169 



tionately of more robust cliaracter than in Erays. The ilium in filunx! is 

 more like that of this genus than that ot the snapper, l)ut is proportionately 

 ol' much greater breadth, the wing being of nearly double the expanse. 



The expanded extremity of the first sacral wing articulates with the ante- 

 rior extremity of the crest of the ilium. In Emys it articulates with the 

 latter midway to the two prominent extremities of the crest. 



The acetabuhim and commencements of the ischiatic and pubic rami pi-e- 

 sent nothing peculiar from the condition observed in the snapper. 



Measurements of the pelvic specimens are as follows : 



Lines. 



Length of sacrum beneatli the centra 9j 



Length of first sacral centrum 4^ 



Breadth of first sacral centrum .■ 4.J 



Length of second sacral centrum 4^ 



Breadth of second sacral centrum 4? 



Breadth of sacrum at first pair of alae 30 



Length of first saci'al alae , 13 



Length of second sacral alaj 11 



Length of innominatum 23 



Breadth of crest of innominatum 18 



Height of acetabulum C 



Breadth of acetabulum 9J 



CHISTERNON. 



Chisternon undatum. 



A large turtle-shell, discovered by Dr. Carter in a chain of buttcs a few 

 miles from Fort Bridgcr, and presented to the Academy of Natural Sciences 

 of Philadelphia, was originally described by me under the name of Baena 

 undata. A careful examination of the specimen has led me to view it as per- 

 taining to a different and heretofore undescribed genus. 



The specimen represented in Plate XIV, one-half of the diameter of nature, 

 consists of the intermediate portion of a shell, with the extremities broken 

 away nearly in the position of the broad columns wliich spring from the plas- 

 tron to support the carapace. Though much fractured, it appears to have 

 been but little so while it lay imbedded in the deposit from which it was 

 derived, so that it now retains its orginal form. The upper shell is as mucli 

 vaulted as in some of the living land-turtles. This form, together with the 

 thick bone and strong, broad sternal supports, enabled it to sustain tlic grt'ut 

 weight of superincumbent pressure which has crushed so many of its asso- 

 22 G 



