AND AYES OF NORTH AMERICA. 



125 



timatc marginal, joins a superior angle of the antepenult. The superior margin of the penultimate is straight, and 

 but little elevated above the caudal pair. From this increased width of the last vertebral, its lateral suture is 

 more Oblique, and what remains of the lateral suture of the penultimate vertebral is still more oblique, indicating 

 a still wider senium. The posterior vertebral bone is a little more elongate than in several individuals of C. clausa. 



The posterior margin is not recurved, but is vertical, and therefore from a female animal. There are no em; r 

 ginations or processes. On the inferior aspect, the concavity which receives the crest, of the ilium is deeper and 

 nearer the margin than in C. clausa. 



This species was found by Samuel 1?. Harrison, M. D., of Easton, Md., on Oxford Neck in Talbot Co., Mary- 

 hmd, in connection with postpliooene fossils, as follows: Elephas amerioanus, Ccrvus canadensis, Cariacus virginianm, 

 Chelydra serpentina. 



Remains of a Cistudo occur in the postpUocene bone breccia, of eaves in S. W. Virginia, but whether they belong- 

 to C. clausa or some other species is not as yet determined. 



EMYS, Brongniart. 



The only species of this genus which I have had the opportunity of studying are the 

 Hi ret; (i)llowing from the cretaceous green-sand of New Jersey. They agree in the mas- 

 sive thickness and dense structure of plastron and carapace, which peculiarity suggests 

 doubt as to their aquatic habitat, and enquiry as to whether they may not have been 

 inert; or less terrestrial. Their reference to Emys is provisional, as the limbs, cranium 

 and caudal marginal scute arc; unknown. In E. petrosus the heads of the posterior ribs 

 are rudimcntal as in Adocus. 



The species may be distinguished as follows: 



Sutures of hyo-and hyposternal bones, coarse and ragged; hyostcrnal nearly twice as 

 thick anteriorly as posteriorly; eighth marginal acute edged, its width 11-12 length hyos- 

 ternal, its depth 5-4 the same. 



E. FIRMUS. 



Sutures minutely rugulose, byosternal thicker anteriorly; eighth marginal with thick 

 obtuse edge, depth 15-4 length byosternal, its width .55 same ; superior plane of byoster- 

 nal transversely as wide as a costal, inferior plant- very convex; mesosternum width .66 

 length of do.; size medium. 



E. PETROSUS. 



Sutures minutely rugulose; byosternal thickest posteriorly, its inferior face plane, 

 superior plane twice as wide as a, costal; width of mesosternum 6—7 length, and width of 

 eighth marginal .05 length of same; size smaller; 



E. TURGIDUS. 



AMERI. I'll 1 1.0SO. SOC. — VOL. XIV. 32 



