102 FOSSIL TURTLES OF NORTH AMERICA. 



The surface of the bone is covered with rounded elevations which resemble small bird shot. 

 There are about eight in a line 10 mm. long. The basis of each elevation is often of less 

 diameter than the body of it. Many of them are broken off near the surface of the bone, 

 leaving circular scars. Along the edges of the bone which joined the hyoplastra there is a 

 narrow border nearly free from the pustules. 



This turtle differed from Polythorax missuriensis in the character of the ornamentation, 

 this consisting in the latter species of short raised lines. In that species, too, the pectoro- 

 humeral sulcus appears to have been pushed well forward. In the species here described 

 there is no trace of the presence of this scute. 



Superfamily PLEURODIRA Cope. 



Thecophorous turtles having a carapace composed of costals and peripheral bones and 

 usually a series of neurals and a plastron in which the epiplastra are in contact with the hyo- 

 plastra. Mesoplastra present or absent. Intergular scutes developt, the inframarginals 

 wanting. Temporal roof of the skull varying from nearly complete to nearly obsolete. Ptery- 

 goids not extending backward between the quadrates and the basisphenoid; broad, with the 

 outer border uprolled. Neck bending sideways; not capable of being withdrawn between the 

 scapulae. Ilia suturally joined to the eighth costals; the pubes and the ischia, to the xiphi- 

 plastra. 



The living Pleurodira are divided by Boulenger into 2 families, the Pelomedusidae and the 

 Chelydidae. About 30 species are known. None of these have had the anterior limbs trans- 

 formed into flippers, like those of the Cheloniidas. The geographical distribution of the living 

 species is illustrated by fig. 15, on page 34. The earliest turtles certainly known to belong to 

 this superfamily occur in the Upper Cretaceous of North America. Cope referred these to the 

 Pelomedusidae; but the present writer, following Baur, accepts for them the family Bothremy- 

 didae. So far as is known, no species of the superfamily lived in North America after the end 

 of the Upper Cretaceous. 



Family BOTHREMYDIDjE Baur. 



Extinct pleurodire turtles having the skull probably extensively rooft over in the temporal 

 region. Vomer present. Triturating surfaces of the jaws, upper and lower, broad and deeply 

 excavated. Shell as in the Pelomedusidae, with small mesoplastra. 



Baur was the author who proposed this family, making it include Bothremys and Taphro- 

 sphys. Cope had arranged these genera under the Podocnemididae. To the present writer 

 it appears that the presence of a vomer, but still more the extraordinary excavations found 

 in the jaws, upper and lower, are sufficient to set off Botlimnys as a member of a distinct family. 

 With it must go for the present Tapkrosphys. 



Key to the Genera. 

 A. Known from skull only: 



Each side of jaws, upper and lower, with a deep pit Bothremys 



A A. Known from shell only: 



1. Nuchal bone not shortened; free borders of peripherals acute Taphrosphys 



2. Nuchal short and broad; free borders of peripheral obtuse Amblypcxa 



3. Only the xiphiplastron known; the ischiadic scar extending to the midline Naiadochelys 



Genus BOTHREMYS Leidy. 



Vomer well developt, not separating the palatines. Choanae behind the centers of the 

 orbits. The nasal passages underfloored by the surrounding bones. Crushing surfaces of jaws 

 broad and occupying portions of the maxilla; and of the palatines; the excavation contracting 

 to a pit in each. Lower jaw with the dentaries co-ossified. Shell unknown. 



Type: Bothremys cooki Leidy. 



It has been suspected that the skull represented by the type of Bothremys is that of some 

 species of Taphrosphys, all the species of which are known only from shells. This is entirely 

 possible, but nothing is to be gained at present by reducing Taphrosphys to a synonym of 

 Bothremys. 



