12 HEATH SNAIL $ 13 TO 15 POINTED SNAIL. ow, fo S(SHELL LIFE AN INTRODUCTION TO THE BRITISH MOLLUSCA BY POW AD SEP, E.S. goa AUTHOR OF **FAVOURITE FLOWERS OF GARDEN AND GREENHOUSE” ‘“WAYSIDE AND WOODLAND BLOSSOMS’’ ‘*>HE ROMANCE OF WILD FLOWERS” ETC. ETC. WITH UPWARDS OF SIX HUNDRED ILLUSTRATIONS LON DON Peek eK WARNE & CQ. AND NEW YORK I9OI [Adl Rights Reserved | je oe neva Gap HE object of this work is much the same as that which led to the writing of its companion volume The Romance of Wild Flowers—to awaken an interest in, and lead to a closer study of, the creatures de- scribed. Shells and their makers, of course, necessi- tated a different kind of treatment from that accorded to the wild flowers; but the author's plan of making his readers first acquainted with the outstanding characteristics of the prevailing types of structure as embodied in such familiar forms as the snail, the mussel, and the cuttle, will enable them to follow him throughout the further chapters. It is not pretended that this volume will enable the reader to determine the exact species of all the native mollusks that may come under his notice; but it is hoped he may get from it an intelligent idea of the sub-kingdom so far as it is represented in these islands, and may be assisted in discriminating between most of those commonly encountered in the woods and lanes, by the pond and stream, or along the seashore. Of the seven hundred and fifty species of Mollusca in- digenous in the British Islands and the EAI Seas, no less than six hundred and fifty s -been briefly described in these pages. 5 a4 wsoN | Vals pot as. BN i”) i 9094 ‘ Wii a2} 5 Ii 6 Preface shell - collector’s handbook that the volume is sent forth; rather to suggest the consideration of these creatures as living organisms, whose diversity of form and structure has intimate relation to their mode of life, the persecution of enemies, and other factors in the struggle for existence—though some of us are at times too apt to regard such differences as being dictated by the needs of the classifying naturalist. In accordance with this intention, so far as was compatible with the necessity for pro- ducing a volume of handy size, attention has been directed to those habits and external influences that may reasonably be considered to have brought about modifications of form and colour, protective resem- blanees, and so forth. A few words may be added as to the system upon which the Genera, Families, and Orders have been grouped (see Appendix). In this matter I have mainly followed the plan adopted by the Rev. A. H. Cooke, M.A., in his admirable “ Molluses” (Cambridge Natural History, vol. i.), which is likely to long remain the standard text-book. The reader who desires to enter upon the wider and deeper study of this branch of Nature will thus experience no diffi- culty in expanding his elementary acquaintance with our local fauna into a fuller knowledge of the Mollusca of the world. GONTENTS I. INTRODUCTORY Materials for the study of Mollusks close at hand— Garden Snail and its shell—Swan Mussel and Common Mussel—Common Sepia or Cuttle—Types of three principal classes of Shell-life Il. THE SHELL AND ITS FORMATION Shellfish a misnomer—Some Mollusks without shells— The primitive shell—Importance of the conical form to shore - dwellers — Form of shell determined by habit of Mollusk—Comparisons between the shells of shallow and deep water, rock and sand-——-The door of the shell—The Oyster a degenerate—Thin shelis of pelagic species—Thin- ness of fresh-water shells—Land-snails—Shells of Slugs and Cuttles undeveloped or absent Ill. FEEDING AND BREATHING Oyster, though headless, has a mouth—Bivalves all tongueless—Cuttles’ bird-like beak—The Snail’s wonderful tooth-ribbon, and thousands of teeth—Powerful gizzards— Lungs and gills—Air-breathers and water-breathers—The mollusean heart and cirenlation—Blood mostly colourless . IV. SEEING, HEARING AND SMELLING Sense organs of Mollusks differ from those of higher animals — Decentralisation of sense impressions — Local brains—Nerve-threads, commissures, and ganglia—Eyes and eye-spots—Stalked-eyes, internal eyes, and vanished eyes —-Evolution of the molluscan eye—The Argus-eyed Scallops —The Saddle-oyster’s sense of hearing—Otocysts and Otoliths—Sense of smell more important than sight or hearing—Whelk’s keen scent—Slug’s sense of locality —A strange form of nose—Sense of touch acute . PAGE 40 48 8 Contents V. NUT-SHELLS AND MUSSELS Bivalve shells—Nut-shells—The ‘‘ foot” of a burrower in eravel—How the valves are kept closed—Hinges, locking- teeth, and bands of muscle—Leda-shells—Long siphons denote a deep burrower—Microscopic food of bivalves— Saddle-oysters and their attachment-plug—Noah’s Ark— Dog-Cockle—Eared Limopsis—Common Mussel—Its value for food and bait—Gregarious—Its byssus, or mooring- ropes—Mussels as foreshore conservators—The legend of Bideford Bridge—Horse Mussels and their crab companion —Crenellas VI. OYSTERS AND SCALLOPS Tan Mussels and Pea-crab—The Oyster : its personality —The parent of millions—Their infantile activity and later laziness—‘‘ Natives ” and ‘‘ Green Oysters ”— Enemies of the Oyster—Scallops—Their flight through the sea— Purpose of the ribs and ‘“ears”—The Quin as butterfly of the sea—File-shells VII. HEART-COCKLE AND FRESH-WATER COCKLES Astarte-shells—Hinge-teeth and their relation to habit of Mollusk—Another reason for ribs—Burrowing feet— Iceland Cyprina—Heart - Cockle—Lucina and Hatchet- shells— Double-tooth— Urchin-shell—A strange attachment —Kelly-shells—Shell-collecting from fish stomachs : a big haul—Coin-shells and Crustaceans—A_ bivalve scavenger —The Weasel’s-eye : its strange use of shell—Fresh-water Cockles and their climbing ropes—Pea-shells—Fresh-water Mussels: their probable origin—British pearls and pearl fishery—Swan Mussels—The Zebra Mussel and its strange history . VIII. WEDGE-SHELLS, VENUS-SHELLS, AND COCKLES Tellins—Mud_ burrowers—Furrow-shells—W edge-shells with milled edges—Trough-shells—Cirece and Artemis— Smooth Venus, our most massive native—Toothed edges PAGE bol | fay | Contents not requisite—The Clam—F ood and money—Carpet-shells —The Pullet—Rock Venus—Rock-borers—Red Nose—A molluscan hedgehog—Various Cockles—Common Cockle IX. GAPERS, PIDDOCKS, AND SHIPWORMS Shells that will not shut—Sunset-shells—Old Maid, a mud dweller—Its remarkable siphons, always extended— Basket-shells—Otter-shells or ‘‘ Clumps ”—Eaten in Herm —Razors of sorts—Why the hinge is not central—Razors not so sharp as mussels—Saxicava—Flask-shell—Piddocks —How rocks are broken up—Multivalve shells—Paper Piddocks—W ood Piddock—Ship-worms—How wreckage is disposed of—Pandora—Lantern-shells—Skye Gaper X. TUSK-SHELLS, MAIL-SHELLS, AND LIMPETS Elephant’s - tusk—A_ connecting link—Mail-shells—A shell of plates—Tortoiseshell Limpets—Other Limpets— Common Limpet and its stronghold—How it adheres—Its excavating powers—Its homing habit—Blue-rayed Limpet : its two forms—Slit-limpets and Keyhole-limpets—Ormer or Sea Ear—Its perforated shell XI. TOP-SHELLS AND PHEASANT-SHELL Dolphin-shells—Umbilicus and operculum—Top-shells —Pheasant-shell—A tiny gem—Fresh-water Nerite—Prob- able origin from a marine form XII. NECKLACE-SHELLS AND WINKLES Violet Sea-snail and its egg-raft—Eyeless derelicts— Wentletraps or Staircase-shells—A forty-guinea shell— Aclis-shells—Necklace-shells and their strange egg-bands —How shells are reduced—Marsenia : a snail that is seen through—Protective resemblance — Velvet-shell — Bonnet Limpets — Hungarian Cap—Cup-and-Saucer Limpet— A quaint interior—Winkles—Dwarf Winkle and _ its resemblance to bladders of Fucus—Rough Winkle—Is it becoming a land-snail?—An object-lesson in evolution— Periwinkle—Chink-shells 144 199 IO Contents XIII. SPIRE-SHELLS AND MARSH-SNAILS Round-mouthed Snail—A_ sea-snail that has left the sea —Evidences of its origin—Its shell door—Its enemy, Drilus —Point-shell—Spire-shells—Rissoas and Hydrobias—Small and numerous — Fresh-water Winkles — Sentinel-shells— Belted shell—Marsh Snails or River Snails—Viviparous— Valve-shells XIV. COWRY AND PYRAMID-SHELLS Small Needle-whelk—‘ Shillifillies °—Horn-shells—The Reversed Horn—Obelisk-shell—Screw-shell or Auger—A snail that deliberately breaks its shell—Strange history of the Blind-shell—Pelican’s-foot—Cowries—Another object- lesson in sell-evolution—Margin - shell—Poached Ege— Protective ornamentation—European Cowry—Atlanta XV. WHELKS AND CONELETS Some toothless sea-snails—Polished Eulima—Of_ para- sitic descent—Urchin Snail—A strange habitat—Pyramid- shells by the score— The teeth of the Whelk family— Spindle-shells—Why a siphon is needed—Sting-winkles— Varices or growth lines: what they indicate—W hy oysters are scarce—The Purple and its dye—How it clings to wave- washed rocks—Its stony shell—How the Star-fish eats it out of house and home—Its singular egg-capsules—Dog- whelks—Despoilers of bait—Spindle-shells—Red Whelk or Buckie—White Whelk—Common Whelk—Varieties and monsters—Ege capsules—Keen scent—Money value of a Whelk ‘ fishery ”—Least Whelk—Conelets . XVI. SEA-SLUGS Darwin’s mistake about Sea-slugs—How shells have been discarded—Actzeon and Bubble-shells—Snail crushers —Canoe - shells — Blind burrowers — Shells hidden and thinned—Lobe - shell—Sea Hare—A reputed depilatory— Its colour changes—Its purple clouds—The true Sea-slugs —Pleurobranchus — How enemies are discouraged — The origin of foot-lobes—Crowned Runcina—Cerata and their functions—Sea Lemons—Resemblance to sponges—Sense- PAGE Contents organs and gill-leaves—Venus Slug mimics anemone— Crested Slug— Declined by fishes— Homberg’s Triton— Deveted to Deadman’s Fingers—Gulf-weed Slug—Carrying one’s liver outside — Bushy - backed Slug — Disguise a necessity—Crowned Sea-nymph—Marbled Slug—Plumed ‘Kolis—Mimies Sagartia—Alder’s Molis—Green Molis— Despised olis: a spectral slug—Embleton’s Aolis—A variety that has taken to fresh water—Other Molids— Crowned olis : an anemone eater—Hermeeas, Crimson and Green—Food and shelter combined—Alder’s Slug—Green Elysia—Falmouth Slug—Pteropods . XVII. POND-SNAILS Lung breathers—Stalked-eyes and sessile eyes—Herma- phrodites—Herald-shell—Mouse-eared Alexia—Little Ear- shell—Fresh-water Limpets—Great Pond-snail—A_ general feeder—Its development affected by size of pond—Marsh Limneea—Dwarfed Limniea: a wet-nurse for the Liver Fluke—The evolution of Sheep Rot—Tennyson and Nature —Smooth Pond-snail—Ear Pond-snail—Wandering Pond- snail — Glutinous Snail — Involute Snail— Flat - coils or Trumpet-snails—The Ram/’s-horn—A small snail in a large house—Twisted Trumpet -snail—Other Trumpet-snails— An American visitor—Bladder-snails—Moss Bladder-snail . XVIII. LAND-SLUGS AND GLASS-SNAILS Unpopular subjects—Not all Slugs are harmful—Slugs with shells and without—Carnivorous Slug—A foe to earth- worms — Great Grey Slug—Its liking for sculleries and dairies—A_ taste for cream and lamb—A taster of books— Tree Slug—Yellow Slug—Field Slug—A destroyer of seed- lings and (reputed) consumption cure —Smooth Slug— Keeled Slug—Small Black Slug — Glass-snail—Simroth’s theory of Slug origins—Draparnaud’s Snail—Cellar Snail —Garlic Snail—Other Glass-snails—Love darts XIX. LAND-SNAILS More Slugs—Large Black Slug—Fondness for fruit—A very mixed feeder—Dusky Slug—Garden Slug—Spotted Kerry Slug — Twenty-five Helices — Dwarf Snail — The es 267 306 [2 Contents reward of patient seeking—Rock Snail—Rounded Snail— Stone-turning and leaf-sifting—Beautiful Snail—Prickly Snail—A climber of trees and a parachutist—Plated Snail— Cheese Snail—A relic of the ancient forests—Lapidary Snail —Bristly Snail—Ruddy Snail—A weakness for strawberries —Silky Snail—Green Hairy Snail—Dusky Snail—Kentish Snail—Carthusian Snail—Copse Snail—Knew the way to the tap—Sandhill Snail—A probable alien—Banded Snail —Snail - showers—The flavour of Down mutton — Sheep- snails—Heath Snail— Wrinkled Snail— Theorising on a false basis — Pointed Snail — Brown - lipped Snail — Its wonderful variation— W hite-lipped Snail—Common Garden Snail—Comes home to roost—A pple Snail or Roman Snail— A reputed alien, but more probable autochthon—A pples or pot-lids—Its winter sleep—Its egg-laying—A chalky ege- shell—The Apple-snail’s first meal—The Good Samaritan of Shell-life—Bulins—Molluscan Dirty Dicks—Chrysalis- shells—Numerous but minute—Barred doors—Tree Snail —Door-shells—Mimicry of beech-buds—How the ridges are worn away—Slippery Moss-snail—Agate Snail—A_ blind, subterrranean ghoul—Amber Snails and more flukes—A remarkable seashore slug XX. CUTTLES The most highly-organised mollusks—Suckers and Ink- bags — How colour-changes are effected —The Common Octopus—The Curled Octopus—Eight-armed Cuttles and ten-armed Cuttles—Spirula—Fragile shells that cross the Atlantic ~Common Cuttle—‘‘ Cuttle-bone ”—Hectocotylus- arm—Derivation of word Cuttle—Eges in bunches—Pen- and-ink mollusks—Little Cuttle—Ross’ Cuttle—Common Squid—First-class bait—How to catch a Squid—A bsence of Squid “pens” on shore — Egg-mops — Marbled Squid— Flying Squids—Architeuthis, a monstrous Squid—Oceanic Cuttles—Evolution of the Cuttles’ shells APPENDIX A Classified List of British Mollusks Index to Popular Names . : : : : PAGE 343 401 413 LIST OF ILLUSTRATIONS PAGE PLATES Land Snails (Helix) Frontispicce Dog Cockle, Green Crenella, - Facing page 63 ete. J Great Scallop and Quin ,, Scallops, \ Astarte-shells, ete. J” Iceland Cyprina and) Heart-Cockle \ Zebra Mussel, x 99 Montagu-shells, ete.J Orb-shells and) 78 Pea-shells J ssa aed and | ‘i 120 urrow-shells J Wedge-shells and | 127 Trough-shells J 0” as Venus-shells and) 130 Sarpetshells J ~ ”* ~“ Cockles 139 Sunset-shells and \ 142 Piddock ) las a Mail-shells and \ 182 Limpets J oF, Ormer and \ 193 Blue-rayed LimpetJ | Necklace-shells and \ Top-shells and | ee : Pheasant-shell J Facing page204 pare Winkles 5 he Periwinkle and | 26 Chink-shells J Conelets and \ 938 Dog-whelks J Sea-slugs . : yg Se Sea-slugs . BS it Sea-slugs . 4 a se owe Fresh-water Snails . ,, 319 Land-slugs (Limaz). ,, 334 Slug-sh ells and \ 340 Glass-snails J Land-slugs (Arion) . ,, 345 Land-snatls (Helix) . 5, 351 Brown-lipped Snail . ., 363 White-lipped Snail . ,, 364 Common Garden Snail \ 266 and Apple Snail J” Chrysalis Snails and\ 374 Door-shells fe Cuttles Cuttles 383 398 ** The above full-page plates depict about 300 figures of Mollusks, the individual names of which will be found at the foot of each plate. 13 14 List of Llustrations TEXT ENGRAVINGS INTRODUCTORY Shell of Garden Snail Swan Mussel . Edible Mussel Soft parts of Swan eee (Anodonta) . 2 Young of Swan Mussel . Sepia THE SHELL AND ITS FORMATION Limpet Common Top . Painted Top . : Netted Dog-whelk . Wentletrap Sting-winkle . Pelican’s-foot . FEEDING AND BREATHING Beak of a Cuttle- fish (Sepia) Portions of the tongue of a Whelk, with a row of teeth ; Teeth of radulie of Chi. nea stagnalis, Ancylus fluviatilis,andSuccinea putris . Under surface of ape SEEING, HEARING, AND SMELLING . : NUT-SHELLS AND MUSSELS Common Nut-shell Interior of Nut-shell Hinge-teeth : Shining Nut-shell . Beaked Leda . Dwarf Leda Interior of Beaked ede shell Saddle- oyster, oder Side view of Saddle- oyster, showing mode of attachment. . tight side of Anomia, with shell removed Prickly variety of the Saddle-oyster : Noah’s Ark . : Milky Ark, interior Common Mussel (JZytilus edulis), closed and attached by the byssus Common Mussel, opened to show the various organs. : Common Horse Marseel Part of epidermis Tulip Horse Mussel Bean Horse Mussel Cross-cut Crenella . Marbled Crenella . Green Crenella, interior. Black Crenella OYSTERS AND SCALLOPS Fan Mussel Interior of Fan Museel. right valve . Oyster, with right ‘wales removed , : 60 61 61 62 63 66 List of LlMustrations 2 PAGE Hunchback Scallop 82 Variegated Scallop 83 Quin or Queen 84 Seven-rayed Scallop 85 Tiger Scallop . : -/ 85 Mottled Scallop, shell and animal . 86 Gaping File-shell 88 Heart File-shell 88 Fragile File-shell 89 Gaping File-shell 89 File-shell in its nest 90 Gaping File-shell, in- terior . 91 HEART - COCKLE AND FRESH-WATER COCKLE 92 Furrowed Astarte . 93 Furrowed Astarte, in- terior . : 93 Flat Astarte . 94 Iceland Cyprina 95 Interior of Cyprina 95 Heart-Cockle . ; 56 Beaks of Heart-Cockle . 96 Interior of Heart-Cockle 97 Northern Lucina 97 Globose Kelly-shell, sus- pended by byssus 2 tO Interior of Globose Kelly- shell . : . 102 Minute Kelly- Sel 2 LO2 Sealy Coin-shell + 103 Shining Coin-shell and enlarged hinge = 105 Convex Coin-shell . =pl05 Turton’s Weasel-eye, open and closed . . 106 Hinge-teeth, Spheriuim . 107 Horny Orb-shell . 108 Nut Orb-shell . 108 ’ Lake Orb-shell 4109 WEDGE - SHELLS, Rtiver Pea-shell Painter’s Mussel Pearl Mussels, showing pearl within the shell, and detached pearls Swan Mussel, end view. } Duck Mussel . Zebra Mussel . VENUS - SHELLS AND COCKLES Tellin, with foot and siphons extended Blunt Tellin Baltic Tellin . Thin Tellin Rough Tellin, interior White Furrow-shell Peppery Furrow-shell Hinge-plate of Peppery Furrow-shell : Banded Wedge-shell Polished Wedge-shell Elliptical Trough-shell . Cut Trough-shell Rayed Trough-shell Smooth Venus Little Circe - shell, terior . : : Little Circe - eae in- terior . Enlarged plan of ee of fee Circe-shell Rayed Artemis Interiorof Rayed Artemis Smooth Artemis Smooth Venus Interior of Smooth Venus Banded Venus Warty Venus. Warty Venus, interior . Striped Venus e€x- 16 List of Ilustrations PAGE PAGE Wavy Venus, exterior Wrinkled Rock-borer . 161 and interior : w se Arctic Rock-borer . « 162 Golden Carpet-shell . 135 Flask-shell, front view . 162 Banded Carpet-shell . 135 Flask-shell, side view . 162 Banded Seaton in- Flask-shell . é . 163 terior . ; . 136 Case of Flask-shell. . 163 Pullet Carpet- nelle . 136 Pholas in its burrow .._:164 Cross-cut Carpet-shell . 137 Right valve of Common Rock Venus . ‘ ; Lai Piddock : ; . 165 tock-borer (Petricola Portion of hinge-plate . 165 lithophaga) . : . 138 Dorsal shields. : . 166 Rough Cockle . 140 Common Piddock in ita Little Cockle . : . 140 ecll = : 66 Banded Cockle : . 141 White FPiddeck : » ley Common Cockle, interior 141 Little Piddock ‘ ~ 167 Paper Piddock , . 168 GAPERS, PIDDOCKS, AND Wood Piddock ; . 169 SHIP-WORMS : . 144 Ship-worm = aAe Blunt Gaper . . 145 Norwegian Ship-worm . 172 Hinge - teeth of Psa Pandora-shell . : is mobia . : 145 Left valve of Pandora . 173 Tellin-like Sunset- shill § 146 Thin Lantern-shell. $a%s Faroe Sunset-shell . p47 Papery Lantern-shell . 176 Hinge and cartilage pro- cess of Gapers . . 148 | TUSK-SHELLS, M AIL-SHELLS, Old Maid : : . 149 AND LIMPETS . ~ Ans Blunt Gaper . : . 150 Elephant’s Tusk-shell . 179 Basket-shell . 3 Selent Grooved Tusk-shell . 180 Interior of Basket-shell, Mail-shells . : Peel's 1! showing hinge-teeth . 151 Under-side of Chiton ad Pointed Basket-shell . 151 profile of head. » 182 Siphons of Newra . roe | Bristly Mail-shell . . 183 Oblong Otter-shell . . 158 Bordered Mail-shell . 185 Common Otter-shell —. 154 Smooth Mail-shell . . 185 Short Razor . : - 155 Marbled Mail-shell . 186 Smooth Short Razor . 155 Tortoiseshell Limpet . 186 Egeg-shell Razor. ~ 156 Common Limpet . . 188 Pod Razor. ‘ = Dy Blue-rayed Limpet . 193 Pod Razor, interior of Blue-rayed Limpet, older left valve. : . 158 specimen. : Oe Sword Razor . . 160 Keyhole Limpet . . 194 Wrinkled Rock-borer . 161 Punctured Limpet . . 194 List of Illustrations Punctured Limpet, from PAGE above . = 195 Common Slit- pee . 195 Rosy Slit-limpet -) 195 Ormer . 196 TOP-SHELLS AND PHEAS- ANT-SHELL . Head of Grey-top Operculum < Common Top-sheli . Grey Top-shell Painted Top Pheasant-shell Head of Phasianella Fresh-water Nerite NECKLACE-SHELLS AND WINKLES Violet Sea-snail with te float : Violet-snail and Heat sidé view Head of W Satleconn Common Wentletrap Glossy Aclis-shell . Egg-band of Natica tailors is Large Necklace- Hell Life aspect of VV. catena. Common Necklace-shell . Velvet-shell Hungarian Cap : Cup-and-Saucer Limpet, interior Single row of ech fh i radulaot Periwinkle 2 Animal of male Peri- winkle, with the shell removed Periwinkle Eggs of Periwinkle Pp Banded Chink-shell, 3anded Chink-shell, larged . E Pallid Chink- abel: Eggs and young of Pallid Chink-shell . SPIRE-SHELLS AND MARSH- SNAILS. en- 17 PAGE 226 » ‘226 . 227 coe ~ 228 Xound-mouthed Sail Latticed Spire-shell Thick-lipped Spire-shell. Laver Spire-shell Common Bithynia . Dun Sentinel . Dun Sentinel . White Belted-shell . River Snails Common River Snail Lister’s River Snail Common Valve-shell CowRy AND PYRAMID- SHELLS. ° Small Needle-w feliz Auger-shell Blind-shell Pelican’s foot . Pelican’s foot, from below Margin-shell, from above and below 229 . 2al 231 . 232 . 233 . 234 . 234 . 235 . 236 . 236 237 238 . 239 . 240 . 240 «DAY 242 . 243 Margin-shell and animal . 244 . 244 Poached Egg . Poached Egg-shell . Young shell of Cowry European Cowry, from above and below . European Cowry Atlanta peront 243 . 245 245 ~ 245 . 246 WHELKS AND CONELETS . Polished Eulima 248 249 18 List of Illustrations PAGE PAGE Conical Pyramid-shell . 250 Gulf-weed Slug. 287 Staircase Pyramid . . 251 ~~ Bushy-backed Slug. . 288 Sting-winkle . , 2D2 Plumed Kolis ; . 291 Ribbed Spindle- Hell .. 252 Dotted Aolis . : . 2a) Purple or Dog-winkle 255 Green Elysia . : . 301 Egg-capsules of the Black Limapontia . . 302 Purple. : 257 Clone. . ; : . 303 Netted Dog-whelk. 7 257 Shell of Limacina . . 304 Netted Dog-whelk . . 258 | Chopyramidata . . 305 Slender Spindle-shell 260 | Common Whelk . 262 | POND-SNAILS . . 306 Row of teeth of Gnenmene Least Herald- stall: . 307 Whelk : ; . 263 | Mouse-eared Alexia . 308 Opercula of Whelk, nor- Fresh-water Limpet . 309 mal form and double . 263 Part of a row of teeth Cluster of Ege-capsules . 263 from the radula of Least Whelk . : . 265 Fresh-water Limpet . 310 Seven-ribbed Conelet . 265 Portion of row of teeth Teeth of Bela. : 2 HS from radula of Great Red Conelet . : . 266 Pond-snail . : rr | Turreted Conelet . . 266 Great Pond-snail . . 312 Great Pond-snail . . ole SEA-SLUGS . = 267 Marsh Limnea ’ . 314 Actzeon-shell . : 271 Dwarfed Limnea . . 314 Blunt Bubble-shell. 271 Smooth Pond-snail . ol Canoe-shell . ; » 212 Ear Pond-snail : es Cylindrical Bubble- shell 212 Wandering Pond-snail . 317 Cylindrical Bubble-shell 273 Ram/’s-horn Snail . . 320 Southern Bubble-shell . 273 Ram’s-horn . eel Soft Bubble-shell 274 Whirlpool tee! . 322 Gizzard-plates of Acera . 275 Margined Trumpet . 323 Soft Bubble-shell » 210 Shining Trumpet . . 325 Lobe-shell e715) Fountain Bladder-snail . 325 Lobe-shell 276 Shell of Fountain Sea Hare. : F 2716 Bladder-snail . 325 Shell of Sea Hare . 276 Moss Bladder-snail + oo Spawn of Doris . 282 Young of Doris, with LAND-SLUGS AND GLASS- shell . : : . 282 SHELLS ; . 328 Red Doris ‘ : - 202 Shell-bearing Slug(7Z ee Hairy Sea Lemon . 1 288 cella haliotidea) . . 330 Crested Slug . : . 286 Great Slug. : . 332 List of Illustrations PAGE Shell of Great Slug . 333 Pellucid Glass-snail and shell Pete! Cellar-snail : . 340 Tawny Glass-snail . . 342 LAND-SNAILS . 343 Black Slug . 344 Lapidary Snail . 353 Kentish Snail . 356 Carthusian Snail 2 oo) Sandhill Snail . 208 Pointed Snail. 302 Brown-lipped Snail 363 Mountain Bulin 370) Lesser Bulin 370 Large Chrysalis-snail 371 Pupa antivertigo 373 Tree Snail : 373 Plaited Door-shell . 374 Two-lipped Door-shell Slippery Moss-snail Three - toothed snail Agate Snail Ainber Snail . Row of teeth of radula of Succinea putris Large Amber Snail Graceful Amber Snail CurtLEs Suckers of Cuttle Spirula peronti Common Cuttle Shell of Sepia. Pen of Little Cuttle Little Cuttle, upper-side Common Squid Pen of Common Squid Moss- . HE materials for beginning an acquaintance with the shell- bearing animals le almost at every back door. Should there be an untidy corner of the ry garden where empty flower-pots are stored, a water-butt, or old wood is stood—there, without search, you may surely find a few examples of the dingy and too common Garden Snail. Much as we may object to the presence of this Snail where there are choice or tender plants, we shall find it a very handy example if we desire to obtain knowledge respecting the class to which it belongs. All the Mollusca, it is true, do not agree in structure with the Snail, any more than they agree in external appearance, but we may well adopt it as one of the few general types of structure under which all the species may be classed. A description of a species that is accessible to all, and at least familiar by sight, should prove more generally acceptable than an illustration drawn from 21 22 Shell Life the sea, which to the mass of Britons is not always get-at-able: therefore we search slightly among the trailing ivy in the back-garden and pick up a rather shabby-looking shell. This is the portable house wherein is lodged the common Garden Snail, and when the shell has been washed by contact with the dripping leaves after a heavy summer shower, one may get an idea of its true colours. It has a yellowish ground, thickly overlaid with spots and bands of dark warm brown broken by irregular lines of lighter tint. The shell is packed with a solid jelly of greenish hue— the living creature that formed the hard shell by excretion from its outer surfaces, but at present it is without form, a mere jelly in a jelly-mould. Let us put this specimen into a saucer with a little tepid water, and see what effect it will have upon him. Here are just those conditions he likes best,— warmth and moisture,—and he immediately begins to emerge from his shell and assume a definite shape. His body is elongated, with a flat base and a rounded upper side, the front ending in a sort of head dis- tinguished by two pairs of what children designate “horns.” These tentacles, instead of having the character of horns, are exceedingly soft and mobile, readily shortened to escape injury, or even completely withdrawn into the head. The lower of these appendages are short, and curved towards the ground ; the upper ones are much longer and carry the eyes Shell of Garden Snail Introductory 25 at their extremities—they take an upward direction and are waved backwards and forwards for the purpose of receiving impressions. The shell is supported near the middle of this elongated body, and appears to be rather small for the accommodation of so large an inmate, though we have not yet seen the whole of the Snail. What we can now see extended is generally known as the foot —the locomotive organ of the Snail. Within the shell is a good deal more—the “visceral hump” con- taining most of the internal organs. By a series of muscular contractions the Snail glides along upon the sole of its foot, slime being poured out for the necessary lubrication of its path—the glistening silvery trail that often enables the irate gardener swiftly to avenge the loss of his choicest seedlings. The mouth of the creature, as will have been seen, is situated just below the smaller pair of tentacles, and is bounded by lips. Behind the upper lip is the horny, arched, and ribbed jaw which bites off and breaks down the food, which is then passed over a ribbon-like tongue, set in regular order with thousands of hook-hke teeth, which rasp it into minute frag- ments. It then, of course, finds its way to the crop and the stomach by way of the gullet, for, in spite of the Snail’s jelly-like, structureless appearance, it can boast of heart, liver, kidney, reproductive organs, and both nervous and muscular systems. With these items we have no immediate concern, for in this volume I do not propose to enter deeply into the anatomy of my subjects; but there is one point to which I must call attention. If we look at the mouth of the shell when the Snail is extended, we shall see 24 Shell Life that it is closely lined with a very soft material called the mantle. The name suggests that this organ invests the whole body of the Snail when it is with- drawn into the shell; it does this and more—the mantle is the immediate producer of the shell. The porcelain of our Snail’s shell is composed mainly of carbonate of lme, and a microscopical section reveals the fact that it 1s made up of three distinct layers, each formed separately by different portions of the mantle. The material is obtained from the tissues of the plants upon which the Snail feeds, and has been absorbed from the soil by the roots. It appears to be separated from the Snail’s blood as this circulates through the mantle, which has the power to pour it in a fluid state upon its outer surface. By exposure to the atmosphere the fluid lime mixed with animal matter hardens into shell. This animal matter is conchiolin, a substance not differing greatly from chitin, of which the hard parts of insects are con- structed. The calcareous particles appear to be held together by the animal matter, and the whole sets into a hard stony formation. When a portion of shell is soaked in a weak acid, the carbonate of lime is dis- solved and a very delicate gelatinous film is left. A similar result is obtained in the case of Whelk and Top-shells to which certain sea-anemones attach them- selves. The base of the anemone appears to pour out some acid which dissolves the lime and leaves only a soft papery shell-form behind. When the mollusk is dead and the empty shell is left exposed to the atmo- sphere, the animal matter soon perishes and leaves the shell without gloss and exceedingly brittle. All parts of the mantle have power to excrete one Introductory 25 or other layers of this shell, as is proved by the repair of breakages. Many an adult shell bears signs of earlier accidents, the fractures being always evident from the fact that the colour patterns of the original are not reproduced. It is only the edge of the mantle that can produce the colour and pattern, and this is the part that first makes all the additions to a grow- ing shell to allow room for the growth of the animal, whilst the other parts of the mantle merely strengthen this first layer by backing and thickening it. The upper layer therefore carries the pattern and colour, whilst the lowest layer is usually white and highly polished. Outside all there is a kind of animal varnish, protecting the shell from many injuries, and this is known sometimes as the epidermis, but more correctly as the periostracum. Sometimes the shelly matter assumes the crystalline condition, the carbonate of lime having taken the form of calcite or aragonite. The statement made above that the fluid shell-matter is poured out and moulded upon the external surface of the mantle is the modern view generally held, but some authorities agree with the late Dr. W. B. Carpenter, who held that it was secreted in the cells - and interstices of the outer membrane of the mantle, which was afterwards separated. The Snail breathes air, but its “lung” is merely a cavity opening directly on the surface of the animal and closed at will, in a manner corresponding to the opening and closing of our lips. Its inner walls are lined with a fine network of vessels through which the blood courses, absorbing oxygen from the moist air and giving off carbon. This simple form of lung is referred to as the Pulmonary Sac, and its external ? 26 Shell Life opening may be watched for just below the lip of the shell on the right-hand side. Each individual Garden Snail combines the func- tions of both sexes. When one reflects that every one of those Snails clustering under the ivy will probably produce numerous eggs, he ceases to wonder at the enormous number that contrives to survive in spite of the depredations of birds and gardeners. One hundred may be taken as the average number of its eggs, and these are deposited in cup-shaped hollows among herbage, and covered with a little loose earth. The young come forth with the same shape as their parents, carrying a tiny, glassy shell on their backs, and differ- ing only in size. They become adult in about a year, and live until about five years old. Late in autumn they retire in companies to dry nooks and corners, there to spend the winter, many of them attaching their shells to those of their neighbours, all closed by tough films which keep in some degree of warmth. The Snail is not the stupid senseless creature he is commonly thought to be. His entire body is very sensi- tive, and even when deprived of his eyes he can distinguish between light and darkness. His sense of locality is of a high order, for he has his favourite roosting place and invariably returns to it for his day’s rest after a night’s ering i geeel wanderings in search of food. As an example of a second class of shells and shell- makers, let us take either of the large Swan Mussels Introductory 27 | that live in fresh-water ponds and lakes, or the Edible Mussel of our seashores. These are so much alike in general structure, that either will serve our present purpose. Here the shell is .a&* a bivalve—that is, it is GQegw formed in two pieces (valves) which are hinged together by their upper edges. Having seen that the shell of the Snail was produced by the mantle, we shall not be surprised to find that the Swan Mussel’s mantle is in two parts corresponding with the valves of the shell. Within the two lobes of the mantle there are four plates or leaves of very delicate tissue— the gills—in two pairs. Between these again he the foot, the visceral mass, and the lips of the mouth. This creature, though it has a mouth, has no head, and it does not wander about in search of food, but lies partly embedded in the mud with the shell gaping slightly, and waits for its food to come to it. The gill-plates are covered with delicate filaments (cilia) like the gossamer of small spiders, and, appar- ently by the constant rhythmical movement of these, currents of water are drawn in, passed over and between the gills, where the blood circulating through their tissues absorbs the oxygen, whilst the microscopic forms of animal and plant life with which the waters abound are filtered out and passed to the lips. This being the method of their feeding, the bivalves lack the horny jaws and the tooth-studded ribbon such as we found in the Garden Snail. Occasionally examples of the Swan Mussel are found combining the functions Edible Mussel 28 Shell Life of both sexes, but as a rule in bivalves the sexes are in separate individuals. We have here several points of difference in struc- ture and habit be- tween the Garden Snail and theSwan Mussel; there is also a want of uniformity in the length of their lives, for our pres- ent subject attains a respectable old age varying from twenty to thirty years, and does not begin to pro- duce young until it is five years old. This difference of age may be at least partly ac- Soft parts of Swan Mussel (Anodonta) counted for by the a foot; b, mouth; ¢, lips; d, e, gills; f, vent; quiet sedentary g, mantle; h, siphon A life lved by the Swan Mussel, which has also probably brought about a condition of degeneration from a primitive form ; whilst the active Snail has no doubt advanced from that primitive condition. The evidences of this degeneration are to be found in the loss of head, eyes, masticatory apparatus, and reduced means of locomotion. One other dissimilarity between these two types Introductory 29 must be noted. We have seen that the Snail lays egos, and that when the young escape from these they resemble their parents in all respects other than size. The Swan Mussel retains its egos until they hatch, but the little creatures that emerge in no wise resemble the parent. They appear to represent an early ancestral condition of the species. They have a temporary two-valved shell with hooked tips, with which they cling to the fins and tails of fishes, leading a kind of parasitical existence for a time; and then they drop to the mud where a new and permanent shell grows within the valves of their cradle. This part of the Swan Mussel’s history may be dealt with more fully later. Our third type of structure must be sought in the sea, for it has neither land nor fresh-water repre- sentative. It is the Common Sepia, one of the Cuttles. Here there is no sign of an external shell, and the shape is altogether different from either of those we have already considered. The Sepia is quite symmetrical in form, with a distinct head surmounted by a crown of eight arms and two long clubbed tentacles. In the centre of this crown is the mouth, armed with a pair of horny jaws not greatly unlike the beak of a parrot, which they resemble in their action. Within the mouth there is a tooth- ribbon like that of the Snail, but it is comparatively small, because the principal work of disintegration of food is done by the jaws, and the Sepia’s digestive powers are of a superior order. The eyes are large Young of Swan Mussel 30 Shell Life and prominent, placed on the sides of the head below the arms. There is no external shell, but in the mantle there is the one familiarly known as “Cuttle-bone,” more especially to bird fanciers. This consists of a thin hard shield, filled with thin soft plates of porous hme. The Sepia can walk head downwards by the aid of its arms, whose inner surfaces are covered with powerful suckers ; it can also swim rapidly backwards by violently ejecting water from the gill-chamber through a tube called the funnel. The opening by which water is admitted to the pair of gills is in front below the arms. The sexes are distinct, and the young are produced from eggs attached in great clusters to seaweeds. These three creatures —the Garden Snail, the Swan Mussel, and the Sepia—stand as types of the three principal classes of mollusks with which we have to deal in the following pages; and we have so introduced them on the principle of pro- ceeding from the most generally known to the less known. Regarded from the point of view of the systematic naturalist, the Sepia, as the highest rm NEA Sepia Introductory ae type, should stand first, the Snail next, and the Swan Mussel last,—its structure being more primi- _ tive than that of the others, — but reversing this order we propose to deal first with the more simple forms. For the natural sequence of the British species, proceeding from the most highly organised to the lowest groups, the reader is referred to the Appendix. y JHE | SHELL AND ES = === ]=—ORMATION Bo : HE great group of animals briefly considered in the fol- lowing pages has been singu- larly unfortunate in the names that have been bestowed upon it. The majority of the creatures comprised in it have been described as Shell-jish by the non-scientific person, and as such associated with forms so dissimilar as crabs and lobsters, which resemble oysters and whelks only in the fact that they are noé fishes. On the other hand, when the great Cuvier was seeking a name for the entire class in which cuttles, snails, bivalves, and slugs are included, and wishing to indicate the soft, boneless character of their bodies, he selected the word Mollusea, derived from the Latin mollis, soft. But it is not a very distinctive name, for there are many soft boneless creatures not included in the group, and moreover the Romans used the name for a kind of nut with a soft shell. 32 The Shell and its Formation a We are, therefore, in the position of having no well- known name that will apply with anything approach- ing accuracy or distinctness, in the way, for example, that we denote beasts, birds, reptiles, and fishes ; and there does not appear to be any prospect of getting what we want. The naturalist is so used to the term mollusk that he is not lkely to seek or adopt another, and the layman is too conservative to give up so well-known and so inaccurate a name as Shell- fish. The reader will understand why the word “Shells” occupies a more important position in the title of this volume than the makers and wearers of those shells, and will not regard it as being due to sympathy with the early collectors and writers who regarded the shell as of chief importance, and the animal that secreted and lived in it as quite a secondary matter. _ In such a case accuracy is out of the question, for many of the creatures described in these pages have no apparent shell; a greater number have absolutely none when full-grown, though some of them begin life with a rudimentary shell which does not develop. But though the shell is not everything, it is so characteristic of the Mollusca as a class, that we are Justified in giving some consideration to it at the start. There is every reason for supposing that the primitive molluscan shell was not much unlike that which covers the Limpets to-day. Such a form gives great strength with but a small expenditure of material, and it is susceptible of modification in many directions. A number of species whose anatomy shows they are not intimately related, have retained this form of shell to the present day. In proof of this 34 Shell Life we need only refer to the native species of Acmca, Haliotis, Calyptrea, and Ancylus. For creatures living in shallow water along the seashores, exposed to frequent hammer- ing by the waves, such a form would be highly protective, as may be proved by watching the Limpets (Patella) on the rocks. Adhering tightly with the base of their bodies to the rock, and drawing down the edges of the shell by muscular contraction, the wave breaks upon the shell without harming or shifting it. In the case of the Limpet the shell is enlarged equally all round its edge, so that it fits accurately to the spot of rock the Limpet has chosen for a permanent resting-place. Even where the simple uncoiled form of shell has been departed from, there has in innumerable in- stances been a retention of the general external shape, that the minimum of resistance shall be offered to the waves. Take either of the common species of Top-shells that frequent the same situations as the Limpets: although the cone is here coiled several times upon an axis, the external shape is still that of a cone with an almost flat base. All our univalve shells will be found to be modifications of this type, in some making a low pyramid, in others drawn out to a proportionately great length. This diversity of form is, no doubt, determined by the habit of the mollusk and the situation it inhabits. For example, those Common Top The Shell and its Formation aR species that adhere to rocks in shallow water (Top, Purple, Winkle, Limpet), and are therefore subject to the rushing of water and the heavy beating of breakers, have their shells broad, smooth, and free from sculpturing that might catch the water and so result in the mollusk being swept from its hold. Closely related species that live on sandy or gravelly bottoms appear in many cases to find an advantage in angles and knobs; probably because, their foothold being precarious, when they are detached by waves their irregular surface prevents their being swept far from the spot. This difference is well illustrated by comparing the Common ‘Top with a closely allied species, the Painted Top, which occurs on sand, and has the surface of the shell broken up into a series of little knobs. The Netted Dog-whelk lives on sandy shores, and its shell has a similar surface, whilst the upper surface of the animal is dotted with dark spots that closely resemble grains of sand. The Common Wentletrap has a great number of flat plates standing out edgewise from each coil of the long shell. The very rugged character of the Sting Winkle’s house is obviously determined by similar reasons for utility; and, though much less rugged, the strong sculpturing of the Pelican’s-foot is clearly of the same order. How the character of the shell is modified by Netted Dog-whelk 36 one Wife changed habits in the creature that makes it, may be seen clearly in the case of the Blue-rayed Limpet (Helcion). In its young condition it should be sought on the broad fronds of the large tangles and_ oar - weed. The form of the thin shell well suits it for this situation, the frond float- Wentletrap i Sac currents Sting Winkle and the shell offering little opposition to the flow of the water. As the frond waves iridescent gleams play upon its purple-brown, and in order that the Blue-rayed Limpet may not be readily seen it bears upon its clear brown shell from three to six fine lines of bright blue radiating from the apex and giving an effect similar to that seen on the tangles. As it gets older this Limpet climbs down the stalk, where there is no iridescence, and finally is to be found among the root-like suckers by which the weed is attached to the rock. In such a situation there is more risk to the shell from the rush of stones, ete., at the lower level. The shell, in con- sequence, becomes much thickened, the edges are modified to fit it for adhering to the cylindrical stem instead of the plane surface of the frond, and as the blue lines would be an attraction rather than a disguise they are gradually obscured. The shell Pelican’s-foot The Shell and its Formation 45, has assumed the form known as the Smooth Limpet. Exotic species of Putella that live entirely upon floating seaweeds have their transparent shells like those of Helcion, but those that live upon rocks require thick shells to withstand the breakers. All the species to which we have just referred— with the exception of the Limpets—have the mouth of the shell accurately closed by a thin plate of shell or chitin. It is seen closing the orifice of the Wentletrap figured opposite, and on the end of the foot of the Sting Winkle beside it. It is known as the operculum, or cover, and at one time was con- sidered to be the other valve, bringing the univalves into close agreement with the bivalves. But a little consideration serves to show that the operculum is not part of the true shell, for it is not a product of the mantle, but of the foot. And this brings us to the consideration of the enormous difference between the shells of, say, the Oyster and the Whelk. In spite of the very high value, commercial and epicurean, that is set upon the Oyster, present-day knowledge all seems to point to the probability that he is a degenerate from the form of the ancestral mollusk, which almost certainly had a head and something approaching a masticatory apparatus. Whilst some of its de- scendants in successive generations went on im- proving the simple tent-like form of their shells, by twisting them into spirals, and developing their organs to fit them for lives of varied activity; others, finding that the sea was well provided with food, appeared to think that activity involved an unnecessary strain upon the organism. These simply 38 Shell Life attached themselves to rocks or weeds, or burrowed shghtly in sand or mud, and lay with their mouths open to receive such good things as might chance to fall in. They lay over on one side, the mantle became divided into two lobes, and consequently the shell moulded upon its surface was in two valves hinged together, the head was lost, though the toothless, tongueless mouth remained, hidden by the lobes of the mantle. That the general tendency of development was in the direction of improving upon the simple ancestral form is indicated by the fact that of the enormous number of distinct species known in a fossil or recent condition, only one-fifth are bi- valves, whilst three-fourths have a single shell. To get back to the adaptation of the shell to the conditions of life: pelagic or floating species have the shell reduced to a thin glassy consistency, serv- ing the double purpose of rendering them lght and transparent, the transparency preventing their easy detection by enemies who are likely to regard them instead as part of the jelly-fishes upon which such pelagic mollusks largely subsist. Some species that dwell in deep water out of the reach of surface convulsions have very thin shells also. At the other extreme some deep-water forms that have evidently been much sought after by the larger fishes for their food secrete very thick and solid shells that may be proof against the equally hard and stony palate-teeth of the fishes. In all the fresh-water forms it is evident there can be little need for thick and heavy shells, and as a matter of fact they are light and thin. Especially is this The Shell and its Formation 39 the case with the pond-snails, who probably find carbonate of lime not very plentiful in their little world, neither is it greatly needed as a protection. A strong shell is required by those land-snails whose habitat exposes them to the attacks of birds like the thrush, but it is essential that the shell should not be heavy. The carbonate of lime is in this case obtained from the plants upon which the snails feed, and it is therefore only to be expected that on chalky soils the snails should be exceedingly abundant, whilst in sandy districts they are rare or entirely absent. But it does not follow that on chalky soil the shells will be necessarily thick, Clausilia laminata, for example, plentiful in beech woods on the chalk, having a thin semi-transparent shell, apparently with little chalk in it. In the slugs of our gardens and hedgerows the shell has been reduced to a little shield covering the breathing organ, or to a few granules of lime beneath the mantle; whilst many of the Sea-slugs have found it an advantage not to develop the shell at all, though they are born with the nucleus of a shell like all other mollusks. A somewhat similar case to that of the terrestrial slugs, so far that is as the shell is concerned, will be found among the Cephalopods: the Sepia produces beneath its mantle the familiar “cuttle-bone,” in the Squid this is reduced to the long transparent “pen” of animal matter only, whilst in the Octopus the shell is represented by two little stylets in the substance of the mantle. dis Wy rH pi eiezs LTHOUGH it is not a part of my ) YS purpose to enter upon the anatomy } mA } and physiology of the Mollusca \ beyond what is necessary for an S understanding of the differences in form and habit of the various groups, there are certain points which are so char- acteristic of the class, or which distinguish the several orders, that some elementary reference to them is essential. But the reader whose interest at present extends only to external forms and coverings may, an it please him, for the present skip this chapter and return to it later. Though, as we have seen, the bivalves have probably retrograded so far from the prevailing type as to have lost their heads, these presumed degenerates have retained a mouth and a digestive system as being necessary to their continued existence. But though the mouth remains in these bivalves, it is little more than an opening to the 40 Feeding and Breathing AI gullet and the stomach; there are neither jaws, teeth, nor tongue. The absence or presence of a tongue has been found to be an important item in classification, and we find that some authors have divided the Mollusca into two unequal groups, the Tongue-bearers (Glossophora) and the Tongue- less (Aglossa), the Tongue-bearers including the Cuttles and the Univalves, the Bivalves constituting the Tongueless. It is in the Cuttles that we find the highest development of jaws for the purpose of biting off portions of food. ‘These are composed of chitin, formed much lke the beak of a parrot, and working much in the same fashion except that in the case of the Cuttle the upper jaw works within the lower. The more ordinary type of jaws may be observed by watching any of our common snails feeding. The Land-snails (felix) have the jaw only in one portion, and this is placed behind the upper lip; but in the Pond-snails (Zimnea) there is an accessory plate on either side of the mouth, and these act with the upper plate. If a pond- snail be watched as it glides up the glass of an aquarium and cleans off the minute vegetation, the mechanism of the jaws will be understood better than from a description. The food having been cut off by the jaws is not yet in a condition to be readily digested; it has first to be masticated. This work is performed Upper (a) and lower (l) portions of the beak of a Cuttle-fish (Sepia) 42 Shell Life by a very remarkable organ peculiar to the Mollusca. It is an almost transparent ribbon of chitin, whose upper surface bears a large number of minute teeth, of varying forms, number, and arrangement, set in transverse rows, and each row symmetrically divided into central, lateral, and marginal teeth. The organ is variously known as the tongue, the radula, the lingual ribbon, or the odontophore. Only a small portion is brought into action, the remainder AY m= aN ” being coiled away at the back of the ent nee mouth, ready for use when the teeth of a Whelk, with On the forepart shall have been worn ea Sec out. These teeth as a rule are few and large in those species of car- nivorous habit, whilst those of herbivorous tendency have them small and numerous. Many of the carnivorous mollusks make their tongues serve a double office, for they have no jaws, and the whole of the cutting and breaking up of their food has to be done by the teeth; this, no doubt, explains their larger size. The number of these teeth to one tongue or radula varies to a remarkable extent: thus, one of the Sea- slugs (olis coronata) of our own coasts has only about 17, whilst the large brown Sprinkled-snail (Helix aspersa) of our gardens and hedges has 105 teeth in each transverse row, and no less than 135 rows—that is, a total of 14,175 teeth in one mouth. There are, of course, many species with numbers intermediate between olis and Helix; the large Pond-snail (Limnea stagnalis), whose teeth are shown in the figure @ below, has 111 such teeth in E Ree Feeding and Breathing 43 a row and about 110 rows=12,210; the little Fresh- water Limpet (Ancylus fluviatilis) b has 120 rows of 75=9000; and the Amber Shell (Succinea putris) c of our watersides has 50 rows of 65 teeth =3250. A Mexican species of Helix is said to have 40,000 teeth, whilst Umbrella, a Mediterranean mollusk, has so many it is impossible to count them, but they have been estimated to number somewhere about 750,000! Every one of these minute teeth has DETAILER : SUOBRBOL RAMI ‘CN Teeth of radula of—a, Limnea stagnalis; b, Ancylus fluviatilis ; c, Succinea putris (greatly magnified) muscular attachment to the radula, and can be erected or depressed at the will of the mollusk. These remarkable organs extracted from the mouth of any of the common mollusks of our hedges or seashores, make beautiful objects for the microscope; but their preparation requires a good deal of care and nice manipulation. They are first boiled in caustic potash to get rid of the animal matter, and after washing in clean water are mounted in glycerine jelly. Most of the mollusks that bear these radule are also provided with salivary glands, and in some of the species that habitually bore through the shells 4A Shell Life of others in order to feed upon the occupant, the saliva is found to contain an appreciable proportion of free sulphuric acid, which evidently softens the spot of shell upon which the radula is then brought to bear. The mollusean stomach, with which we have not space to deal, varies with the habit and food of the mollusk. Some species have it lined with knife-like plates, or with knobs and teeth. The Canoe-shell (Scaphander lignarius) has a gizzard in which the Tusk-shell (Dentaliwm), its favourite food, is crushed up prior to digestion. Having glanced at the mechanism by which the mollusks prepare their food for assimilation, let us take a similarly brief and superficial view of the means whereby the blood is aérated in the principal groups. It is evident that one system of respiration will not serve for the whole of the Mollusca, seeing that whilst some spend their lives submerged in fresh or salt water, others live as constantly surrounded by the atmosphere. Many of the fresh-water species, however, breathe air only, and cannot therefore venture far from the surface, their air-chamber requiring to be frequently recharged. On the other hand, marine species like the Limpet and Periwinkle, provided with gills for breathing water, have to spend hours on the dry rocks, and can only do so by storing sufficient moisture to keep their gills damp. It is probable that the ancestral mollusk had no special organs for respiration, but simply absorbed oxygen through his surface tissues, beneath which the blood flowed and took up the vital gas. Then Feeding and Breathing 45 probably the production of a shell closely covered so much of the surface that a simple comb-like organ was developed to carry on this function constantly. Such an organ exists in what we may regard as little different from the primitive form in certain species of Mail-shells (Chiton). Into this comb-like organ (ctenidium) the blood flows, and through the tissues of the branches absorbs the oxygen from the surrounding waters. In other species these simple ctenidia have degenerated until no longer functional, and their place is taken more efficiently by a series of plate-lke gills encircling the body Such a form of res- piratory apparatus may be seen in the Limpet, of which a fivure is here given. Here the letters ¢ ¢ ¢ show the position of the encircling series of gill-plates, whilst the true but aborted ctenidia must be sought in a pair of very small yellow bodies situated on the sides of the neck. Under surface of Limpet External branchize a, foot; b, mantle; ¢, gills; d, mouth; are also developed in alas many of the Sea-slugs, taking the form of cerata, whip- like, plume-like, or foliage-like processes from the back, 46 Shell Life through which the blood flows and takes up oxygen through their tissues. In the bivalves, as will be more fully described later, the gills vary greatly in the degree of complexity. They are usually placed on either side of the body between it and the mantle which thus form the branchial cavity. In most cases a couple of tubes or siphons lead to this chamber from the exterior, one admitting fresh supplies of water, the other carrying off that which has passed over the gills and been robbed of its oxygen. In the land and fresh-water snails (excepting the few whose shells are closed by an operculum) respira- tion is effected in a “lung-chamber,” though there is no lung in the sense of a spongy mass of tubes as we know it in the higher animals. The chamber, which opens on the right side of the snail, more or less towards the front part, is lined with a network of branching vessels through which the blood circulates. Air is taken into this cavity frequently when the mollusk is active, and then the opening is closed until all the oxygen has been taken up by the blood, when the chamber is refilled and again closed. The Pond-snails (Linviea) when living in shallow water frequently come to the surface to recharge this cavity with fresh air, but when living at considerable depths they appear to absorb the oxygen from the water, whether by filling this lung-chamber or through the general skin-surface is not quite clear. In intimate relation with the varied forms of gills or lungs there is, of course, a heart; and where there is only a single gill there will only be one auricle and one ventricle to the heart, but there may be two or four auricles if there are as many gills. From the Feeding and Breathing 47 gills the oxygenated blood flows to the heart, whence by way of the aorta it is distributed throughout the body, and returning by veins it 1s again passed through the gills. It must not be supposed, however, that the circulation is as rigidly confined in definite tubular vessels as in the higher animals. Much of the blood appears to flow indefinitely in irregular spaces of the body called lacune and sinuses, getting reinforced by that which has passed through the gills and heart, but perhaps not all of it finding its way back to these organs. The vital fluid is in most mollusks colourless, but a few of the more active species possess the red colouring matter (hemoglobin) which distinguishes the blood of vertebrates, ft: sy aly il HW E AN aM a (en ra SME pS 2 = cee ‘ Niji ee | see Re od Ss “S$ we have just learned in the cases of respiration and circulation, we must not expect to find in the Mollusca organs of sense similar to those of the higher animals. The whole of the body being so soft is no doubt highly sensitive; nevertheless there are special organs for special senses, and these organs are well furnished with nerves to convey their im- pressions to the local brain. For there is no grand centre of the nervous system as furnished by our brain. Instead of one great trunk-line of nerves and nerve-bundles, as in the vertebrates, we find in the mollusks a system of large and small nerve-threads traversing the length and breadth of the animal, connected here and there by loops (commsswres), | and from -certain knots (local brains or ganglia) sending off a number of short branches. All these local brains are connected by other nerves, and the chief of them are known as the cerebral, the pedal, and 48 Seeing, Hearing, and Smelling 49 the visceral ganglia. In those mollusks that possess a distinct head nerves go off from the cerebral ganglion to the tentacles, the eyes, and are connected with a pair of small ganglia (the buccal gangha) that command all the mouth parts, the pedal ganglia supplies the foot, the visceral or pleural ganglia send nerves to the mantle, the heart, the gills, the stomach, and the other internal organs. The eyes of the Mollusca are alike different from those of higher animals, and from one another. The highest development of the molluscan eye is found among the Cuttle-fishes and their allies, but a pair of well-developed eyes is the possession of nearly all the mollusks that are furnished with heads. Yet the presence of a head is not absolutely essential for the acquirement of eyes, for some of the bivalves, such as the Seallops and Ark-shells, have eyes on the fringes of the mantle, and some foreign species of Mail-shells (Chiton) have been found to have certain parts of their shell-plates closely studded with minute pigmented dots which serve the office of eyes. In the land-snails the eyes are carried at the top of the longer pair of tentacles, a position which allows the snail to see in all directions; in the water-snails the eyes are at the base of the tentacles. Species that live underground have the eyes more or less aborted. Our own little Needle-shell (Cecilianella acicula), which lives an entirely subterranean life, has lost them altogether; so also have several of our marine- snails that are always seeking their food under the sand. Others of similar habit have eyes, but they are covered by thick skin that can allow very little impression of light to reach them. 50 Shell Life From a consideration of a series of molluscan eyes it is not difficult to surmise the developmental history of the most perfect among them. ‘Thus, in the Limpet—to which we have already referred as being probably much like the ancestral mollusk—there is little more than a fold of the skin forming a depres- sion lined with rod-shaped cells containing pigment and forming a retina, which is connected with the optic nerve. In the Tops (Z'rochus) the depression of the epidermis is greater, so that it encloses a spherical space lined with retinal cells and filled with fluid (vitreous humour), but open in front so that the face of the eye is bathed in water. In the Sting Winkles (/wrew) there is an advance upon this form, for the opening of the eye has become quite closed and there is a lens before the vitreous humour. Now the eyes of these three species present a very close resemblance to three stages in the development of the eye in the embryo of the Squid (Lolzgo), which shows an advance upon Murex by producing an iris round the fore-part of the lens, an optical chamber in front of the lens, and a transparent cornea before that again. It must be apparent that eyes are of the greatest value to the most active species of Mollusca—the Cuttles. These have, consequently, developed their eyes to a greater degree of efficiency than other orders. The inactive, often fixed, bivalves have been found in many cases to have a pair of eyes on what may be regarded as the head during their larval condition, thus indicating that in the early history of the Pelecypoda they had eyes in the adult state. Those bivalves that lead a more active life, such as Seeing, Hearing, and Smelling 51 the Scallops (Pecten), have a considerable develop- ment of eyes upon the fringes of the mantle, and it has been reasonably surmised that these eyes enable them to guide themselves in their vigorous zigzag flights through the waters. But it may be regarded as tolerably certain that these eye-substitutes, or pigment spots, that are crowded upon certain parts of the mantle in many bivalves are merely sensitive to varying qualities of light and are useless for observation. The casting of a shadow upon such species affects these pigment spots, and from them the intelligence is conveyed along the nerves to the various ganglia, with the result that as a precaution- ary measure, the foot and siphons are withdrawn and the valves are shut with a snap. The Land- snails (felix) being crepuscular or nocturnal in their habits can see farther in twilight than at midday, but their visual powers are very limited at the best, and extend only to a distance of about six millimetres. The Round-mouthed Snail (Cyclo- stoma elegans), however, whose eyes are not mounted on tentacles, can see to a distance of about a foot. The sense of hearing has not been very extensively investigated, at least little but negative results have been obtained from experiments made with a view to testing its extent. One experiment of the kind made by Mr. W. Bateson in the Plymouth Laboratory of the Marine Biological Association, a few years ago, showed that a Saddle-oyster (Anomia) sus- pended in the water to be free from any chance of jarring of the solidly-framed tank, closed its valves on Mr. Bateson making a creaking sound 52 Shell Life of a particular pitch by rubbing his finger along the glass. The seat of hearing resides in a pair of closed cells called otocysts filled with a clear fluid in which are suspended one or more grains of chalky material ealled otoliths, and lined with cilia. These otoliths may be very numerous, and they are agitated by sounds in the immediate neighbourhood of the animal. These vibrations act upon the cilia which convey impressions by the acoustic nerve to the cerebral or the pedal ganglia. The most important of the senses to the Mollusca is apparently that of smell. It is quite certain that it is much farther-reaching than either vision or hearing, and more constantly in use. Great numbers of carnivorous mollusks, such as whelks, dog-whelks, and naticas, are found in lobster-pots baited with “high” fish which they have smelled through the waters. Slugs appear to be highly endowed with this sense. Apples and bean-pods dropped in the centre of a road will draw slugs from the hedges on either side. As soon as certain species of Agaric come up in the woods slugs bear down upon them and commence feeding upon them. They are also able to locate a dish of milk in a dairy and proceed to drink from it. Of course, this sense is more highly developed in the active univalves than in the more or less sedentary bivalves, but the agile Pea-shells (Pisidiwm) are not deficient in it, as shown by the numbers that swarm over any dead animal that has been thrown into a ditch or pond inhabited by them. Some of the Sea-slugs have a special pair of antennz furnished with projecting plates which are believed Seeing, Hearing, and Smelling 53 to collect sensations of smell from the surrounding waters. They are therefore known as rhinophores or nose-bearers. The sense of touch is acute, as must be obvious to anyone who has handled almost any species of mollusk. Creatures of such soft substance must necessarily be very sensitive in this direction or they would meet with many injuries. To touch a snail, however lightly, is to cause it to shrink into its shell at once. A slug has no shell that it can crawl into on being molested, but it instantly draws in its eyes and antennz and hunches the body up into a thick, short heap that exposes the minimum of surface to attack. In many of the shelled species the margin of the mantle is cut up into lobes and filaments which are all very sensitive to touch, and in some there is in addition a pair of protruding palps near the mouth that serve as tactile organs. These palps are also present in the bivalves but there, except in special cases, most of the tactile work is performed by the foot and the siphons. oa eee = —— we Pre er Gi PN H K i" } I} TE wr ih2 B=. ow = Reins TT Ge =! ( ail Me Sa > Oe. . (ert Teun SS Se al Z ‘ fi G Tho = SELS = =, cs f = = h a A If Hine {} G . vy Ly 4 = i a lo -G Ab . ~~. — 5 ays 1% § Y different systems have been adopted at various times for the intelligent and orderly arrangement of the bivalve mollusks (Pelecy- = poda) That followed in these pages is based upon the character of the breathing organs, and, all things considered, this appears to afford the most natural basis. In the sketch of the Swan Mussel in the opening chapter the position and structure of these organs were briefly indicated, but in that species the gills have reached a high stage of development. Starting from the simplest form of such organs we find examples in the little Nut-shells that burrow in the mud and sand of our seashores. The most plentiful of these is the Common Nut- shell (Nucula nucleus), whose empty shells may be found along our beaches washed in from deeper bd Nut-shells and Mussels 55 water, its living range being between 3 and 145 fathoms of water. The shell, as shown in the figure, is bluntly triangular in shape, coloured outside with yellowish green marked with , darker growth-lnes running parallel with the lower margin, whilst many very fine grooves radiate from the rather prominent ,orre" beak to the lower margin. The little creature that produces this shell is cream coloured; its mantle has plain margins, and its oval foot is toothed all round the edge. The mouth and lps are small, but the lips have long appendages which are protruded from the shell at the same time as the foot, and used as sense-organs in the search for food. The small brown gills are simple and plume-like. The maker of the Nut-shell burrows among sand and gravel, the “foot” being extended to its utmost length and worked between the fragments; each tip of the tooth-like edges then catches hold of a particle of gravel, the foot as a whole is shortened, and so the shell is hauled along by the contraction of the foot. At the same time the appendages of the lips feel about for food. When the dredge has scraped up one of these little mollusks from the bottom there is no foot visible; it has been withdrawn into the shell, and the valves now fit closely together. ~ Only the insertion of a knife to sever the oS) muscles, or to break them by leverage, can Ku” effect the opening of the shell. The Interior of ~examination of an odd empty valve, Nut-shell picked up on the shore, or of the accom- panying figure, will help us to understand how this firm closure is maintained. It is a left-hand valve, 56 Shell Life so that the figure shows it in its natural position, with the concave side towards us. In the com- plete shell the upper margin of this valve is connected with its fellow by a kind of hinge (ligament), resembling those primitive leather hinges by which boys attach lids to boxes and doors to rabbit-hutches. This shell hinge, however, is more horny than leathery, and is, so to speak, fixed on the stretch, and this explains why when a bivalve mollusk dies its shell gapes open: the hinge-ligament exerts a pulling action which tends to separate the lower edges. Just beneath the beak inside each valve there is a little spoon-shaped projection containing a bulging bit of elastic cartilage, which also serves the on purpose of forcing the valves apart. On ™, either side of this cartilage is a row of low ae say ridges like the teeth of a comb, and into the spaces between similar teeth on the right valve fit; the lower margin of each valve is also faintly marked in a like manner. The number of the hinge-teeth varies in different species; in the present one there are about 15 teeth in front of the beak and about 25 behind it. The object of all these interlocking teeth is to ensure the accurate closing of the valves when they are brought together, and to prevent any lateral movement that would enable an enemy to destroy the hinge. But the mechanism by which the two valves are closed and held tightly _ together, in spite of the opening action of the hinge- ligament, consists of a couple of bands of muscle, one towards each end of the shell. On the pearly inner surface of the valve we can see slight oval impres- Nut-shells and Mussels G7 sions of the ends of these muscles; these are the points to which they were attached. The hinge-teeth on the valves of the Nut-shells are simple in character, but we shall find in other species that they gradually became more complex. There are three other native species of Nut-shells whose peculiarities may be briefly noted in contrast with those of the common species. The Furrowed Nut-shell (VW. sulcata) has a larger, more triangular shell, with five ridges parallel with the lower margin ; dull olive. Found locally in from 3 to 50 fathoms where the bottom is of sandy mud or clay. The Shining Nut-shell (V. netida) is more acutely tri- angular, yellowish brown, and very glossy; mantle fringed. Sand and gravel from extreme low water to 86 fathoms, but not very common. The Thin Nut-shell (WV. tenuis), though still triangular, has a tendency eae to roundness of outline, but flattened from side to side; brownish yellow, thin, and glossy. Found locally, in sand and mud from 25 to 100 fathoms, chiefly along the Scottish coasts, the north- east of England, and east and south of Ireland. The external colours given above are those of the living epidermis or periostracwm, which invests and protects the shell from the action of gases dissolved in the water. Beneath this covering the actual surface of the shell may be entirely different in hue, but where the epidermis is permanent it will be more convenient to indicate its colour rather than that of the shell. Closely allied to the Nut-shells are the four native species of Leda, but they are readily distinguished by several differences in form and structure, One 58 Shell Life important advance in development consists in the production of the hinder part of the mantle into two long tubes or siphons, which are thrust out beyond the shell and reach up to the water above the mud and sand in which the creature burrows. The purpose of these OO siphons is to enable the Leda to remain safely buried whilst it gets a constant fresh current of water over its gills, and to bring microscopic food to its mouth. Through the lower of these tubes the fresh supplies pour in, whilst the vitiated current carrying off waste passes out through the upper tube. With a view to the better protection of these siphons the shell has been elon- gated backwards. In the Dwarf Leda (L. pygmea) the siphons are not very long, and they are united throughout their length, showing that though the mollusk affects deep water (20 to 86 fathoms) it does not burrow much below the surface of the mud, or indeed remain entirely covered by it. Its tubes may be entirely withdrawn into the shell, which closes all round as do the Nut-shells. The shell is scarcely a quarter of an inch long. The Beaked Leda (L. minuta) is a much larger species, and the great change in the shape of the shell shows that the creature is given to burrowing more deeply and to remain buried. The siphons, which are united only for half their length, have become much Hee baie longer in order to reach the water above, and the shell has become greatly lengthened behind for their partial protection, there being Dwarf Leda ~ order includes the Saddle- Nut-shells and Mussels 59 insufficient room in a shell shaped hke that of L. pygmea to withdraw the whole of the long siphons. The valves at this point do not fit closely. There is a slight gape, and this indicates that owing to the constant protrusion of the siphons the mantle is never able to extend the edges of the shell so that they will meet. In some other bivalves we shall see that the foot also is kept so constantly distended that the shell gapes at the front end also. The hinge-teeth are in this species less simple in their shapes, as will be seen in the figure of the interior of aleft valve. It is found in muddy gravel and sand between 20 and 100 fathoms deep, on our northern coasts. The two genera Nucula and Leda constitute the sole British representatives of the order Pro- tobranchiata, the bivalves in which the branchie or respiratory organs have the simplest character. They consist of parallel, unbranched, independent filaments arranged in two rows on each side of the central body-mass. In the next lowest group, the order Filibranchiata, the filaments have become so long that they are folded back upon them- selves and show signs of lateral adhesion. The oysters (Anomia), the Ark-shells (Arca), and the ———— Mussels (Mytilus). Saddle-oyster—under-side The Saddle-oyster (Anomia ephippiwin) is a thin, flat, little pearly shell found on old oyster-shells, crabs, 60 Shell Life rocks, and other submerged objects, and is not un- reasonably—though quite inaccurately—regarded by the ‘long-shore folk as the young of the true Oyster (Ostrea). It is not even closely related to the true Oyster, nor is it edible. It is by no means an easy task to persuade fishermen that these are not young oysters, but the quickest method of convincing them is to prise off the Saddle-oyster and exhibit its under- side as shown in our figure. It is then seen that there is a pear-shaped orifice in the lower valve through which an attachment plug passes and fixes the Saddle-oyster to its chosen support. No genuine Oyster is attached in this way, nor has it a hole in its shell. ‘The Common Saddle- oyster 1s about 2 inches across TEEW when full-grown, variable in Ta outline, but more or less cireular. Pe catia: It is never very thick, but varies showing mode of attach- In this respect according to age. ie Outside it is dull white in colour, or tinged with yellow, pink, or brown; within it is polished and opalescent. The lower valve in its growth follows the modelling of the surface to which it is attached, whether that be the smooth rounded stem of a huge seaweed, the rough sur- face of the rock, or the ribbed shell of a scallop. The upper valve, of course to a less degree, follows the shape of the lower. Normally the lower valve is flat and the upper one convex. There are no hinge-teeth as in the Nut-shells, though there is a half-moon shaped pad of cartilage to keep the valves apart when the single muscle is relaxed. The plug by which the shell is fixed to its support is ae uN ANI cL . VJ ~ \ Nut-shells and Mussels 61 attached to the upper valve and passes through the lower one. It appears to represent the byssus-threads of the Mussel and Scallop united into a solid mass. The expanded end evi- dently corrodes the living surfaces to which it attaches, for it is frequently found to be lodged in a little pit. The animal varies V7 in colour from yel- Right side of Anomia, with shell removed low. to red. and a, opening for hinge; m, adductor muscle; brown. Its mouth nes is large, and furnished with a pair of long slender lips. As the animal does not burrow, and is usually found solitary, it can develop its shell pretty equally in all directions; the mantle is therefore more or less circular like the shell, its margin fringed with two or three rows of yellowish filaments. Again, because it is not a burrowing or otherwise active animal, the white cylindrical foot is very small. There is a variety (aculeata) in which prickly scales are developed on the upper valve. i The only other British species is the ety atic Ribbed Saddle-oyster (A. patelliformis), of the smaller than the last, and attaining to little Saddie-eyster nore than half its dimensions. From 20 to 30 waved ribs radiate from the beak to the margin, and the shell is often ornamented with 62 Shell Life streaks or spots of red-brown, and by a number of fine overlapping scales. It is a common but little- known species, its range being only between the depths of 10 and 86 fathoms. Both these species appear to owe their security alike from storm and enemy to the thin flat form that sits so tightly on its chosen base, and affords little opening to the predatory fish or bird that might consider its thin body worth prising off. The Ark-shells (Arca) present an appearance very . different from the exceedingly thin Saddle-oysters. The Common Noah’s Ark (A. tetragona) is a quaint little yellow and brown box-like shell of distorted aspect that loves to spend its time in the crevices of rocks, or attached by its byssus to the empty shells of other bivalves.