AND AVES OF NOKT1I AMERICA. 



135. 



I. The margins of the posterior marginal plates continuous, either notched or even 

 medially. 



a The rib-fossae of the marginals flat; ?no nuchal senile. 



Upper margin of inner face of (7th and 8th) posterior marginals much produced; 

 lower margin not prolonged. Lower margin of 5th and 6th marginals not projecting, 

 their inner face vertical. Outer face of narrow marginals convex or little concave 1 , their 

 scuta l.f long as wide. Eighth marginal \ wide as long. PLATYLOMUS'. 



aa The rib-fossae of the lateral marginals cylindric; a nuchal scute. 



Upper and lower margins 7th marginal both prolonged ; lower margin 5th very much 

 produced inwards giving a horizontal inner, as well as outer face; outer face of narrow 

 marginals concave except the anterior; scuta of latter 1| long as wide; 9th marginal ' (; : ' 

 wide as long; 5th marginal nearly .75 wide as long. EMARGINATUS. 



II. Margins of the posterior marginal plates acuminate medially. 



Posterior lateral bones short, wide, width greater and length, pit round, margin 

 strongly repand; anterior laterals less confluent with disc, strongly concave on outer face. 



CHELYDIUNUS. 



OSTEOPYGIS PLATYLOMUS, C\qc Sp. Nov. 



This species is represented by portions of two individuals, first perhaps half the carapace and plastron with all 

 the marginal hones of one side, and many of those of the other, of a large individual from the Peinberton Marl Com- 

 pany's Pits, Burlington Co., N. Jersey, presented to the Academy by Dr. Samuel Ashhurst; the second, a few por- 

 tions from the pits of David Haines, near Mcdford, Camden Co., N. J. 



The carapace is flat, as indicated by the slight curvature of numerous costal bones, and without keels, as indi- 

 cated by an anterior and two posterior vertebral bones. The posterior and adjacent margin is flat and wide, extend- 

 ing to a thin edge. The anterior vertebral, has the anterior margin entirely forming a deep notch, extending to 

 nearly opposite the lateral angles of the bone a feature not seen in the genus Chelone. It is crossed not far from 



its middle (it is broken behind) by the dermal suture, The posterior vertebral is transverse, occupies a concavity 

 forroed.by the three posterior marginals, extending to beyond the middle of the penultimates on each side. The 

 posterior vertebral dermal scute is of great width, its outer suture not reaching the marginals on any of the bones 



just mentioned. The anterior vertebral scuta, as seen on numerous COStal bones, were of peculiar form. Their 

 borders diverged very little, at their anterior and posterior portions, but curved outwards abruptly to meet the, costal 

 dermal suture, forming an acute angle. 



Marginal bones heavy at the sides and in front, the former concave on the upper face, the lower face plane but 

 upturned at the edge. Front laterals convex below with broad rounded margin; none of these projecting above the 

 marginal derma] suture; except to foim suture with costal plate as in C. repanda. This suture; lirst, appears on the 

 middle; of the tenth marginal bone counting the lateral caudal as iirsl, : marginal hones eleven on each side, all with 

 equal lengths, as in Chcloniidae. 



The rib pits are Hat, very much so medially, the anterior one more nearly cylindric. 



The width of the marginal scute on the ninth and' tenth marginal bones, is 1.66 its length, measuring from the 

 obtuse margin. The width of the first (posterior) scute is nearly equal to its length. 



The surface of the bone generally is marked by small irregular straight grooves. 



Portions of the sternum arc parts of two hypo, a hyo-, and xiphisternal. The lryposternal of the left side has a 



