346 0. C. Marsh— Vertebrate Infe in America. 
the Mosasaurs. A few fragmentary remains have indeed been 
referred to these genera, but the determination may fairly be 
questioned. This is more than true of the proposed new order 
Streptosauria, ich, was founded wholly on error. The order 
lestosaurta, however, is well represented, but mainly by forms 
more nearly related to the genus Pliosaurus than to the type 
of the group. These were marine reptiles, all of large size, 
while some of them attained vast dimensions. So far as at 
present identified, they may be referred to the genera, Cimolio- 
saurus, Discosaurus (Llasmosaurus), and Pliosaurus. e num- 
ber of species is comparatively few, and none are known above 
the Cretaceous. The important suggestion of Gegenbaur, that 
the Halisauria, which include the Plesiosaurs, branched o 
from the Fishes before the Amphibians, finds some support in 
American specimens recently discovered. 
The Reptiles most characteristic of our American Cretaceous 
strata are the Josasauria, a group with very few representatives 
in other parts of the world. In our Cretaceous seas, they ruled 
supreme, as their numbers, size, and carnivorous habits, enabled 
them to easily vanquish all rivals. Some were at least sixty 
feet in length, and the smallest ten or twelve. In the inland 
retaceous sea from which the Rocky Mountains were begin- 
ning to emerge, these ancient “Sea Serpents” abounded; an 
many were entombed in its muddy bottom. On one occasion, 
as _I rode through a valley washed out of this ad ocean bed, I 
saw no less than seven different skeletons of these monsters in 
sight at once. ‘ osasaurs were essentially swimming Liz- 
ards, with four a developed paddles, and they had little affin- 
ity with modern serpents, to which they have been compared. 
The species are quite numerous, but they belong to compara- 
tively few genera, of which Mosasaurus, Tylosaurus, Lestosaurus 
and Adestosaurus, have alone been identified with certainty. The 
genus Mecasnaten was first found in Europe. All the known 
species of the group are cases us. 
The Crocodilia are abundant in rocks of Cretaceous age in 
dere, and two distinct types are represented. The older 
type, which is foreshadowed by Belodon of the Trias, has bicon- 
cave vertebre, and shows marked affinities with the genus 
Teleosaurus, from the Jura of Europe. The best known 
tg is Hyposaurus, of which there are several species, all 
ore or less resembling in form the modern Gavial of the 
Sane peculiar intermediate form is seen in Diplosaurus, 
te ite Wealden of the Rocky Mountains. The second type, 
which now makes its appearance for the first time, has pro- 
ecelian vertebree, and in other respects resembles existing Croc- 
odiles. The genera described are Bottosawrus, Holops and Tho- 
racosaurus, none of which, so far as known, pass above the 
