169 



tionately of more robust character than in Emys. The ilium in shape is 

 more like that of this genus than that of the snapper, but is proportionately 

 of 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 acetabulum and commencements of the ischiatic and pubic rami prc : 

 sent nothing peculiar from the condition observed in the snapper. 



Measurements of the pelvic specimens are as follows : 



Lines. 



Length of sacrum beneath, the centra Oj 



Length of first sacral centrum '. 4J 



Breadth of first sacral centrum ±\ 



Length of second sacral centrum 4£ 



Breadth of second sacral centrum 4f 



Breadth of sacrum at first pair of alse 30 



Length of first sacral alae 13 



Length of second sacral alse ■. 11 



Length of innominatum 23 



Breadth of crest of innominatum IS 



Height of acetabulum G 



Breadth of acetabulum di 



CHISTERNON. 



Chisteenon undatum. 



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

 miles from Fort Bridger, 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 which 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 much 

 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 the great 

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

 22 o 



