258 



A. Tlio costal pits of" the lateral margins narrow; posterior 

 marginals deeply notched above for the ribs: 



Surface smooth O. i^latylomas. 



AA. Lateral costal pits round ; the jjosterior marginals 

 deeply notched above for the riljs: 

 Surface smooth ; lateral marginals low, depressed . . . . O. sointus. 

 Surface coarsely pitted; lateral marginals elevated. . - . O. crosus. 

 AAA. Lateral costal pits round ; the posterior marginals 

 with upper face produced above the rib-pits, con- 

 cealing them ; 

 External border openly notched O. emnrginatus. 



OSTEOPYGIS PLATYLOMUS, Cope. 



Extinct Datracliia and Ei>iitilia nf Ninth Aniorica, 1H70, j)]). 135,235. 



Greensand, No. 5, of New Jersey. 



OSTEOPYGIS SOPITUS, Leidy. 



C/ic(oHe sojji'/rt, Leiily,Crotaoeons Reiitiles of Nm-tli Auiorica, It^fiS, i). 104 ; Prophiira soplla, 

 Cope, Extinct Batrachia and Rcptilia of North America, l.'^TO, 110, Plato VII, lig. 4. 



Grreensand, No. 4, of New Jersey. 



OsTEOPYGIS EROSUS, Cope, sp. IIOV. 



The largest species of the genus is represented !)y many specimens from 

 the upper bed of greensand of New Jersey. Although exceeding the O. 

 emarginatus in size, the posterior marginals do not present as high a degree 

 of ot^sification of the interior border. These bones are thin and Hat, while 

 the laterals are very massive, aud have an elevated outer lamina, much exceed- 

 ing the corresponding ones of O. sopitm in this respect, and in transverse 

 diameter below, although tiiey equal them in length. Tlu- pit for the fir.^t 

 costal is at the posterior end of the second margiiial. This, with the first 

 marginal, is coossified to the carapace, as are the pygal and eleventh mar- 

 ginals. The vertebral bones are more than twice as long as wide; are slightly 

 notched before, and obtusely rounded at the narrowed posterior end. The 

 grooves of the dermal scuta are everywhere deeply impressed in this species, 

 and the surface of all the bones marked by numerous pits resembling rain- 

 drop marking, which are somewhat irri-gular in their depths, and not as 

 sharply defined as in most of the f()ssi! Trio/n/chcs. 



