Sept. 20, 1877] 



NATURE 



449 



Chemung epoch the great dipterian family was introduced with 

 Diflcriis, Heliodiis, and possibly Ceratodus. Species of the 

 European genera, Bothriolepis and Holoptychuis, have likewise 

 been found in our Devonian deposits. 



With the close of the Devonian came the almoct total extinction 

 of the great group of placoderms, while the elasmobranchs, 

 which had hitherto occupied a subordinate position, increase in 

 numbers and size, and appear to be represented by sharks, rays, 

 and chimeras. Among the members of this group from the 

 carboniferous were numerous cestracionts, species of Cocltliodiis 

 of large size, with others of the genera Deltodus, Ilelodus, 

 Psammodiu, and Sandalodiis. Of the Petalodonts there were 

 AntUodtis, Chomatodiis, Ctenoplychius, Petalodus, and Pelalo- 

 rhyiichus ; and of the hybodonts, the genera Cladcdus, Cair/ia- 

 ropiu, and Diplodus. These elasmobranchs were the rulers of 

 the carboniferous open sea, and more than one hundred species 

 have been found in the lower part of this formation alone. The 

 ganoids, although still abundant, were of smaller size, and 

 denizens of the more shallow and confined waters. The latter 

 group of fishes was represented by true lepidostid.-e, of the 

 genera PahTonisnis, AmMyptci lis, Platysomus, and Eiirylepis. 

 Other genera are, Rliizodiis, Megalichtliys, Ctaiodus, Edcstus, 

 Orodiis, Ctenacaiitkns, Gyracanthus, and CiHacanthus. Most of 

 these genera occur also in Europe. 



From the permian rocks of America no vertebrate remains ore 

 known, although in the same formation of Europe ganoids are 

 abundant, and with them are remains of sharks, and some other 

 fishes, the affinities of which are doubtful. The pal.Tozoic fishes 

 at present known from this country are quite as numerous as 

 those found in Europe. 



In the mesozoic age the fishes of America begin to show a 

 decided approach to those of our present waters. From the 

 triassic rocks ganoids only are known, and they are all more or 

 less closely related to the modern gar-pike, or Lepidostcus. They 

 are of small size, and the number of individuals preserved is very 

 large. The characteristic genera are Catopterus, Ischypterns, Ply- 

 choUpis, Rhabdolepis, and Tufieodits, From the Jurassic deposits 

 no remains of fishes are known, but in the cretaceous ichthyic life 

 assumed many and various forms ; and the first representatives of 

 the teleosts, or bony fishes, the characteristic fishes of to-day, 

 make their appearance. In the deep open sea of this age elas- 

 mobranchs were the prevailing forms, sharks, and chimreroids 

 being most numerous. In the great inland cretaceous sea of 

 North America true osseous fishes were most abundant, and 

 among them were some of carnivorous habits and immense 

 size. The more sheltered bays and rivers were shared by ihe 

 ganoids and teleosts, as their remains testify. The more com- 

 mon genera of cretaceous elasmobranchs were Olodiis, Oxyrhina, 

 Cahocerdo, Lamua, and Plychodiis. Among the osseous fishes, 

 Bc'ryXy pjichodus, Portheus and Sauroccphalns were especially 

 common, while the most important genus of ganoids was 

 Lepidotus. 



The tertiary fishes are nearly all of modern types, and from the 

 beginning of this period there was comparatively little change. 

 In the marine beds sharks, rays, and chim^eroids maintained 

 their supremacy, although teleosts were abundant, and many of 

 them of large size. The ganoids were comparatively few in 

 number. In the earliest eocene fresh-water deposits it is inter- 

 esting to find that the modern gar-pike, and Aiiiia, the dog-fish 

 of our western lakes, whicli by their structure are seen to be 

 remnants of a very early type, are well represented by species so 

 closely allied to them that only an anatomist could separate the 

 ancient from the modern. In the succeeding beds these fishes are 

 still abundant, and with them are siluroids nearly related to the 

 modem cat-fish [Pimdodiis). Many small fishes allied apparently 

 to the modern herrirg (Cliipca), left their remains in great 

 numbers in the same deposits, and with them has been recently 

 found a land-locked ray (Hdiobatis). 



The almost total absence of remains of fishes from the miocene 

 lake-basins of the west is a remarkable fact, and perhaps may 

 best be explained by the theory that these inland waters, like 

 many of the smaller lakes in the same region to-day, were so 

 impregnated with mineral matters as to render the existence of 

 vertebrate hfe in them impossible. No one who has tasted such 

 waters or has attempted to ford one of the modem alkaline lakes 

 whicli are often met with on the present surface of the same 

 deposits, will doubt the efficiency of this cause, or the easy 

 entombment of the higher vertebrates that ventured within 

 their borders. In the pliocene lake-basins of the same region 

 remains of fishes were not uncommon, and in some of them are 

 veiy numerous. These are all of modern types and most of them 



are cyprinoids related to the modem carp. The post-pliocene 

 fishes are essentially those of to-day. 



In this brief synopsis of the past ichthyic life of this continent 

 I have mentioned only a few of the more important facts, but suffi- 

 cient, I trust, to give an outline of its history. Of this history 

 it is evident that we have as yet only a very imperfect record. We 

 have seen that the earliest remains of fishes known in this country 

 are from the lower Devonian ; but these old fishes show so great a 

 diversity of form and structure a<: to clearly indicate for the class 

 a much earlier origin. In this eo inection we must bear in mind 

 that the two lowest groups of existing fishes are entirely without 

 osseous skeletons, and hence, however abundant, would leave 

 no permanent record in the deposits in which remains of fishes 

 are usually preserved. It is safe to infer from the know- 

 ledge which we now possess of the simpler forms of life, 

 that even more of the early fishes were cartilaginous, or so 

 destitute of hard parts as to leave no enduring traces of 

 their existence. Without positive knowledge of such forms, 

 and considering the great diversity of those we have, it 

 would seem a hopeless task at present to attempt to trace 

 successfully the genealogy of this class. One line, however, 

 appears to be direct, from our modern gar-pike, through the 

 lower eocene Lepidosteus to the Lipidotus of the cretaceous, and 

 perhaps on through the triassic Ischypteins and carboniferous 

 l^ahconiscus ; but beyond this, in our rocks, it is lost. The 

 living chimaera of our Pacific coast has nearly allied forms in the 

 tertiary and cretaceous, more distant relatives in the carboniferous, 

 and a possible ancestor in the Devonian Rhynchodiis. Our 

 sharks likewise can be traced with some certainty back to tlie 

 palaeozoic ; and even IheLtpidcsircii, of South America, although 

 its immediate predecessors are unknown, has some peculiar cha- 

 racters which strongly point to a Devonian ancestry. These 

 suggestive lines indicate a rich field for investigation in the ancient 

 life-history of American fishes. 



The amphibians, the next higher class of vertebrates, are so 

 closely related to the fishes in structure, that some peculiar foi ms 

 of the latter have been considered by anatomists as belonging to 

 this group. The earliest evidence of amphibian existence, on 

 this continent, is in the sub-carboniterous, where foot-prints have 

 been found which were probably made by labyrinthodonts, the 

 most ancient representatives of the class. Well preserved remains 

 are abundant in the coal-measures, and show that the labyrintho- 

 donts differed in important particulars from all modern amphi- 

 bians, the group which includes our frogs and salamanders. 

 Some of these ancient animals resembled a salamander in shape, 

 while others were serpent-like in form. None of those yet dis- 

 covered were frog-like, or without a tail, although the restored 

 labyrinthodont of the text-books is thus represented. All were 

 protected by large pectoral bony plates, and an armour of small 

 scutes on the ventral surface of the body. The walls of their 

 teeth were more or less folded, whence the name labyrinthodont. 

 The American amphibians known from osseous remains are all 

 of moderate size, but the foot-prints attributed to this group 

 indicate animals larger than any of the class yet found in the Old 

 World. The carboniferous amphibians were abundant in the 

 swampy tropical forests of that period, and their remains have 

 been found imbedded in the coal then deposited, as well as in 

 hollow stumps of the trees left standing. 



The principal genera of this group from American carboniferous 

 rocks, are, Sam-opus, known only from foot-prints, Baphelcs, 

 Doidrirpitoii, Hylonomus, Ilyhrpetoii, Raniccps, Pelion, Lepto- 

 phractus, Molgopkis, Plyonins, Amphihanius, Cocylinus, and 

 Ceraterpeton. The last genus occurs also in Europe. Certain 

 of these genera have been considered by some writers to be more 

 nearly related to the lizards {Laccrtilia) among true reptiles. 

 Some other genera known from fragmentary remains or foot- 

 prints in this formation have likewise been referred to the true 

 reptiles, but this question can perhaps be settled only by future 

 discoveries. 



No amphibia are known from American permian strata, but 

 in the triassic, a few characteristic remains have been found. 

 The three genera, Diciyoccphahis, Dispdor, and Pariostepis, have 

 been described, but, although apparently all labyrinthodonts, the 

 remains preserved are not sufficient to add much to our know- 

 ledge of the group. The triassic foot-prints which have been 

 attributed to amphibians are still more unsatisfactory, and at 

 present no important conclusions in regard to this class can be 

 based upon them. From the Jurassic and cretaceous beds of 

 this continent, no remains of amphibians are known. A few 

 only have been found in the tertiary, and these are all of modern 

 types. 



