158 



THE EXTINCT BATRACHIA, BEPTILIA 



costals is without gomphosis, and by light squamosal suture, except in front and at the 

 bridge, where the suture is closer and the bones thicker. 



In three species the iliac pit has been seen in numerous specimens from both sides of 

 the carapace. In all cases it is very elongate, opening posteriorly on the plane of the 

 costal bone. It extends to near the margins of the last and penultimate costals, commen- 

 cing near the proximal or vertebral end. The pit which receives the axillary buttress is 

 well defined, near the extremity of the first costal bone ; the end opposite to it is crossed 

 by a suture of the first vertebral scutum ; a ridge also extends from the pit to the capitu- 

 lum: just anterior to the latter a strong crest probably represents the connate first rib, 

 which is free in some Emydidffi. 



The posterior lobe of the plastron is deeply emarginate. 



The materials on which the generic and specific characters of the tortoises included 

 undei this head have been based are abundant in the middle bed of Cretaceous Green 

 Sand in New Jersey, but are usually obtained in such a fragmentary condition as to require 

 much labor for their interpretation. The case; has been especially difficult in the present 

 genus, owing to the difference in the sculpture of different parts of the; same carapace. 

 These varieties are the longitudinal parallel grooved surface, the coarser and more finely 

 reticularly grooved, and the plane ; the last either erosc or smooth. The reticulate groove 

 is sometimes so deep, and the areola; so raised as to be truly tubercular. 



These differences indicate both parts of the same species and different species. The 

 longitudinal grooving is characteristic of the costal hones of Taphrosphys strcnuus, and 

 the costal and some thoracic bones of T. molops. The reticulate sculpture is close on the 

 marginal bones of T. molops and T. sulcatus, closest on a portion of the bridge; of the; for- 

 mer. It is coarse and open on the abdominal bones of T. molops and T. sulcatus, but 

 often passes into an eroded surface, which gives no distinct pattern, but is generally 

 roughened. In P. nodosus the reticulate sculpture is so close and strong, as to leave tu- 

 bercle-like interspaces; while P. enodis is entirely smooth 



Six species may be clearly distinguished. They differ considerably in the forms of the 

 mesosterna] bones, and their relations to the intergular scutum, which covers them in 

 part. The forms of the pubic and inguinal sutural articulations are also quite character- 

 istic, as well as the relative thickness of the shells. In size the species vary from that of 

 an average snapping turtle ('I. lcslianus) to that of the largest sea turtles (T. strcnuus.) 



Synopsis of Species, 

 a An azygus bone in front of the caudal marginal. Taphrosphys, 

 Mesosternum transverse, broader than long; intergular scute, not reaching the; poste- 

 rior border ; first vertebral scute shorter ; shell heavy; pubic scar wide, much elevated; 

 xiphisternum thin edged ; large size. T. MOLOPS. 



