HARVARD UNIVERSITY 1 Ls} LIBRARY OF THE Museum of Comparative Zoology HP. 200.) “maRARD UNIVERSITY: ¥ a4 1 ‘ brah | a \ ‘i x T Aa nu 1 ie wi eta ty, a wy \ va %, ) ey ¢ 4 ? f \ + m ? ? > a F tat Poly ‘J «7 ‘ H ’ & “ i \ j a ae (i i Ny y \ a } 5 at i RN SA Wine aa y ; WN bf f f i} “< h me ate uy " } in a Wit ib i \ LELAND STANFORD JUNIOR UNIVERSITY PUBLICATIONS UNIVERSITY SERIES ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA BY JAMES PERRIN SMITH PROFESSOR OF PALEONTOLOGY WITH FIFTEEN PLATES (ISSUED APRIL 14, 1914) STANFORD UNIVERSITY, CALIFORNIA PUBLISHED BY THE UNIVERSITY 1914 UNIVERSITY SERIES. TNHERITANCE OF Siukworms, I. Vernon L. Kellogg, Professor of wae mology. 89 pp., 4 plates. 1908. Price, $1.00. THE OPISTHOBRANCHIATE MOLLUSCA OF THE BRANNER-AGASSIZ Eixpene: TION TO BRAzIL. Frank Mace MacFarland, Professor of Histology. 105 pp., 19 plates. 1909. Price, $1.00. A Srupy or THE NormaL CoNSTITUENTS OF ‘THE PoTABLE WATER OF THE San Francisco PeninsuuA. 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SMITH PROFESSOR OF PALEONTOLOGY WITH FIFTEEN PLATES (ISSUED APRIL 14, 1914) STANFORD UNIVERSITY, CALIFORNIA PUBLISHED BY THE UNIVERSITY 1914 Fe a Witney ke ele ae ea ‘ i Rae a WOMOLAVET Vee oat tiga VERR GU A DOIOOS C08 ey CEM SHOIKEN AO CONTENTS. PAGE Peal recapitulation m progressive forms». 2 «2 2... 2 3-2 8 ase REPRE SOR ee eels Ren CO Tree le Y Soke allt pee Weed ti tog een eCele rai mO Metal cull cen Solute Mints re Sette ay) at Soe ee echio lO ene em LRCOM ANC ute CR ene wee se ata lel ac pehe de ye wal ac ii au ah oko Srtcrewiieiie OmlOMeny.., ba tian ae as wien be ee es See a Petes MOG evel OMMEMie Uratrma re! ial sulla wie. ek ck! oo! a epee ali Reversion SO eiis shat vd eaealiel< | ERA ak aa a era ume ee eal | SERTEGTC SST AIGSER Ge bn Ie A is SLE al Ae ag eee 0! Me MG Chie asthe wera, a ra ete Geir a hye ay Ra gS aN ok De PRR e sei nae) 2) ME Mel ieee) As, cl ieen = a, Wipe AN at DG iiet and descriptions of iwlustrations .9 9. 4.0 4. Ofek a OT ae Acceleration of Development in Fossil Cephalopoda JAMES PERRIN SMITH. IDEAL RECAPITULATION IN PROGRESSIVE FORMS. the one with simple persistence without modification, the other with complete modification. The former is almost realized in the Protozoa, the latter is approached by the higher vertebrates. All other organisms, in their development, fall somewhere between the two extremes, coming into being in simpler form, and becoming more complex in the course of life. Each starts out on somewhat the same plane of development as its distant ancestors, inheriting potentially all the characters of all its ancestors, tending to take on some characters that its ancestors never had, and to transmit the old and the new to its own posterity. Theoretically, each organism ought to recapitulate all its race his- tory, each stage of growth corresponding in character and in size to successive ancestral forms. This is true, in a general way, in some groups, for most later members of genetic series have increased in size with increased complexity of development. a THE development of organisms there are two theoretical extremes, FIG. 1. This is partly true even of the highly specialized Cephalopods, for there is a constant tendency to increase in size from the simple Goniatites of the Devonian to the complex Ammonites of the Jurassic. The increase in size accompanying the addition of ontogenic stages is especially strik- ing in a primitive genetic series of genera near each other in time, and relatively near the beginning of the race, as in the lineage of Goniatites— Gastrioceras—Columbites. 6 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA But even in these, while there is in general a constant increase in size of the successive mature forms, there is a much more rapid decrease in size of the corresponding growth stages. This fact is illustrated by the accompanying diagram, showing a constantly lengthening ontogeny FIG, 2. as more stages must be passed through before maturity is reached. The contrast between the size of mature Goniatites of the Paleozoic and that of the goniatite stages of later Mesozoic Ammonites is even greater; see for example the development of Goniatites of the Carbon- iferous (PI. I, figs. 1-9), and of Placenticeras, (Pl. XIII, figs. 22-28), a Cretaceous genus. The same thing is seen in the development of the genetic series leading up to Columbites of the Lower Triassic. Its imme- diate ancestor, Gastrioceras, of the Carboniferous, when mature might reach a diameter of several inches, as shown on PI. I, figs. 10-14; but the adolescent Columbites, (Pl. IV, figs. 1-10), ceased to resemble Gastrio- ceras at a diameter of about ten millimetres. And Tropites, a still later descendant of the same stock, in the Upper Triassic, ceased to show the gastrioceran characters at a diameter of three millimetres, (Pl. IV, figs. 11-21). Cretaceous Jurassic Triassic ONTOGENY, Permian Carboniferous Devonian JAMES PERRIN SMITH 7 In a genetic series of progressive forms all individuals in their development should start out, theoretically, from the same stage, since all must develop from an egg. Hach individual would have to pass through in its growth from the egg to maturity all the stages that the successive generations of mature forms passed through during the long history of the race. Characters that were present at maturity in the ancestors should appear by palingenesis in the development history of the descendants, and the ccenogenetic, or later characters, should grad- ually be pushed back into the ontogeny. In a general way, too, this is true. As, for instance, in the Ammonoid stock the primitive simple shell, with its calcareous proto- conch and siphuncle, when once introduced as a ccenogenetic or secondary character, persists throughout the history of the race, becoming a primary character, and finally appearing only as a palingenetic character in some of the modern cephalopods. All this is seen in the history of the race from the primitive Orthoceras of the early Paleozoic, with its chambered shell and siphuncle, but without the calcareous protoconch or embryonic shell. Some members of the Orthoceras group finally acquired a calcareous protoconch, and this soon introduced with it another cenogenetic character, the marginal position of the siphuncle, forming the group of Bactrites (Pl. XIV, fig. 7), which was to become the starting point for the Ammonoids and the Belemnoids. Some Bactrites began to become coiled, and developed into the primitive Goniatites, (Mimoceras, Pl. XIV, fig. 8). Others remained straight, but began to cover up the slender shell with the mantle, and finally to secrete a sec- ondary covering of lime to protect it, growing into the race of Belemnites. But even in the Belemnites the chambered shell, inherited from the parent Orthoceras is still retained as a youthful character, once ccenogenetic, but now so long present in the race history that it is pushed back into the larval stages, and finally appears as a mere reminiscence only in the em- bryology of some sepioids. The ccenogenetic lime secretion that covered the chambered shell of the Belemnites has had a similar history, disappearing in most modern forms, but retained as a vestigial character in the cuttlefish ‘‘bone.’’ All characters were once secondary or ccenogenetic, and all may be- come primary, and finally vestigial. 8 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA Lost STAGES. But recapitulation in later forms is by no means so simple as sug- gested by the diagram given above; the ontogeny is abbreviated, and the successive forms do not repeat their full history. There is a constant loss of stages or characters all along the race history, they being pushed back and crowded out of the ontogeny, as Hyatt expressed it. All Goniatities must have sprung from a Bactrites radicle, but only one, Agoniatites, shows a Bactrites stage. No later genera have even a reminiscence of it, so completely is it lost from the ontogeny. Probably all later Goniatites had for their ancestor the group of Anarcestes, and yet the Anarcestes stage persists only in Devonian and a few Carbonifer- ous genera, being lost, or buried, in the development of later groups. The first stage of growth in the shell of all Ammonoids is the pro- toconch; this is an adapted form, suitable to life in the egg, not corres- ponding to any ancestral form, yet remaining the same in all genera. It even keeps its minute size, about a half millimetre in diameter, whether the mature form is a pygmy of half an inch or a giant of six feet. The earliest stages of growth of several genera of Ammonites are shown on Pl. XIII. Much of the ancient history is gone through while the animal is in the egg, and thus obscured or even obliterated, even in living forms. In fossil forms it is wholly lost to us. And after the embryonic stage is passed, it is advantageous to the young animal to shorten, or at least, not to prolong, the larval development, during which it is helpless and at the FIG. 4. Cretaceous Jurassic eae Se a a Triassic ae Da | d F 2 | a a o G ie, Permian Cc S % O iN fees, WEs> Carboniferous Devonian 7 ee ee JAMES PERRIN SMITH 9 merey of enemies. Thus, even after the egg-stage, characters will be eliminated, or, at any rate, so obscured that they can not be recognized. So the diagram should show a constant shortening or eliminating of stages at the lower end of each ontogeny, corresponding to the egg development. It should also show a constantly increasing length of ontogeny, probably not in time, but in the number of stages gone through, and hence, by in- ference, an ever increasing rapidity of development. From this idea came Hyatt’s name ‘‘tachygenesis.’’ Thus, for example, the develop- ment becomes successively more complex in Bactrites, Anarcestes, Gonia- lites, Gastrioceras, Columbites, Tropites, all steps in the same series, even with the complete elimination of the earlier stages; while the actual length of the larval stage was probably not greater in Tropites than in Bactrites. Mesozoic genera, as a rule, show scarcely any reminiscences of ancestors older than the Carboniferous, except in the case of fixed or left- over types, such as Lecanites, which has persisted into the Middle Triassic with characters little in advance of its Devonian ancestor. Paleozoic and early Mesozoic genera repeat, in their ontogeny, their ancestral history with a fair degree of exactness, for they are not yet greatly affected by unequal acceleration of development, and scarcely at all by retardation or arrest of development. Their ontogeny is beauti- fully simple and direct, and in them it is easy to find genetic series of adult genera with which to compare the ontogenic series of stages in any species. Such simple development and positive recapitulation is shown in Gomniatites of the Carboniferous, (PI. I, figs. 1-9) ; Cordillerites, (Pl. XII, figs. 1-8), and Ussuria, (Pl. XI, figs. 1-14), of the Lower Triassic. Dis- tinet recapitulation with considerable acceleration is shown in the onto- geny of Columbites of the Lower Triassic, (Pl. IV, figs. 1-10) ; in the same genetic series, T'ropites, (Pl. IV, figs. 11-21), of the Upper Triassic, shows a recapitulation of nearly all the ancestral characters, but much obscured by unequal acceleration, or ‘‘telescoping’’ of characters and stages of development. In later Mesozoic genera the recapitulation of phylogeny in ontogeny is not so distinct, since all the disturbing factors have combined to obscure the record. All have still a goniatite stage at the beginning of their larval development, but in Cretaceous genera it is no longer pos- sible to point out with certainty the particular ancestral goniatite genus. The young of all that have been examined resemble the Carboniferous family Glyphioceratide, which may mean that all Cretaceous ammonoid genera came from that stock, or else, more probably, that the round form 10 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA was the safest for the larva. This would make the larval stages of these later forms almost wholly adaptive and ccenogenetic. This is illustrated by the development of Schloenbachia, (Pl. XIII, figs. 16-21), Placenti- ceras, (Pl. XIII, figs. 22-28), and Lytoceras, (Pl. XIII, figs. 10-15), all of the Upper Cretaceous, in which the larval stages are very much alike, although the phylogeny of the three genera is very different. Lytoceras goes back in an unbroken genetic series to the Lower Triassic, and prob- ably sprang from some Carboniferous member of the Prolecanitide. Placenticeras is a phylogerontic form of the Stephanoceratide, most likely an offshoot of the Tropitoidea of the Triassic, and hence of the Glyphioceratide. If this is true it has every right to resemble the Car- boniferous genus Goniatites. The case of Schloenbachia is not so clear, but it is probable that this genus is an offshoot from the Triassic Cerati- toidea, and hence from still a third Paleozoic phylum, the Gephyro- ceratide. Sharply contrasted with this uncertain and garbled recapitulation of their ancient history is their positive testimony as to their immediate ancestry. And what is true of these three genera chosen for illustration is true of all Cretaceous Ammonites. This is reflected in the lack of agreement in their classification by various authors, and the utter failure to construct a satisfactory family tree for them. Lytoceras and Phyllo- ceras are the only Cretaceous genera of which we know positively the genealogy ; in fact they are almost the only Jurassic genera of which this is true. UNEQUAL ACCELERATION. Useful characters tend to be inherited by the succeeding generations at constantly earlier stages, and finally may appear, in the ontogeny of later groups, simultaneously with characters that belonged to other genera in the genetic series. In other words, the growing young shell is not strictly in sequence Anarcestes, Goniatites, Gastrioceras, Columbites, Tropites, the family line, stretching from Devonian to Upper Triassic, but has in the successive stages some resemblance to each of them, with few characters lost, rather obscured by association with other characters that were not synchronous with them. The characters of later genera do, in- deed, appear successively in ontogeny, but some appear at earlier and still earlier periods of growth, until they may even get back into the larval stages. Thus the keel, which is a late character of the Tropitide, having been developed only towards the end of the Middle Triassic, is pushed JAMES PERRIN SMITH all back in the ontogeny of T'ropites, until it appears in the larval stage, as- sociated with septa like those of the Devonian Anarcestes, and form and sculpture like that of the Carboniferous Gastrioceras. The ontogeny of Tropites is shown on PI. IV, figs. 11-21, where it may be compared with the simpler development of Columbites. The ontogeny of the ancestral Goniatites is shown on PI. I, figs. 1-9. In a like manner, in the development of Clionites, (Pl. XV, figs. 1-12), the ventral furrow, which is a late or ecenogenetic character of the group T'rachyceras, is accelerated in inheritance until it appears in asso- ciation with characters belonging to genera far below Trachyceras in the series. The term, ‘‘telescoping,’’ which has been applied by Grabau to this phenomenon is graphic, but hardly accurate enough for use in strictly scientific nomenclature. FIxep TYPEs. The first step towards degeneration is cessation of progress, seen in the case of all persistent types. Such types may become finally ‘‘left overs,’’ fixed in the ancestral characters, anachronisms, or ‘‘contempor- ary ancestors.’’ They usually become dwarfed, or at least seem so, for they retain the small size of the ancient forms, of which they are the unmodified, or little modified descendants. Such types among Ammon- ites are Lecanites and Nannites, which persist until the Middle Triassic with the characters of Devonian and Carboniferous genera. (See Pl. III, figs. 1-3, Pl. ITI, figs. 4-8, for the characters of these genera). These dwarf genera are represented by few species at any time in their later history, showing by their very fewness the lack of that virility which is character- istic of progressive forms. Their ancestors, the Goniatites, and their con- temporary kinsfolk, the highly specialized Ammonites, are both charac- terized by abundance of individuals, species, and genera. Nannites and Lecanites are ‘‘poor-relations,’’ few, small, and unimportant, though won- derfully interesting, for they give us an insight into the beginning of the phenomenon of degeneration. STRETCHING THE ONTOGENY. The next step towards degeneration consists in prolonging the on- togeny, as when a specialized group remains longer in the larval and adolescent stages than did its ancestors, while finally reaching to the full perfection that they had attained. The best example of this is seen in aes ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA the development of Ceratites in the Germanic basin in the Middle Trias- sic.* Here we have a group descended from Meekoceras of the Lower Triassic, and in general as far removed from that genus in specialization as in time, but delaying in the Meekoceras stage, retaining until almost mature many of the characters of that genus, and scarcely progressing beyond it at maturity. Pavlow** has observed a similar phenomenon in the Ammonites of the Lower Cretaceous of Russia. In both cases we have a beginning of degeneration caused by unfavorable conditions of life in basins partly shut off from the sea. A beginning of this stretching of the ontogeny is seen in T'rachyceras of the Upper Triassic (Pl. XV, figs. 13-16), where stages that had long been obsolete in the group persist almost until ma- turity, probably brought out by atavism. ARREST OF DEVELOPMENT. The next step in degeneration is arrest of development, where the youthful stages are prolonged, and the form on reaching maturity finally fails to reach the complete development of that species, and does not attain to the complexity of its immediate ancestors. Such cases are known in the Brachiopods, where in a living species sexual maturity may be reached in stages much lower in specialization than the normal mature form, so much so that these stages have even been described as independ- ent genera. Such arrested forms may even give rise to a stock that never reaches the full generic evolution of its ancestors.* Dr. C. E. Beecher** has aptly described this same phenomenon: ‘‘In each line of progression in the Terebratellide the acceleration of the period of reproduction, by influence of environment, threw off genera which did not go through the complete series of metamorphoses, but are otherwise fully adult, and even may show reversional tendencies due to old age; so that nearly every stage passed through by the higher genera has a fixed representative in a lower genus. Moreover, the lower genera are not merely equivalent to, or in exact parallelism with, the early stages *See E. R. Philippi, Die Ceratiten des oberen deutschen Muschelkalkes. Pal, Abhandlungen von Dames und Kayser, Bd. VIII, Heft 4, 1901, p. 359. **Le Crétacé inférieur de la Russie et sa Faune. Nouv. Mém. de la Soc. Impér. Nat. Moscou. Tome XVI, 1901, Part I, p. 62. *Fischer and Oehlert, Brachiopodes, Mission Scientifique du Cap Horn, p. 50-60. ** Amer. Nat., vol. XXVII, 1893, p. 603. JAMES PERRIN SMITH 135 of the higher, but they express a permanent type of structure, so far as these genera are concerned, and after reaching maturity do not show a tendency to attain higher phases of development, but thicken the shell and cardinal process, absorb the deltidial plates and exhibit all the evi- dences of senility.’’ E. D. Cope,* too, has expressed himself clearly on this question: ‘“‘The acceleration in the assumption of a character, progressing more rapidly than the same in another character, must soon produce, in a type whose stages were once the exact parallel of a permanent lower form, the condition of inexact parallelism. As all the more comprehensive groups present this relation to each other, we are compelled to believe that accel- eration has been the principle of their successive evolution during the long ages of geologic time. Each type has, however, its day of suprem- acy and perfection of organism, and a retrogression in these respects has succeeded. This has, no doubt, followed a law the reverse of acceler- ation, which has been called retardation. By the increasing slowness of the growth of the individuals of a genus, and later assumption of the characters of the latter, they would be successively lost.’’ This state- ment of Cope might apply equally well to unequal acceleration or “‘tele- scoping’’ of characters, but in another part of the same work he gives a clearer statement:* ‘‘Where characters which appear latest in embry- onic history are lost, we have simple retardation, that is, the animal in successive generations fails to grow up to the highest point of comple- tion, falling further and further back, thus presenting an increasingly slower growth in the special direction in question.”’ Examples of arrest of development are very common among the Am- monites, especially towards the end of the history of stocks. These, naturally, are more common and better known in the Jurassic and Cre- taceous, where the family history is not so well understood, and where it is not possible to correlate the arrested stages with ancestral genera. Lecanites and Nannites, of the Triassic, are regarded by some au- thors as cases of reversion by arrest of development, but the writer re- gards them as fixed persistent types. Much better illustrations are found in the great families, Tropitide and Ceratitide, of which the genealogy is well known, and where the arrested stages may be compared with an- tecedent genera in the same line. Among the Tropitide the development *Origin of the Fittest, p. 142. *Op. cit., p. 13. 14 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA of Metasibirites, Homerites and Leconteva, illustrates clearly arrest of de- velopment, with accompanying retardation of characters, and partial re- version to ancestral types. Metasibirites is a dwarf, degenerate genus, confined to the Upper Triassic, in India, California, and the Alps. The ontogeny of only the American species has been published, but the statements made here are based on the development of several American species, of which only two have been described, Metasibirites (Tardeceras) parvus H. and S., and M. (Tropiceltites) Frechi H. and 8. (Pl. VII, figs. 1-10). In early youth Metasibirites Frechi is a typical Gastrioceras, with broad low trapezoidal whorls, strong umbilical knots, frequent constrictions, and simple gon- latitic septa. Towards maturity the whorls become higher, the sculpture begins to run up the sides, and ribs begin to develop from the knots, which themselves become weaker and often obsolete. These ribs run up to and finally across the venter. But before this is complete a weak keel appears, bounded in some cases by weak furrows. The keel speedily be- comes obsolete, often disappearing entirely at maturity. When nearly mature the shell in nearly all its characters is a minature of Acrochor- diceras of the Middle Triassic, but the septa remain goniatitic, or at least only very weakly serrated. This is not a persistence of Sibirites from the Lower Triassic, but an arrest of progress so that some of the characters fail to get beyond the complexity that they had in that genus. In other characters the genus has gone beyond Sibirites, in some respects even fallen short of it. The ~ genetic series of adult forms is as follows: Pericylus of the Subecarbonif- erous developed into Gastrioceras, which in turn changed over into Sib- writes of the Lower Triassic; this by gradually increasing strength of sculpture and increasing complexity of septa developed into Acrochor- diceras. There the stock became partly degenerate and development was arrested: The forms affected failed to grow up to the size and complex- ity of the immediate ancestor, Acrochordiceras, but stopped nearly in the Sibirites stage of development, and in some characters even reverted to the more remote ancestor, Pericyclus. The tendency to form a keel was strong in nearly all the groups of the Tropitoidea, and crops out weakly here in the temporary develop- ment of the vestigial keel. No member of Sibirites or Acrochordiceras ever possessed a keel, so its development in Metasibirites can hardly be charged to palingenesis of this character by heredity from some long dead Lower or Middle Triassic form. It is rather a manifestation of a latent JAMES PERRIN SMITH 15 tendency in all the Tropitoidea to form keels late in the history of the stock. All true Tropitoidea show this character well developed, and among the Haloritide Homerites shows the same tendency, and develops a vestigial keel just before maturity, losing it entirely at maturity, as shown on PI. VI, figs. 16-21. Leconteia H. and 8. has a somewhat similar history, with the same retardation of the septa, and the same reversion to the Pericylus ornamentation, but without the formation of a keel at any stage. This form is also illustrated on Pl. VI, figs. 11-15, for comparison with Metasibirites and Homerites. This parallel development in rather closely related genera may be called orthogenesis. The reappearance of the Pericyclus and Sibirites characters is undoubtedly atavism, but the parallel development of the keel in Metasibirites and Homerites can only be ascribed to the bringing out of a tendency always present, though previously latent. The immediate cause, in both cases, is the disturbance of heredity consequent upen arrest of development and incipient degen- eration. Another clear case of arrest of development is seen in Clionites, of the Upper Triassic. This genus, when fully developed, has the sculpture of Trachyceras, and a form something like it, but the septa are ceratitic ; and even when nearly mature Clionites is evolute and square shouldered, with prominent shoulder knots, like Tirolites, of the Lower Triassic. This genus, then, has a mixture of characters that ought not to occur together. In the ceratitic septa it shows a stoppage of development in the stage characteristic of Middle Triassic forms, and in the square-shouldered whorl and shoulder knots it has been arrested in a stage corresponding to a Lower Triassic genus. But in its sculpture and in the median furrow it is as far along as its immediate ancestor. This is shown on Pl. XV, figs. 1-8, in the development of Clionites (Traskites) robustus, where the youthful stages are very like Tirolites, differing from it in the possession of the median furrow, inherited from an ancestor later than Tvrolites. The mature stage of Clionites takes on the sculpture of Trachyceras and approaches it in form, but fails to reach the complexity of septation of that genus. Ordinarily Trachyceras does not show any trace of the Tiro- lites stage, but in the lower part of the Upper Triassic there are several species which have prolonged their ontogeny, and do show a distinct Tirolites stage. Such a species, Trachyceras duplex, is figured on Pl. XV, figs. 13-16. This species shows the beginning of retardation, which is more complete in Clionites. Still more complete arrest of development is seen in Cliontes (Californites) Merriami, Pl. XV, figs. 9-12, which has re- 16 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA mained in the Zirolites form, and septa, and developed little beyond it in sculpture, but has inherited the trachyceran furrow. It is then a lower form than the subgenus T'raskites, but lower in the sense of being more retrograde, that is more thoroughly retarded. Both are partial rever- sions towards Tirolites by loss of characters, but both have retained the furrow, which Tirolites never had, and which they have inherited from the progressive ancestor T'rachyceras. The genetic series is: TZvrolites, Lower Triassic; T’rachyceras, Middle and Upper Triassic; and Cliomites, Upper Triassic. It should be stated here that Trachyceras is a polyphy- letic genus, not all of its species coming from the line of Tirolites, but some from the stock of Meekoceras; and it is not yet known to which branch the type of the genus, T'rachyceras Aon, belongs. Another case of arrest of development is seen in Paraganides, of the Upper Triassic, Pl. VI, figs. 22-26, where a member of theNannites group has lagged behind its fellows until it is scarcely beyond Aganides of the Devonian and Lower Carboniferous, but shows its inheritance from more complex intermediate genera in the internal lcbes. This is the last mem- ber of a genetic series that began in Aganides, (Pl. I, fig. 15), continued in the fixed type Nannites (PI. III, figs. 4-8), and finally perished in the retarded and reversionary Paraganides. REVERSION. When a form develops normally and then strikes back to its ances- tral type we have real reversion. It is not known positively that we have any examples of this, but the development of Lituites, of the Silurian, Pl. XIV, fig. 6, and of Baculites, of the Cretaceous, Pl. XIII, figs. 1-9, is probably to be explained in this way. The ancestral stock was Orthoceras, Pl. XIV, fig. 1; then came Cyrtoceras, Pl. XIV, figs. 2 and 3; then Gyro- ceras, Pl. XIV, fig. 4; then coiled nautilian shells, Pl. XIV, fig. 5, and finally Litwites, after becoming coiled, strikes back at maturity to the straight orthoceran type. Most degenerate types are reversionary, at least in some characters, though none are probably completely so. Baculites among the ammonoids has a similar history. Its remote ancestor was Orthoceras; then came Bactrites of the middle Paleozoic; then the coiled Goniatites ; then the Ammonite stock of Lytoceras; and finally, after being coiled normally, it strikes back to the straight form of its progenitor. The reversion is only partial in either case. Such a partial reversion is seen also in Crioceras, of the Cretaceous, Pl. XIV, fig. 11, where the shell becomes uncoiled, and reverts partly to the JAMES PERRIN SMITH . By primitive type that came between Bactrites and the coiled Goniatites, a type that is unknown as a fossil, but one whose former existence is indicated by the young stage of Mimoceras, Pl. XIV, fig. 8, itself one of the earliest and most primitive of Goniatites. Partial reversion is probably a common phenomenon among the Ammonites, but outside of such striking cases as those mentioned above it can be recognized only in the reappearance of the same character or characters in later forms. This is possible only when the genetic series is well known, which is but seldom the case. Beyrichites, in the Middle Triassic, Pl. VIII, figs. 14-23, after becom- ing rough shelled and ornamented, reverts to the flattened shape and nearly smooth shell of its ancestor, Meekoceras, so much so that it has several times been described as Meekoceras. Some species of Trachyceras in the Upper Triassic, after gcing through the rough shelled stage char- acteristic of that genus, become flattened and nearly smooth, and thus show a partial reversion to the far removed parent Meckoceras, although they are still progressive in the complex septation. Reversion by arrest of development is far more common than the sort just described, but in this case, too, the reversion is only partial. Metasibirites has already been mentioned as an example of this, where there is a reappearance of the sculpture of Acrochordiceras, and of the form and septa of Pericyclus or Gastrioceras, an apparent palingenesis of the long extinct genus Sibirites, but with some later characters that Sibirites never had. The so-called ‘‘Ceratites’’ of the Cretaceous give us the classic example of reversion by arrest of development. Although there were no Goniatites after the Paleozoic, nor Ceratites after the Triassic, there are in the Upper Cretaceous several genera with form and septa so lke those Paleozoic and Triassic groups that they were once called ‘‘Cera- tites.’? We now know that they are not cases of generic persistence through this long time, but are retarded and arrested forms, reverting to goniatitic or ceratitie stages of growth after long obsclescence of those characters, but with such a commingling of characters from various steps in the family history that it is impossible to determine what was the particular ancestor. One of these, Neolobites (Pl. X, fig. 1), although a Cretaceous genus, is arrested in the Goniatite stage. No adult Gonia- ' tites are known in the immense interval between the Permian and the Cretaceous. But also no genus is known in the Paleozoic that is com- 18 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA parable to Neolobites, and probably none like it ever existed. Its characters are a combination handed down from various members of its long family line. Other genera of the Cretaceous have ceratitic septa, and here again we have a reversion by arrest of development to an older type of structure. It is not likely that these ‘‘Pseudoceratites’’ are really reversions to the genus Ceratites, for they appear to belong to several different phyla, in which the stage of development with serrated lobes was present in either Permian or Lower Triassic time. The resemblance is so marked that Steinmann* regards Heterotissotia (Pl. X, figs. 2-4) of the Cretaceous as a direct descendant of Ceratites of the Middle Triassic, and does not even regard it as a case of atavism, or arrest of development, but simply a persistence of the genus, intermittent because of our lack of knowledge of the intervening forms. No doubt there are numerous gaps in our existing records of extinct faunas, and it is premature for us to be too positive in our denial of the possibility of this being the correct explanation. But that it is extremely improbable nearly all paleontologists will agree. Steinmann compares Heterotissotia with Ceratites semipartitus, which according to Philippi* is a somewhat degenerate type, already reversionary, and probably not an ancestor of later forms. It is, then, more probable, if in the ‘‘Pseudoceratites’’ we have a case of atavism, the reversion is to some still older member of the Ceratitoidea, the Meekoceras group, for instance Aspidites or Koninckites, of the Lower Triassic. In any case, whether it is due to atavism, or to independent develop- ment of the same characters in different stocks and in widely separated times, this is a remarkable case of parallelism. Another of the ‘‘Pseudo- ceratites,’’ Sphenodiscus, of the Upper Cretaceous (Pl. X, fig. 11), approaches closely to the septation of the primitive Arcestoidea of the Permian, especially Waagenoceras (Pl. X, fig. 12) and Cyclolobus. Also here there is no probability of atavism, for the phylum of the Arcestidae seems to have died out at the end of the Triassic, and the affinities of Sphenodiscus seem to point to a relationship with the Jurassic Stephano- ceratidae, which certainly did not come from the Arcestidae. *Sitzungsber. Niederrhein. Gesell. fiir Natur- und Heilkunde zu Bonn. Naturwiss. Abtheil. 1909. Probleme der Ammoniten-Phylogenie (Gattung Hete- rotissotia), pp. 1-16. *Die Ceratiten des oberen deutschen Muschelkalkes, Pal. Abhandl. Bd. VIII, 1901, Heft 4, p. 357. JAMES PERRIN SMITH 19 But in all speculations on the phylogeny of Cretaceous genera we must not forget that there still exists a great gap in our knowledge of the connections between Triassic and later groups, and that some of the stocks may possibly have lived on in unknown regions, to reappear in later ages so greatly modified that their ancestral history comes out only in their reversion to the parent type, when senescence has awakened the latent tendencies of their far distant youth. A case that may illus- trate this is the parallelism of Paratissotia of the Cretaceous, Pl. X, figs. 8-10, with Otoceras of the Lower Triassic, Pl. X, figs. 6 and 7. Otoceras belongs to the family Hungaritidae, the most ancient line of the Cera- titoidea, and Paratissotia belongs to the Amaltheidae, which are thought hy some to have come from the Ceratitidae. In this case the parallelism may be due to atavism. In the cases discussed above, generic persistence from the Permian until the Upper Cretaceous is out of the question, and even the families referred to have not outlived the Triassic in most cases. But the Cretaceous forms must have had Paleozoic and early Mesozoic ancestors which were in the transition between the goniatitic, ceratitic and ammonitie stages of development. And being all somewhat retarded, and in most cases affected by arrest of development, it is highly probable that they would revert to some of the characters of those remote pro- genitors. GENETIC SERIES. Ever since the acceptance of the theory of evolution, genetic series have been sought by geologists with more or less suecess. Waagen’s studies in the Formenreihe of Oppelia, and Hyatt’s ‘‘Genesis of the Arietidae’’ have become classic. But some more conservative paleon- tologists have always cherished secret doubts of the demonstration, while admitting the truth of the principle. It is extremely doubtful if we can establish any genetic lines of species, or that we can ever tell from which particular species a certain genus originated. Did it, indeed, come from only one? What the paleontologist sees is rather a group of species tending in somewhat the same direction; and those species most alike he classes, for convenience, under one genus. Further, the conservative paleontologist can not always point to the individual genus from which another genus sprang; and if he does he is probably mistaken. Every virile progressive stock is characterized by its wealth in variation, its genera and species as we grade them, any one of which, or all of which, might have been ancestors of later forms. 20 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA There are three sorts, or rather ideas, of genetic series, as shown by the accompanying diagrams. No. I, on the diagram, where we have a narrow straight lne of connected genera or species, would show straight natural selection, if this were in harmony with the evidence of paleontology, but it is not. FIG. 5. No. II in the diagram gives the commonly accepted idea of a genetic series. Hyatt’s genesis of the Jurassic Ammonites proposes such a genetic line, and derives all the later forms from Psvloceras, which is itself a degenerate. I have always agreed with Steinmann in thinking that this idea was improbable, to say the least. We find early in the Lower Jurassic the Arietidae distributed in Europe, Asia, North and South America, and the Indian Ocean; hence it is unlikely, leaving morphology out of the question, that the rare dwarf Psiloceras of the Mediterranean Region was the parent of this varied progeny. The theory expressed in No. II in the diagram has always reminded the writer very forcibly of the Noachian fable in the history of the human race. No. III in the diagram shows the conditions as the paleontologist finds them, regardless of any theory. He sees a number of species in a genus, and a number of genera, in a family, all tending in somewhat the same direction, as he traces them upwards through the geologic ages. He finds no complete unbroken series, but a series of steps. Is this orthcgenesis? In a general way it is, although giving a name to a phenomenon is not giving an explanation. There are only certain lines of variation possible, and when the organism starts out with certain characters it can vary only in more or less definite direc- tions, some of which will coincide in different species, genera, and families. There need not be any mysterious force directing the evolution ; it may be merely the limitations of the characters of the organisms. JAMES PERRIN SMITH Pel The best genetic series of Ammonoids are found in the Paleozoic and early Mesozoic. There we get a nearly unbroken series of adult forms that show by their sequence and intergradation that they are genetically connected. In most of these genera we have also their individual development repeating the ancestral history, not the whole history distinctly, but that part nearest to them most positively. Such a series leads from the Glyphicceratidae through Gastrioceras of the Carboniferous, to Columbites of the Lower Triassic, and up to the Tropitidae of the Upper Triassic. The writer is strongly of the opinion that this phylum will yet be traced still higher, into the Arietidae and Stephanoceratidae of the Jurassic. Such a series is seen also in the Ceratitoidea. The parent, or radicle, of this group, Lecanites, as we know it in the Triassic, is still virtually a Goniatite, with simple unbranched septa, and repeats the race history of the Devonian Gephyroceratidae. The more primitive members of the Meekoceratidae of the Permian and Lower Triassic repeat this part of the history, and all show a distinct Lecanites stage. The earlier members of the Ceratites are still nearly smooth, and intergrade with the later members of the Meekoceratidae, still showing in their youth a decided reminiscence of Lecanites. From the earlier and simpler smooth Ceratites there branched out two groups of rough shelled forms, one leading towards the keeled Ceratites, group of C. trinodosus, the other leading through the group of C. bosnensis to the Trachyceratea, all connected by series of mature forms, but not showing their phylogeny in their ontogeny, except in cases of arrest of development and retardation. The division between Permian and Triassic was a deadline for most Paleozoic groups; on the one side we have rugose corals and tabulates, on the other the modern Hexaccralla; on the one side Productus and Orihis, on the other a predominance of Terebratulacea and Rhynchonel- lacea; on the one side Palwccrinoidea, cn the other Neocrinoidea. It is not so with the Ammonoids, for in them there is a nearly perfect transition, not with any species, but with a number of genera surviving from Permian into the Lower Triassic, and with many getting across the line so little modified that, while we call them by different generic titles, they are still virtually the same as their Paleozoic forebears. The following genera survive from Permian into the Triassic: Otoceras, Hungarites, Xenodiscus, Xenaspis, Pronorites, Medlicottia 22 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA (Episageceras), Lecanites (Paralecanites), Dalmatites, Popanoceras, Celtites (Paraceltites). The following Permian genera had reached a stage of development as high as that of Triassic forms, but are not yet known in Triassic faunas: Cyclolobus, Waagenoceras, Thalassoceras, Stacheoceras. The following genera appear at the very bottom of the Triassic, already fully developed, and must have existed somewhere during Permian time, although they are not yet known in any Permian faunas: Ussuria, Columbites, Monophyllites, Nannites, Meekoceras, Flemingites, Heden- stroemia, Pseudosageceras, Ophiceras, Aspenites, Lanceolites, Cordiller- ites. Kymatites and Ambites of Waagen may not be goniatitic survivors from the Permian faunas, but merely Meekoceratidae in which the lobes have not been well preserved on account of weathering. The later groups, such as Proavites, Metasibirites, Paragandes, Tornquistites, Dieneria, Leconteia, Tropiceltites, Styrites, Polycyclus and Lobites, all of which are as simple as Permian forms, are merely cases of arrested de- velopment and reversion. Karpinsky’s* work in tracing the Ammonoids of the Carboniferous into the Permian, and comparison of ontogeny with phylogeny, has given us our most convincing example of real genetic series. The work of J. P. Smith** has carried our knowledge of the Ammonites further back into the Carboniferous, and later he has traced many of the Carbonifer- ous genera and families into the Triassic,* combining the study of onto- geny and phylogeny. The monographs of Diener, von Krafft, and Waagen, on the Lower Triassic Cephalopoda of India, of Kittl and von Arthaber on those of the Mediterranean Region, have added greatly to our knowledge of the transitional faunas at the border-line between Paleozoic and Mesozoie, and out of them have eome some real genetic series. The combined re- sult of all this work is given here in the form of a table showing the re- lationship of the early Mesozoic Ammonoids to those of the Paleozoic. *Ueber die Ammoneen der Artinsk-Stufe, Mém. Acad. Impér. Sci. St. Péters- bourg, 7th Ser. Vol. XX XVII, No. 2, 1889. **The Carboniferous Ammonoids of America, Mon. XLII, U. S. Geological Survey, 1903. *The Triassic Cephalopod Genera of America, Prof. Papers No. XL, U. 8S. Geol. Survey, 1905. JAMES PERRIN SMITH 2a Tropitoidea Ptychitoidea Lytoceratoidea Pinacoceratoidea c amen | Arcestoidea o Geuas o 2, 3 o 2 Soar 3 ral So) 4 o On oS SS 2 — = 72 o °o s = = ° Ora = 2 ° = a % = @ oe £ € 3 hie ose Ss = ek = c c oO Ss oO ore o — FT aa Re i t ay & { aay a < ul A oY AI i ' } fo / S ef oN S i ! SiS Dea « a £ SY r } Pronjoritjidae} } ES 8 , a 3 oer i i I a a P| < ot an | ! oat = / = °o e ~~ 7 u 3 rr Ent o | ' v hee eA (?) O i Oo + —— ooo —-+. eS " z 1 Ua a 1 7 i 1 =< D4 E 1 ls es, = 1 = = . { = 7 7 oa S s 38 | ert ! v4 ; i = S = of i / > Bie oy i ; / 4 ees mets ast , ! cat 6 x rO) Q Saw 1G; | j ! / 3 ! , Pi 2 Go A i ! = | ° 4 2 1 1 3 3 ‘ td ~ ra H i gat | i 7 = c ® a4 = ¥ z S| 2 fz : rs is < 2 EN Be ase / a Oia: - ts i Cy / a 2 fo J af @# eB ie off. a) f 3 4 BH a Ky/ ' @ a x s} 2, et A = ‘ D ot Sof % Oo meer) 5 ae rs) > == c = bad a _— = <= ne mI Poe ae = NS 2 Pad Pe fas zZ ~> wo eA as fe) fm eet > A a = I a { testi = has { = 3 “NY A 1 It is not complete, and is, of course, subject to constant revision, but it does show probable genetic series, in the light of our present knowledge of the subject. In his studies of the genealogy of Jurassic and Cretaceous genera Steinmann* has gone to great lengths in finding genetic connections with Triassic genera, where connecting links are absolutely unknown, and ex- tremely improbable. In scme instances he does make a strong case for relationship, but none for generic persistence. The doubtful relation- *Rassenpersistenz bei Ammoniten. Eine Erwiderung. Centralblatt ftir Geol. Min. und Pal. 1909, No. 8, pp. 199-208, and 225-232; and in Probleme der Ammoniten-Phylogenie (Gattung Heterotissotia), Niederrhein. Gesell. fiir Natur. etc. 1909, pp. 1-16; also in Die Abstammung der “Gattung Oppelia” Waagen. Centralblatt fiir Geol. etc. 1909, No. 21, pp. 641-646. 24 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA ships he brings out may be explained much better on the basis of rever- sion by arrest of development, as has already been shown under the head of reversion. CONVERGENCE. It is impossible to conceive of the same species or genus as originat- ing in different times, or in different places. But natural selection sorts out certain characters, or environment calls them out, and so we often get very similar results from diverse materials. Similarity of habit pro- duces external, but not fundamental, similarity of characters. In the case of forms living together in time and place, convergence may well be due to mimicry, and thus explained by natural selection. But where the forms are separated by geologic ages, mimicry can not be appealed to: In the case of reversion by arrest of development we have a virtual reappearance of generic types in widely separated epochs. Only, when we know their history, we do not call the aggregation of characters by the same generic names, especially since the reversionary forms are usu- ally easily to be distinguished from the older types. Thus Arpadites, Pl. VIII, figs. 1-10, and Beyrichites, Pl. VIII, figs. 14-23, both show a partial reversion towards their ancestor Meekoceras, yet neither genus need be confused with the ancient progenitor. Convergence is sometimes seen in widely separated stocks and in widely separated times. Hutomoceras of the Middle Triassic, Pl. IX, figs. 5-7, the end genus of the Dalmatites-Hungarites stock, has been confused with the Upper Triassic Discotropites (Pl. V, figs. 1-138), a late member of the genetic series leading up from Gastrioceras-Columbites to the Tropitide. Ontogeny shows the heredity of the two genera to be differ- ent back to the Devonian. Their resemblance can hardly be due to at- avism, for their development is not parallel, as both genetic series of adults and ontogeny of each generic step shew. It can also hardly be due to natural selection, for along with these keeled members of each stock there are numerous others without keel, as the geologic record shows, _ equally prosperous and prolific. It is also net due to the inheritance of this character from a common ancestor, for the remote ancestors were not common, and did not possess the keel, anyway. Again, we may have parallel development of very similar characters in nearly related stocks. As an example of this may be cited the develop- ment of the ventral keel in the Dalmatites-Hungarites-Eutomoceras phy- lum, and the same thing in the Meekoceras-Ceratites line. Hutomoceras JAMES PERRIN SMITH 25 has a keeled lineage extending back to the Devonian, while the keeled Ceratites extend no further back than Middle Triassic. But the tendency to form a keel sometimes crops out even in the ancestry of Ceratites, since at least one species of Lecanites has shown this character. And both stocks appear to have come from the same Devonian genus, Gephyroceras, Ceratites from the main group, and Eutomoceras from the keeled sub- genus Timanites, as shown in this series: Gephyroceras-Lecanites-M eekoceras-Ceratites ; Timanites-Dalmatites-Hungarites-Eutomoceras ; Timanites-Aspenites-H edenstroemia-Pinacoceratidae. It would seem that there may have been in the descendants of the Gephyroceratide a strong tendency to form keels. This was already present in Timanites, a subgenus and contemporary of Gephyroceras, and is continuous in the Hungaritide and Hedenstreminez, which branched out from Timanites, as shown in Longobardites, Pl. 1X, figs. 14-16. The same character appears belated in the keeled Ceratites, certainly not in- herited from the collateral Timanites branch, and not known to have been present in the ancestor of the two stocks. Equally difficult to explain is the apparent genesis of the polyphy- letie genus Trachyceras from the two lines, one from Meekoceras-Cera- tites, the other from Tirolites. To state that both lines had a strong tendency to develop rough shells, a median furrow, and complex septa does not explain the phenomenon. Nor yet does it explain the strong re- semblance of mature Sagenites of the Tropitide to Trachyceras, so strong, in fact, that careful paleontologists have confused them, although their ontogeny separates them at once. The term orthogenesis is a statement of a fact, rather than an explanation. Ammonites have developed constantly in certain directions, in form and ornamentation of the shell, and increasing complexity of septation, in parallel series coming from the same or nearly related ancestors, as well as in series coming from different ancestors. In neither ease are the characters hereditary, though in both cases the tendency to develop those characters seems to have been hereditary. Genera derived from nearly related ancestors have frequently become more alike with the lapse of time, and this has also occurred often with genera whose ancestry was wholly different. This has made the study of Ammonite-phylogeny exceedingly difficult; in it fact and fancy have been so mixed that it has sometimes been called the ‘‘happy hunting eround”’ of theorists. But it has also been the happy hunting ground 26 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA of observers of fact. Along with speculations concerning the phylogeny of the Ammonites there has been a much greater mass of painstaking accurate systematic work, by which species have been carefully recorded, variation and morphology studied most minutely, and a wealth of mate- rial amassed for the use of the philosophic student of evolution. CONCLUSION. It may be that, when this paper is read by ardent members of the ‘‘Hyatt school’’ of paleontologists and adherents of the biogenetic law, they will be inclined to call the writer a deserter from the camp, and to suggest that the paper ought to have been entitled, ‘‘ Why recapitulation does not recapitulate.’’ The writer is still a firm believer in the bio- genetic law, but that law is not such a simple thing as it was once thought to be. In the youth of every theory everything is beautifully clear, and ideally simple. As time goes on we are compelled to drop one idea after another, until it almost seems that the whole will be lost. When sceptics concerning the recapitulation theory throw up to us that ontogeny does not always recapitulate phylogeny, we are prepared to admit this, even to go further and admit that it does not often recapitulate. In fact, the writer would be prepared to go still further, and to state that, in the sense in which the term has been used by most adherents of the theory, it never recapitulates. Our over-zealous friends have claimed too much, and have done more to prevent general acceptance of the theory than a host of enemies. JAMES PERRIN SMITH a ILLUSTRATIONS. Diagram, showing ideal recapitulation, with corresponding stages of growth of the same size. Text-figure No. 1. Diagram, showing corresponding stages of growth in later forms reduced in size. Text-figure No. 2. Diagram, showing theoretical recapitulation of phylogeny in ontogeny. Text-figure No. 3. Diagram, showing actual recapitulation of phylogeny in ontogeny, with lost stages. Text-figure No. 4. Diagram, showing genetic series, I showing theoretical straight natural selection; II showing periodic branching out from radicles; III showing orthogenetic series as seen in the paleontologie record. Text-figure No. 5. Diagram showing the family tree of the Paleozoic and early Mesozoic Ammonoid genera, showing the complex branching, and parallel development of groups that are usually classed together. Text- figure No. 6. Orthoceras, Pl. XIV, fig. 1, a representative of the ancestral radicle of the Cephalopoda. Cyrtoceras, Pl. XIV, figs. 2 and 3, a transitional group, intermediate between Orthoceras and Nautilus. Gyroceras, Pl. XIV, fig. 4, a further development towards Nautilus. Nautilus (Discites), Pl. XTV, fig. 5, a close-coiled Paleozoic member of the nautiloid group. Bactrites, Pl. XIV, fig. 7, the primitive ancestral stock of the Ammo- noidea, transitional from the orthoceran group. Mimoceras, Pl. XIV, fig. 8, a primitive Goniatite, the probable ancestral type of most of the Goniatitidae, transitional from Bactrites. Gephyroceras, P1. III, figs. 9-11, the goniatite ancestor of the Ceratitoidea. Aganides, Pl. I, figs. 15 and 16, a primitive member of the Glyphio- ceratidae, possibly transitional from Gephyroceratidae. 28 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA Iituites, Pl. XIV, fig. 6, a reversionary Nautiloid, striking back towards Orthoceras. Timanites, Pl. III, figs. 12-14, the Paleozoic goniatite ancestral stock of the Hungaritidae, transitional from Gephyroceras. Goniatites, Pl. I, figs. 1-9, a group transitional from the Goniatites to the Ammonites; the distant ancestral stock of Tropitidae and Arcestidae. Gastrioceras, Pl. I, figs. 10-14, a progressive development from the Goniatites; the family radicle of Tropitidae and Arcestidae; a form with the septation of a Goniatite, but with the sculpture and inner structure already advanced to the stage of Ammonites. Paralegoceras, P\. I, figs. 1-5, a more advanced member of the gastrio- ceran stock, showing the advance towards becoming an Ammonite. Schistoceras, Pl. II, figs. 6-13, a direct transition from the Glyphio- ceratidae towards the Tropitidae. Waagenoceras, Pl. X, fig. 12, a late Paleozoic member of the Arcestidae, showing an advance to Mesozoic characters. Ussuria, Pl. XI, figs. 1-14, transitional Ammonite, showing distinct re- capitulation of race history in ontogeny. Cordillerites, Pl. XII, figs. 1-8, transitional from Goniatite to Ammoniie, showing simple and direct recapitulation in entogeny. Pronorites, Pl. XII, figs. 9-12, ancestral stock of Cordillerites. Aspenites, Pl. IX, figs. 1-4, transitional from Gephyroceratidae to Pinaco- ceratidae, showing strong reminiscences of the Devonian radiecle, Timanites. Meekoceras, Pl. VII, figs. 1-12, the primitive stock of Ceratitidae, con- necting this group with Lecamtes, the family radicle. Inyoites, Pl. LX, figs. 8-13, an accelerated member of the Hungaritidae, showing convergence with the stock of Tropitidae. Paranannites, Pl. XT, figs. 15-20, a primitive progressive link between Nannites and the Ptychitidae. Columbites, Pl. IV, figs. 1-10, a primitive Ammonite, transitional from Gastrioceras to Tropitide, showing simple recapitulation; this is the probable radicle of Tropites and its near kindred, and connects them with the Glyphioceratide. JAMES PERRIN SMITH 29 Lecanites, P|. III, figs. 1-3, an unprogressive or persistent form, an Am- monite retarded in the Goniatite stage of development, probably representing the radicle of the Ceratitoidea, and connecting them with the Gephyroceratide. Nannites, Pl. III, figs. 4-8, a persistent, unprogressive type, a Mesozoic Ammonite retarded in the Paleozoic Geniatite stage of development ; probably representing the radicle of the Ptychitidae. Tropites, Pl. 1V, figs. 11-21, a progressive Ammonite, showing distinct re- capitulation, but with very unequal acceleration, or “‘telescoping”’ of characters and stages of development. Lytoceras, Pl. XIV, fig. 10, a persistent group of Ammonites, lasting with little change throughout the Mesozoic. Longobardites, Pl. IX, figs. 14-16, family Pin- acoceratidae. Eutomoceras, Pl. 1X, figs. 5-7, family Hungar- itidae. Illustrating converg- Discotropites, Pl. V, figs. 1-13, family Trop- yap cs different stocks, ieee in the development of i é the keel and Ipture. Paratropites, Pl. V, figs. 14-19, family Trop- a Signe ida A good example of or- itidae. thogenetic evolution. Ceratites, Pl. V, figs. 20-26, family Ceratitidae. Gymnotropites, Pl. VIII, figs. 11-13, family Tropitidae. Paraganides, P1. VI, figs. 22-26, family Ptychitidae, retarded and rever- sionary to the primitive Glyphioceran stock. Lecontera, Pl. VI, figs. 11-15, family Trop- ite Reversionary, by ar- itidae. rest of development; Metasibirites, Pl. VI, figs. 1-10, family Trop- /showing vestigial char- itidae. acters, and probable or- Homerites, Pl. VI, figs. 16-21, family Trop- thogenesis in closely al- nee hed stocks. Arpadites, Pl. VIII, figs. 1-10. Showing reversion to the ancestral J/eekoce- Beyrichites, Pl. VIL, figs. 14-23. aia pure 30 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA Showing similarity of Schloenbachia, Pl. XIII, figs. 16-21. young stages, due to - adaptation in stocks Lytoceras, Pl. XIII, figs. 10-15. es : re whely cae Placenticeras, Pl. XIII, figs. 22-28. The young stages are probably ecenogenetic. Baculites, Pl. XIII, figs. 1-9, a reversionary form from Lytoceras. Trachyceras, Pl. XV, figs. 13-16, one of the most highly specialized of the Ceratitidae; showing the beginning of arrest of development in the prolongation of the entegeny, and persistence of the ancestral Tiro- lites stage throughout adolescence. Clionites, Pl. XV, figs. 1-8, a retarded descendant of Trachyceras, rever- sionary by arrest of development toward Tvrolites. Clionites (Califormtes), Pl. XV, figs. 9-12, a form still more strongly reversionary than the preceding species, with almost complete palin- genesis of Tirolites characters, but with inheritance of the trachy- ceran furrow and sculpture from its immediate ancestor; these are characters that Tirolites never had. Otoceras, Pl. X, figs. 6 and 7, a transitional Permian genus. Paratissotia, Pl. X, figs. 8-10, a Cretaceous genus, arrested in develop- ment, and showing atavistic reversion to characters very like these of Otoceras. Waagenoceras, Pl. X, fig. 12, a Permian genus, primitive and progressive. ’ Sphenodiscus, Pl. X, fig. 11, a Cretaceous genus, arrested in development, and showing a close approach to the septation of Waagenoceras. These two genera do not belong to the same line of descent, hence the convergence is not due to atavism. Heterotissotia, Pl. X, figs. 2-4, a Cretaceous genus, showing arrest of de- velopment, and reversion to some form like Ceratites, but probably not to any member of the Ceratitidae. Ceratites, Pl. X, fig. 15, a Triassie genus, like the reversionary forms of later Cretaceous groups, the ‘‘ Pseudoceratites.” Neolobites, Pl. X, fig. 1, a Cretaceous genus, showing arrest of develop- ment and reversion to the Goniatite stage, though probably not to any known Paleozoie genus. EXPLANATION OF PLATES. Puats I. Goniatites crenstria Phillips, Lower Carboniferous, Arkansas. Fig. 1, a-j, development, shown in septa, from protoconch to ma- turity. Fig. 2, early larval stage, diam. 0.47 mm. Figs. 3 and 4, larval stage, diam. 0.92 mm. Figs. 5 and 6, adolescent stage, diam. 1.29 mm. Figs. 7-9, adult shell and septa. A highly specialized Goniatite, and a representative of the group radicle of the Tropitidae and Arcestidae among the Mesozoic Ammonites. Gastrioceras Listeri Martin, Coal Measures, Arkansas. Figs. 10-11, adult shell. A still more highly specialized Goniatite, showing further progress toward the Tropitidae. Gastrioceras Branneri Smith, Coal Measures, Arkansas. Figs. 12-14, adult shell and septa. Agamdes rotatorius de Koninck, Lower Carboniferous, Indiana. Figs. 15 and 16, adult shell. The genera illustrated on this plate show the stage of evolution of the common Carboniferous groups, and the early ancestral types of the Arcestidae and the Tropitidae. All figures on this plate are from J. P. Smith, Carboniferous Am- monoids of America, Mon. XLII, U. S. Geological Survey, 1903. PLATE | Puate IT. Paralegoceras iowense Meek and Worthen, Coal Measures, Iowa. Fig. 1, adult specimen. The two species of Paralegoceras figured on this plate show a transi- tion from Gastrioceras to Schistoceras. Paralegoceras Newsomi Smith, Coal Measures, Arkansas. Figs. 2-4, adult shell and septa. Fig. 5, adolescent stage. Schistoceras Hildrethi Morton, Coal Measures, Ohio. Figs. 6 and 7. The three species of Schistoceras figured on this plate show a distinct step toward the Arcestidae, although it is not probable that any one of © them was the family radicle. Schistoceras fultonense Miller and Gurley, Coal Measures, Illinois. Figs. 8-10. Schistoceras Hyatti Smith, Coal Measures, Texas. Figs. 11 and 12, adult shell and septa. Fig. 13, adolescent stage. The genera illustrated on this plate show an advance of the Glyph- ioceratidae towards the Arcestidae and the Tropitidae. All figures on this plate are from J. P. Smith, Carboniferous Am- monoids of America, Mon. XLII, U. 8. Geological Survey, 1903. Pani Ie if ey, Hil mine Mh, Wn Hy ( in tiaie * mi 2 at ; Jib i ) ‘ea ; * aaa snes mais Me 0 cape pian ; (apie! eri l, wi syis A ya nee re PUP ANAL ater eh ci u , AS r, 4 ha i - iM ; ? } ‘ ioe « A ie i Webi chaea . a mn ut vi! ys ‘ ne oa ‘ t« ¢ eae at ‘es mM H JAR ie i iY ) i | j ' -& vi . ) The 4 r f a * » , Ler. iw et ys ' 4 ar oe | i 2 , f r { AD : \ a) ; : { | ee a lis Ce aad“ j ' nr Pid : YW . i o ier! es , y ) Yi (ae oA (i f WO) ; mids oF 3 * uy :* ii j | id ] * ) ; Lod ‘ ha ¢ - Sty o .* : : ih. 7 I } : iy aly Li a] vf | 7 ns y se ‘ ¥ +, u Ey. ry ie rv) BY - ry, ey) i reba > vai 4 7 4 . <> as i = ' 5 = Puate III. Lecanites Vogdesi Hyatt and Smith, Middle Triassic, Nevada. Figs. 1-3, adult stage, showing persistence in the Goniatite stage, a beginning of arrest of development. This species retains many of the characters of Gephyroceras of the Devonian. Nannites Dienert Hyatt and Smith, Lower Triassic, California. Figs. 4-8, adult stage, showing persistence in the Goniatite stage, a beginning of arrest of development, but without reversion. This species retains many of the characters of the group of Gastri- oceras globulosum of the Carboniferous. Gephyroceras uchtense Keyserling, Upper Devonian, Russia. Figs. 9-11, adult stage. A primitive radicle, like the ancestor of the Meekoceratidae and Ceratitidae. Timanites acutus Keyserling, Upper Devonian, Russia. Figs. 12-14. A primitive Coniatite, a lateral branch of Gephyroceras, and the probable ancestor of the Hungaritidae and of the Sage- ceratidae. Figs. 1-8, from Hyatt and Smith, Triassic Cephalopod Genera of America. Figs. 9-12, from E. Holzapfel, Die Cephalopoden des Domanik im siidlichen Timan. Mém. Com. Géol. (St. Petersbourg), Vol. XII, No. 3. 1899. Puate ILI. } oe et, Jt ; | ; A ep ii a + Ay an ¥ ae ee +e att PuatTeE IV. Columbites parisianus Hyatt and Smith, Lower Triassic, Idaho. Figs. 1-3, adult stage. Figs. 4 and 5, adolescent stage, diam. 10 mm., corresponding to Gastrioceras. Figs. 6 and 7, easily adolescent stage, diam. 1.75 mm. Figs. 8-10, embryonic and early larval stages. Columbites shows a transition from the group of Gastrioceras towards the Tropitidae. Tropites subbullatus Hauer, Upper Triassic, California. Figs. 11-13, adult stage. Figs. 14-15, adolescent stage. Figs. 16-21, larval stages, showing development from the Goniatite to the Ammonite stage, with very unequal acceleration, ‘‘tele- scoping’’ of characters and stages. Columbites is the Lower Triassic ancestor of the Tropitidae, and connects that family with the Paleozoic ancestors, Glyphioceratidae. All figures on this plate are from Hyatt and Smith, Triassic Cephalo- pod Genera of America, Prof. Paper No. XL, U. 8. Geological Survey, 1905. ‘ . Puats LV, PLATE V. Discotropites sandlingensis Hauer, Upper Triassic, California. Figs. 1-4, adult stage, showing ornamentation and septa. Figs. 5-7, larval stage, diam. 5.5 mm., showing beginning of keel. Figs. 8-10, larval stage, diam. 4.25 mm., showing beginning of serra- tion of lobes, and transition from Goniatite to Ammonite stage. Figs. 11-13, early larval stage, diam. 2.68 mm., Goniatite stage, cor- responding to Gastrioceras. Paratropites Sellai Mojsisovies, Upper Triassic, California. Figs. 14-16, adult stage. Figs. 17-19, larval stage, diam. 5 mm., showing transition from Gon- iatite to Ammonite stage. Ceratites humboldtensis Hyatt and Smith, Middle Triassic, Nevada. Figs. 20-21, adult stage. Figs. 22-24, adolescent stage. Figs. 25-26, larval stage, diam. 8 mm. The three genera figured on this plate show convergence in different stocks. All figures on this plate are from Hyatt and Smith, Triassic Cephalo- pod Genera of America. PuatTE VI. Metasibirites Frecht Hyatt and Smith, Upper Triassic, California. Figs. 1-10, adult stage, showing arrest of development, reversion to the Goniatite stage, and many characters of genera that came between the primitive Goniatites and the more specialized Am- monites in the history of this stock. Leconteia californica Hyatt and Smith, Upper Triassic, California. Figs. 11-13, adult stage, showing arrest of development, and rever- sion to the primitive ancestral type. Figs. 14-15, larval stage, diam. 2.5 mm. Homerites semiglobosus Hauer, Upper Triassic, California. Figs. 16-21, adult stage, showing arrest of development, and rever- sion toward the ancestral stock. Both Homerites and Metasibi- rites show a tendency to develop a rudimentary keel, probably as a convergence phenomenon. Paragandes californicus Hyatt and Smith, Upper Triassic, California. Figs. 22-26, adult stage, showing arrest of development, and rever- sion to the Goniatite characters. All figures on this plate are from Hyatt and Smith, Triassic Cephalo- pod Genera of America. PuaTe VI. 22] '23] 2h: Puate VII. Meekoceras mushbachanum White, Lower Triassic, Idaho. Figs. 1-5, adult stages, showing development towards Ceratites. Meekoceras gracilitatis White, Lower Triassic, Idaho. Figs. 6-12, showing development from early stage to maturity. Both species are primitive forms, intermediate between the Goniatite | ancestry and the Ceratitic pesterity. Both are intermediate in characters between the Paleozoic and the Mesozoic types. All figures are from Hyatt and Smith, Triassic Cephalopod Genera of America. Puate VII. ROL os cael F = 3 § = Py ew tid ER as Puate VIII. Arpadites Gabbi Hyatt and Smith, Upper Triassic, California. Figs. 1-10, showing development from late larval stage to maturity, and reversion at maturity to some of the ancestral Meekoceras characters. Gymnotropites californicus Hyatt and Smith, Upper Triassic, California. Figs. 11-13, showing convergence with Discotropites and Eutomo- ceras. Beyrichites rotelliformis Meek, Middle Triassic, Nevada. Figs. 14-23, showing development from late larval stage, and partial reversion at maturity to the ancestral Meckoceras characters. This species also shows convergence with Ptychites, an entirely different stock. All figures from Hyatt and Smith, Triassic Cephalopod Genera of America. Puate VIII. PLATE IX. Aspenites acutus Hyatt and Smith, Lower Triassic, Idaho. Figs. 1-4, adult stage, showing resemblance to the Devonian Tim- anites. Eutomoceras Laubei Meek, Middle Triassic, Nevada. Figs. 5-7, showing convergence of Hungaritidae with Tropitidae. Inyoites Oweni Hyatt and Smith, Lower Triassic, California. Figs. 8-13, showing convergence of Hungaritidae and Tropitidae. Longobardites nevadanus Hyatt and Smith, Middle Triassic, Nevada. Figs. 14-16, showing convergence of Pinacoceratoidea with Hungar- itidae, through partial reversion towards the same ancestral Timanites. All figures from Hyatt and Smith, Triassic Cephalcpod Genera of America. PuaTEe LX. use PLATE X. Neolobites Choffati Hyatt. Fig. 1, showing arrest of development and reversion of a Cretaceous genus to the Paleozoic Goniatite stage. Heterotissotia neoceratites Peron, Upper Cretaceous, Peru. Figs. 2-4, convergence with the Triassic Ceratites, by reversion to some ceratitic ancestor, though probably not Ceratites. Ceratites semipartitus v. Buch, Middle Triassic, Germany. Fig. 5, septa for comparison with the ‘‘Pseudoceratites’’ of the Cretaceous. Otoceras Woodwardi Diener, Lower Triassic, India. Fig. 6 and 7, a transitional Permian and Lower Triassic genus, to show hetercchronous convergence with some of the ‘‘Pseudo- ceratites’’ of the Cretaceous. Paratissotia serrata Hyatt, Upper Cretaceous, Peru. Figs. 8-10, a Cretaceous genus, arrested in development, and show- ing atavistie reversion to characters very like those of Otoceras of the Permian and Lower Triassic. Sphenodiscus Hilli Hyatt, Upper Cretaceous, Texas. Fig. 11, septa, showing resemblance to Arcestidae of the Triassic, though probably not indicating relationship. Waagenoceras Hilli Smith, Permian, Texas. Fig. 12, septa, showing resemblance to those of Spenodiscus of the Cretaceous—a case of heterochronous convergence. Figs. 1, 8, 9,10, 11, from Hyatt, Pseudoceratites of the Cretaceous. Figs. 6 and 7, from Diener, Cephalopoda of the Lower Trias. Mem. Geol. Survey, India, 1897. Figs. 2-5, from Steinmann, Probleme der Ammoniten-Phylogenie. Sitz. Niederrhein. Gesell. Bonn, 1909. Fig. 12, from J. P. Smith, Carboniferous Ammonoids of America. PrAatre xX. Puate XI. Ussuria Waageni Hyatt and Smith, Lower Triassic, Idaho. Figs. 1-14, showing development from larval stage to maturity. A primitive progressive form, showing simple recapitulation of its ancestral history. Paranannites aspenensis Hyatt and Smith, Lower Triassic, Idaho. Figs. 15-20. Primitive Ammonite, transitional from the Paleozoic Glyphioceratidae to the Mesozoic Ptychitidae, an example of a radicle of a group. All figures from Hyatt and Smith, Triassic Cephalopod Genera of America. : aT t a 5 ae } iT ial 1 , i a =) iy Ue ” Hi ya wae) mal ia mee id } { ae } Ny oa Ff , F : i? 6 , a ( id ‘ is” T ‘few gua pod" pt 1 ae : : ay j - é VEE ate AY PuatTe XII. Cordillerites angulatus Hyatt and Smith, Lower Triassic, Idaho. Figs. 1-8, development from larval stage to maturity. A primitive Ammonite, showing simple recapitulation; a very perfect repe- tition of phylogeny in ontogeny. Pronorites cyclolobus Phillips, Lower Carboniferous, England. Fig. 9, showing development of the septa. The three species of Pro- norites illustrated are examples of the ancestral stock of Cor- dillerites and Medlicottia. Pronorites mizxolobus, Carboniferous, England. Fig. 10, septa, for comparison with P. cyclolobus. Pronorites cyclolobus, var. arkansasensis Smith, Lower Carboniferous, Arkansas. Figs. 11 and 12, shell and septa. Figs. 1-8, from Hyatt and Smith, Triassic Cephalopod Genera of America. Figs. 9-12, from J. P. Smith, Carboniferous Ammonoids of America. Puate XII. ie i a7. : ‘i tk. er i PuATE XIII. Baculites chicoensis Trask, Upper Cretaceous, California. Figs. 1-9, larval stages, showing coiled young, and derivation from the normal genus, Lytoceras. Lytoceras alamedense Smith, Upper Cretaceous, California. Figs. 10-15. Larval and adolescent stages, showing resemblance to young of Baculites. Schloenbachia oregonensis Anderson, Upper Cretaceous, Oregon. Figs. 16-21, larval and adolescent stages. Placenticeras pacificum Smith, Upper Cretaceous, California. Figs, 22-28. Larval and adolescent stages, showing recapitulation of phylogeny in ontogeny. Lytoceras, Schloenbachia, and Placenticeras belong to wholly different stocks, with different ancestry; and yet their young stages are very much alike, due to adaptation and not atavism. All figures are from J. P. Smith, figs. 1-9, Larval Coil of Baculites, American Naturalist, 1901; figs. 10-15, The Development of Lytoceras and Phylloceras, Proce. Calif. Acad. Sci., 1898; figs. 16-21, Larval Stages of Schloenbachia, Journal of Morphology, 1899; figs. 22-28, The Develop- ment and Phylogeny of Placenticeras, Proc. Calif. Acad. Sci., 1900. PLATE XIII, PLATE XIV. Fig. 1. Orthoceras timidum. Fig. 2. Cyrtoceras corbulatum. Fig. 3. Cyrtoceras Murchison. Fig. 4. Gyroceras alatum. Fig. 5. Nautilus planotergatus. Fig. 6. Lvituites lituus. Fig. 7. Bactrites (protoconch). Fig. 8. Mimoceras compressum. Fig. 9. Tropites phoebus. Fig. 10. Lytoceras Inebigi. Fig. 11. Crioceras Emerici. Fig. 12. Turrilites catenatus. Fig. 18. Baculites compressus. Fig. 14. Macroscaphites Ivan. All figures are from J. P. Smith, Evolution of Fossil Cephalopoda, Chapter IX, in D. S. Jordan’s Footnotes to Evolution, 1898. They illus- trate various stages in the evolution of Cephalopoda mentioned in the text. PLATE XIV. —— ‘ WAS ‘\\ \\\' 13 DT) WA ZA, y Wy YY Wy Wy) y YY UY LDDs BELA Z hhy ; JMS BELL Wp j LLLL ILL LLEOLE CEG LEE ALLL LLLAELLLLL ELLE BOERS ws ao at Ne a ¢ + : ~ 2 gE ee — ’ j i. a Gee ; - pe 2 . : Z J = owe ‘ ce : ' . 7 ha — > PLATE XV. Cliomtes (Traskites) robustus Hyatt and Smith, Upper Triassic, Cali- fornia. Figs. 1-8. A form arrested in development, and partly reversionary to Trachyceras. Clhiomtes (Californites) Merriami Hyatt and Smith, Upper Triassic, Cali- fornia. Figs. 9-12. A form more retarded than C. robustus, and showing more of the ancestral characters. Reversionary, by arrest of de- velopment, to Tirolites, in everything but the retention cf the trachyceran furrow. Trachyceras duplex Mojsisovies, Upper Triassic, Alps. Figs. 13-16. A progressive form, but showing the beginning of ar- — rest of development in the prolongation of the ontogeny, and persistence of the Tirolites stage in adolescence. Clionites (Neanites) californicus Hyatt and Smith, Upper Triassic, Cali- fornia. Figs. 17-20. Reversionary by arrest of development to the ancestral type, Tyrolites, but still showing the trachyceran furrow in- herited from its intermediate ancestor Trachyceras. Figs. 1-12, and 17-20, from Hyatt and Smith, Triassic Cephalopod Genera of America. Figs. 13-16, from E. von Mojsisovies, Das Gebirge um Hallstatt, II, 1893. RRA. & hE i aa 4 % syle ; s : ; i a : oe pee gaa’ LT TELE: : FES: B : ; SSE! : ‘ asses eer ers hare!