VERTEBRATE LIFE IJY AMERICA. 517 



impossible. No one who has tasted such waters, or has attempted to 

 ford one of the modern alkaline lakes which 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 very 

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

 Cyprinoids, related to the modern 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 sufficient, 

 I trust, to give an outline of its history. Of this history, it is evident 

 that we have as yet only a very imperfect recond. 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 as to clearly indicate for the class a much earlier 

 origin. In this connection, 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 knowledge 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 ex- 

 istence. 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 Lepidotus of the Creta- 

 ceous, and perhaps on through the Triassic Ischypterus and Carbo- 

 niferous Palceoniscus ; but beyond this, in our rocks, it is lost. The 

 living Chimcera 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 Rhynchodus. Our sharks 

 likewise can be traced with some certainty back to the Palaeozoic ; 

 and even the Lepidosiren, of South America, although its immediate 

 predecessors are unknown, has some peculiar characters 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 forms of 

 the latter have been considered by anatomists as belonging to this 

 group. The earliest evidence of Amphibian existence, on this conti- 

 nent, is in the Sub-Carboniferous, where footprints have been found 

 which were probably made by Labyrinthodonts, the most ancient 

 representatives of the class. Well-preserved remains are abundant 



