[Cope. ^^^ [March 4, 1870. 



front. The suture between the hypo- and xiphisternals is nearly transverse 

 below ; on the upper face it sends a process into the hyposternals for- 

 wards, which is acuminate ; the hyposternals send a marginal process 

 backwards beyond the line of the median suture, Avhich is squarely trun- 

 cate ; its outer edge is the margin of the bone. The impressions of con- 

 ta.ct of the pubes are well marked ; they are strongly incurved, and are 

 not very different from those seen in Cistudo. The bridge of the plas- 

 tron is preserved, and furnishes attachment for three marginal bones ; per- 

 haps fractions of others also. The suture between the abdominal and 

 humeral scuta is convex backwards, and unites with an inner angle of the 

 anterior of the intermarginal series of the bridge. There are three in the 

 latter series, all longer than broad, but the middle one relatively much 

 narrower than the others, as it is six times longer than wide, with paral- 

 lel sides. That anterior to it is more hexagonal and wider, presenting an 

 angle inwards for union with the suture between the abdominal and 

 humeral scuta. 



About half the mesosternal bone is preserved. It is a transverse dia- 

 mond with truncate extremities. Its posterior angle is therefore very 

 open, but is not rounded. No suture bounding either humeral or gular 

 scuta is visible on it ; the anterior angle is broken away. The anterior 

 portion of the episternal bone preserved has a regular convex outline, and 

 is quite thin. 



The sculpture of the inferior surface is a slight imitation of that seen 

 in some species of Trionyx. It is closely shallow-punctate, or like small 

 rain-drop impressions. These are iri^egularly distributed on the anterior 

 part of the plastron, and on the posterior lobe in obliquely decussating- 

 series. 



Measurements. 



M. M. 



Width of plastron at bridge, . . , 0.2879 



Length between mesosternum and xiphisternum, 0.21 



Width posterior lobe at inguinal notch, . . 0.1835 



" mesosternum, . . . .0.091 



Length " .... 0.0695 



" hyosternum medially, . . .0.09 



Thickness " " . . . 0.012 



" " at marginal suture, . . 0.007 



Length abdominal suture, . . . 0.1063 



" femoral " . , .0.087 



Length median intermarginal suture, . . 0.0825 



Width " " " . , 0.015 



Estimated length plastron, . . . 0.45 



" " carapace, . . . .0.56 



This species, the largest of the genus, is found in the upper green sand 

 bed of the upper Cretaceous of New Jersey. The specimen from which 

 the above description was taken, was found by my friend I. C. Voorhees, 

 in the pits of the New Jersey Marl Company, and by the permission of 

 the latter submitted to the writer. 



