88 THE FOSSIL REPTILES OF NEW JERSEY. 
other orders in the number of species. "There have been 
twenty found in the Cretaceous of New Jersey, and three 
additional ones are known from the Tertiaries of the same 
State. The Cretaceous turtles may be arranged under four 
heads, viz., true Emydes or fresh water forms ; Chelydrine 
Emydes, or snappers; Trionychide or soft shells; and Hy- 
draspidide, a type now confined to the Southern Hemisphere, 
which throw the head round the side of the shell, instead of 
drawing it in. It will be observed that all of these forms 
occur at the present day in fresh water only, and that true 
marine turtles are not found in this part of the Cretaceous 
formation. Add to this the fact that the crocodiles are rather 
estuary and river animals; that the Dinosaurs are terrestrial ; 
and that by far the most abundant shells of the same region 
are oysters and Exogyre, and we have indicated a condition 
of occasional separation from the high ocean, by seaward 
bars and islands, or even by occasional considerable strips 
of dry land. 
The Emydiform turtles all belong to the genus Adocus of 
Cope, and were often of the size of our bitte gulf species, 
but generally of far more massive structure. The snapper- 
like forms are more numerous; they have been taken to be 
marine types, and indeed their fore-limbs appear to have been 
_ more paddle-like than those of the species of our modern 
rivers. They are represented by nine species, which per- 
tain to five genera. These forms differ much in the relative 
union of the shield of the carapace, and its marginal pieces. 
In the genus Peritresius of Cope, the margin was largely 
separate, and the shell covered by a thin Td ; in Lytoloma 
pe the margin was also distinct, except in front and rear; 
and the carapace was covered by heavier shell-like dermal | 
plates. Propleura Cope contained one large species— P. 
sopita, where the margin was broad and flat, and free as in 
the last, except that it had a broad union with the disc in 
front. Finally Osteopygis Cope, was solidly knit fore and 
aft 
by suture between disc and margin. Of its three species, E 


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