150 



THE EXTINCT BATRACIIIA, REETILIA 



The broad, regular alveolar surfaces have no doubt supported a massive corneous table, in some degree like that 

 of Platypeltis ferox, and with little or no external cutting margin. This arrangement, as well as the compactness 

 of structure, are appropriate to a nutrition dependent on crushing more or less hard bodies, as molluscus. That the 

 Ostreae, Tercbratulae, etc., of the sea coasts or estuaries in which it lived formed much of its food, is therefore quite 

 probable. 



Estimating the proportions to have been similar to those of Chclydra serpentina,* the dimensions of the Euclas- 

 tes platyops were — ■ — 



Length from end muzzle to end tail, 

 " of carapace, 



Ft, In. 



8 K». 



2 8.5 



This species belongs most probably to one of the genera of the same type here de- 

 scribed, but whether to Peritresius, Propleura or Osteopygis, is not as yet ascertainable. 

 In any ease, Euclastes is an older name than either of the above. 



PERITRESIUS, Cope. 



This genus is proposed to express the characters of the Chelone or n at a of Leidy. 



Nothing is known of the species but a costal and parts of two adjacent marginal bones. 

 These are covered with coarse tubercles, as in some Trionyx, and more as in Prochonias 

 nod os us. There arc no dermal sutures on the specimens, and. it is not probable that 

 the dermal covering was corneous or scutiform. The pit for the rib is very small and flat, 

 and not at all as in Chelone. Were it not that the head of the rib is not so flattened as 

 in Trionychidae, I should imagine the genus might be allied toEmyda,or the Trionyches, 

 with marginal bones. With our present knowledge, it is better that the costal bone should 

 remain near Peritresius. 



The structure of the costal bone above the interior or costal layers is vesicular. The 

 entire freedom of the marginal bone separates the form from any of our known Pleurodira. 



PERITRESIUS ORNATUS, Leidy. 

 Cltelone omnia, Leidy, Proc. A. N. Rci., 1850, 303 Cretaceous Kept., 1. c. 



Marginal bones, covered with coarse tubercles in the middle, and coarse ridges near the sutures, which are wider 

 than the intervals between them. 



New Jersey. 



TRIONYCHIDAE, 



Seven species of this family have been found in the North American strata, all 

 referable to 



* Compared Inapporttely with ttydraipti maximiU<ml\n the original description. 



