Cope.] -^"^ [March 4, 



are very distinct in our specimeng, while I have seen it in only one of the 

 two or three in which the bridge is preserved in A. heatus. In A. pravus 

 I have not seen it, but the contracted entire xiphisternal elements pointed 

 out by Leidy are quite like those of A. beatus, to which it is indeed very 

 nearly allied. 



The narrowed form of the posterior lobe is best seen in the specimen of 

 A. wyomingensis described by Leidy, and in a specimen of A. beatus no- 

 ticed by me in Synopsis Batr. Eept. N. A. p. 129. I there state that it is 

 emarginate, an error consequent on a certain assymetry of the specimen, 

 and its fractured condition. In A. agilis it is apparently rather better 

 developed. 



~ The form of the anterior lobe is easily seen to be narrowly reference to 

 my figure of A. peetoralis (Syn. Bat. Rept. N. A.) Tab. VII fig. 1), or 

 Leidy's figure of A. pravus Cretac. Eept. N. Am. XIX fig. 1. In the 

 nearly perfect specimen of A. vyomingensu this portion is broken away, 

 but Leidy describes this portion of a specimen, which has the character of 

 the above species. 



The species differ much in the relative stoutness of their shells, especial- 

 ly of the plastron. A peetoralis is the stoutest as well as the smallest ; 

 A. pravus and A. agilis are the thinnest, the latter the largest of the 

 genus. No portions can be certainly ascribed to the crania of this genus. 



In specimens of A. agilis, A. pravus, and x\. beatus, the longitudinal 

 ttiedian suture of the plastron presents much irregularity from tlie union 

 of the alternating bones across the point of meeting of four, by an oblique 

 portion of the suture. 



Thickness of hyosternals less than four times in the transverse extent of 

 same ; intermarginals shorter; mesosternal prolonged posteriorly; smooth 

 below; small. a. pectokalis. 



Thickness of hyosternals one-eighth transverse extent of same; above 

 with slightly impi-essed dots or delicate grooves, closely placed ; larger, 

 Vertebral bones wider, A. beatus. 



Sternum thick ; vertebral bones narrower ; carapace more coarsely lon- 

 gitudinally impressed grooved ; mesosternal deeply received ; lateral in- 

 termarginals elongate. a. vyomingensis. 



Plastron quite thin ; mesosternal deeply received into hyosternals. 



A. PRAVUS. 



Plastron quite thin ; mesosternal occupying an open concavity of the 

 hyosternals ; surface everywhere delicately impressed punctate and 

 grooved ; intermarginal scuta very long and narrow. A. agilis. 

 Adocus pectokalis. Cope. 



Pleurosternum pectorale, Cope. Proc. Ac. Nat. Sci. Phila., 1868, 236 ; 

 Trans. Amer. Philos. Soc. XIV, 1869, 130 ; Tab. VII, fig. 1. 



Indicated by a pair of perfect hyosternal bones from the upper Creta- 

 eous marl bed near Medford, Burlington Co, N. J. 

 ADOCUS BEATUS, Leidy. 



Emys beatux, Cretaceous Reptiles, N. Amer. p. 107 Tab. XVIIT, fig. 

 1-3. Adocus beatus, Cope, Proc. A. N. S., Phila., 1868, 235. Geologi- 

 cal survey, N. Jersey, App. C. p. 734. 



