576 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



This evidence is, however, of little weight, since that genus is the last 

 remnant of an ancient type, which dates not only from Mesozoic, but 

 also from Palaeozoic times. The immediate extinct allies of Lepidosteus 

 have not yet, it is true, been ascertained with sufficient accuracy. 



The results of the investigation into the Judith Kiver fauna are the fol- 

 lowing : — The genera are nearly all peculiar ; such as are not, excepting 

 Lepidosteus, having a range through Cretaceous and Tertiary time, as 

 Crocodilus, Trionyx, and Emys. Of the orders, besides those which every- 

 where range from Triassic or Jurassic through Tertiary time, there are 

 three exceptions. The one which is represented by the greatest abund- 

 ance of species and individuals, the Binosauria^ is Mesozoic, ceasing with 

 Cretaceous time. The ordinal position of the group I have called 

 Choristodera is somewhat uncertain; but its species must be withdrawn 

 from the Sauropterygia, where I have hitherto placed them. The division 

 is, so far, peculiar to the formation, and I suspect that the Ischyrosaurus 

 from the Fort Union beds of Dakota must be placed in it. The 

 CJioristodera are of Mesozoic cast in their relationship to the Rliyncho- 

 ceplialia; but one genus of this order persists until the present time in 

 New Zealand. Its Mesozoic character is therefore not so strong as is 

 that of the Sauropterygia. Thirdly, the Urodele Batrachia have been 

 chiefly found heretofore in the Tertiary formations. It is true that Pro- 

 fessor Gaudry has found two genera in the Coal-Measures of the Ehine, 

 which he regards as Urodela, but the structure of the skull of these ani- 

 mals is not sufficiently well ascertained to definitely settle this point.* 

 The value of the evidence derived from the Salamanders Scaplierpeton 

 and Eemitrypus cannot therefore be satisfactorily estimated at present. 

 The positive evidence then as to the age of the Judith River fauna is, 

 that it is Cretaceous, but, as might be supposed from its position, with 

 some Tertiary affinities. 



The stratigraphical evidence is moreover not opposed to this determi- 

 nation. Since the existence of extensive areas of fresh water on the sur- 

 face of the earth, the faunse of their shores have been those of the ages 

 that have preceded them. At the dlose of each great period, an eleva- 

 tion of the ocean bed has inclosed tracts of water which became fresh. 

 These elevations have not destroyed the terrestrial animals, so that the 

 remains preserved in these lakes have revealed to us the inhabitants of 

 the laud which probably existed during the preceding ages. On the 

 other hand, the inhabitants of the ocean have been lost in such, locali- 

 ties. The destruc'cion of the laud animals has followed at a later period. 

 Such is the conclusion to be derived from the determinations of European 

 geologists. Thus the Ooal-Measures suoeeided the deep-sea epoch of the 

 Subcarboniferous. This formation is a part of the Carboniferous, not of 

 the Trias. In the United States, a still higher bed closed the Carbonif- 

 erous, representing perhaps the Permian. It is characterized by pecu- 

 liar genera of Lizards, Crlcotus Cope, Clei)sydrops Gope,'^ Genitodus, and a 



* For a synopsis of the characters of the orders of Batrachia, see Paleontology of Ohio 

 vol. ii, p. 352. 



