38 FOSSIL TURTLES OF NORTH AMERICA. 
In North America no turtles are known to have existed in deposits below the 
Morrison beds of the Upper Jurassic. Dr. Edward Hitchcock has indeed assigned 
to the tortoises certain tracks observed by him in the Triassic sandstones of Massa- 
chusetts and Connecticut; but, while there is no improbability that turtles occurred 
there and then, there is no certainty of it. As is seen from table 1, 2 species of 
turtles, both belonging to the Amphichely dia, have been found in the Mowncon beds 
of the Rocky Mount: un region. ‘hese beds are sometimes regarded as belonging to 
the Lower Cretaceous, equivalent to the Wealden of Europe, Bad it is more probable 
that they correspond to the Kimeridge Clay or the Purbeck (Fraas, Zeitschr. deutch. 
geol. Gesellsch., Litt, 1902, briefl. Mitth., p- 59) or even a little lower. So far as now 
aor n, no other group than the Amphichelydia are represented until we reach the 
Benton, of the Upper Cretaceous. I[n the lowest division of this there occurs an 
undoubted marine turtle belonging to the Cryptodira. A species of Glyptops is 
found in the Potomac beds near Washington, District of Columbia, and another 
species of probably the same genus in the Washita beds of Kansas. 
‘Turtle remains are not uncommon in the Niobrara beds of Kansas, but when we 
come to examine the list, we find the species not numerous, and they belong to only 
four genera. The species of Toxochelys and of Porthochelys z appear to have lived in 
the Niobrara ocean near the coasts. The species of Protostega, on the other hand, 
evidently ventured far out on the high seas. Toxochelys and Porthochelys appear to 
have continued on into the Pierre; Pecionte ga was there replaced by, or transformed 
into, the huge Archelon. 
About the middle of the Upper Cretaceous, conditions were favorable for the 
existence and the inhumation of many species of turtles. These are found now in 
two widely removed regions and in deposits made under widely different conditions. 
On the Atlantic border, especially in New Jersey , occurs a series of marine deposits 
from which have been derived about 40 species of turtles, including g species 
of Pleurodira and 2 species of Trionychidaw. The remainder are Cry ptodira, among 
them many coast-inhabiting Thalassemydidz, all of which were probably furnisht 
with jaws fitted for crushing hard mollusks and crustaceans. The family of Dermate- 
mydide, represented now by only 3 genera and 4 species, appear in great numbers 
and variety, especially in the New Jersey Cretaceous greensand. Whence this 
assemblage of turtles came we have no clue. Scant remains indicate the existence 
of two species of large marine turtles, 4tlantochelys and Neptunochelys. 
In the heart of the continent at nearly the same time, possibly a little earlier, 
there were being laid down fresh and brackish water deposits, now known as the 
Judith River beds. They are found in Montana and British America, and have 
furnisht about 15 species of turtles; but these are quite different from those of the 
Atlantic coast deposits just mentioned. ‘There are, indeed, 4 or 5 species of triony- 
chids of the genus A spideretes, a genus living now in Asia, a species of Plastomenus, 
and 3 or 4 species of Dermatemy didz:; but che latter belong to genera distinct from 
uhese found in the New Jersey deposits. In these Judith River beds reappear rep- 
resentatives of the Amphichely dia, turtles which we have found to characterize the 
Upper Jurassic and the Lower Cretaceous. In America the turtles of this group 
appear generally to have avoided true marine conditions. 
Succeeding the Pierre and the Fox Hills epochs came that of the Laramie. In 
the fresh and brackish water deposits laid down during this time there were buried 
remains of a great variety of turtles, but inforainately these remains are usually 
very fragmentary; 16 species are recognized as belonging here. Their relationships 
are close to the turtles of the Judith River beds, some species being as yet undis- 
tinguishable. The conditions under which the two deposits were laid down were so 
