AND AVES OF NORTH AMERICA. 



233 





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. vyomrngensis described by Leidy, and 

 in a specimen of A. beatus, noticed by me in Synopsis Batr. Rept. N. A., j>. 139. I there state that it is emarginate, 

 an error consequent on a certain assyinetry 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 narrow by reference to my figure of A. pectoralis (Syn. Hat. 

 Kept., N. A., Tab. VII, fig. 1,) or Leidy's ftgure of A. pravns, Cretac. Rept. N. Am. XIX, fig. 1. in the nearly 

 perfect specimen of A. vyomingenaia, 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 shell, especially of the plastron. A. pectoralis is the 

 stoutest as well as the smallest; A. pravus and A. agilis arc; the thinnest, the latter the largest of the genus. No 

 porl ions can be certainly ascribed to the crania of this genus. 



In specimens of A. agilis, A. pravus and A. beatus, the longitudinal median suture of the plastron presents 

 much irregularity from the union of the alternating bones across the point of meeting of four, by an oblique portion 

 of the suture. 



Thickness of liyosternals less than four lines in the transverse extent of same; intermarginals short; mesosterna 

 prolonged posteriorly, smooth below; small. A. pectoralis. 



Thickness of hyostemals one-eighth transverse extent of same; above with sightly impressed dots or delicate 

 grooves, closely placed; larger, vertebral bones wider. A. beatus. 



Sternum thick; vertebral bones narrower; carapace more coarsely longitudinally impressed grooved; mesosternum 

 deeply received; lateral intermarginals elongate. A. vyomingenaia. 



Plastron quite thin; nicsosiernal deeply received in the liyosternals. A. pravus. 



Plastron quite thin; mesosternal occupying an open concavity of the liyosternals; surface everywhere delicately 

 impressed punctate and grooved; Intermarginal scuta very long and narrow. A. agilis. 



Adocus pectoralis, Cope. 



Pleurosternum peetorale, Dope, Proo. Ac. Nat. Sci. Phila., 1808, 2!5(S; Trans. Amer Philos. Soe. XTV, 1800, 100, Tab. 



VII. fig. 1. 



Indicated by a, pair of perfect hyosternal bones from the upper Cretaceous marl bed, near Medford, Burlington 

 Co., N. J. 



Adocus beatus, Leidy. 



Emya beatus, Leidy. Cretaceous Reptiles. N. Amer. p, 107, Tab. XVIII, fig. 1-3. Adocus beatus, Cope, Proc, A. 



N. S., Phila,, 1808, 285. Geological Survey, N. Jersey, App. 0, p. 174. 



Not uncommon. If is considerably less stout than the preceding. The edges of the posterior lobe of the plastron 



are thinned out by a, submarginal groove. As in other Emydoids there is a, marked concavity for each pubic b( 



The suture between the hyo- and hyposternal bones is less interlocking than in A. agilis, and less line than in A. pec- 

 toralis. I have suggested that it may have possessed a slight mobility in life. Its free is longitudinally grooved in 

 the hyposternal, and a corresponding convexity of 11 ic face of the hyosternal fits it. In a specimen from Medford, 

 N. .1., the posterior lobe is 5 in. lin, long, and 5 in. 8 lin. wide at the marginal notches. Hyosternal of nearly equal 

 thickness, medially 7 lines. 



Adocus vyomingensis, Leidy. 



Emyt vyomingenaia, Leidy, 1'roc. Ac. Nat. Sci. Phila., 1800, p. 00. Baptemys vyomiitgensis, Leidy, loc. cit. 1870, 



January. 



Best known from an almost complete specimen consolidated by the contained mass of mineral, 'there are three 

 interinarginal bones, of which the middle one is more elongate than the others. There is a weak carina, on some of the 

 AMERI. PHILO. SOC. — Vol,. XIV. — 50. 



