104 FOSSIL TURTLES OF NORTH AMERICA. 



ally, the pterygoids are wide, and the outer border is uprolled in a scroll-like manner. The 

 basisphenoid, most of which is present, is large, the width being 13 mm. 



The most striking feature of the skull is presented by the triturating surfaces of the upper 

 jaws. On the premaxillae they are very narrow. Backward each expands rapidly and occupies 

 most of both the maxilla and the palatine. The greatest width is 24 mm. Each, instead of 

 being flat, is deeply excavated. At the suture between the maxilla and the palatine the exca- 

 vation contracts into a circular pit which rises in the maxilla to the height of the floor of the 

 orbit. The walls inclosing this pit are smooth. The remainder of the triturating surface is 

 perforated by openings for blood-vessels. 



The lower jaw shows little else than the co-ossified dentaries. These are of very solid 

 construction. The jaw as a whole is thin and pointed in front, but the coronoid processes rise 

 to a height of 27 mm. The symphysis has a length of 20 mm. The triturating surfaces are as 

 remarkable as those of the upper jaw. Each may be described as containing a deep pit, 

 situated at the hinder end of the dentary and opening forward and upward, trumpet-like, on 

 the upper surface ot the dentary. The trumpet-shaped mouth extends forward to near the tip 

 of the jaw. It is bounded outwardly by the cutting-edge of the jaw; inwardly by a ridge, which 

 rising at the tip of the jaw, runs backward and upward, increasing in height to the coronoid 

 process, along the inner border of the ramus. 



The purpose ot the pit-like excavations in the jaws, upper and lower, is problematical. 

 In speaking of the pit in the upper jaw Leidy said that it did not appear like an alveolus for a 

 tooth, but that it may have accommodated a corneous tooth-like process springing from the 

 corresponding hollow of the lower jaw. Baur thought that the pits lookt much like the alveoli 

 of large tusk-like teeth. 



It does not appear probable that there were any teeth in this turtle. It seems far more 

 probable that both jaws were covered with plates of horn, as are those of all other known 

 turtles. The whole construction of the skull of Bothremys indicates that it was accustomed to 

 crush hard objects as food. Probably these objects were of such a nature that economy of 

 force demanded that they should be brought to a particular spot on the jaw for crushing. To 

 provide for the rapid reproduction of the horn beneath these areas for crushing, these pits 

 became developt in a way analogous to the human "nail-bed." 



Genus TAPHROSPHYS Cope. 

 Prochonias Cope. 



A genus of pleurodirid turtles known only from the shell. Carapace with 7 neurals, the 

 costals of the seventh and eighth pairs meeting their fellows at the midline; a large suprapygal; 

 and 11 pairs of peripherals, the posterior thin and with acute free borders. No nuchal scute. 

 Plastron with 1 1 bones, the mesoplastrals small and well out on the bridges. A single intergular 

 almost wholly confined to the entoplastron. Hinder lobe with large notch. Large pits in the 

 first and the fifth costals for the axillary and inguinal buttresses. Ilium firmly articulated with 

 the carapace at the junction of the seventh and eighth costals. Ischium and pubis articulated 

 to the xiphiplastron. 



Type: Platemys sulcatus Leidy. 



In Cook's Geology of New Jersey, 1868 (1869), page 735, Cope mentions the generic name 

 Taphrosphys in connection with 3 specific names, as follows: T. molops, T. princeps, and 

 T . sulcatus. The first two had not yet been described, the last was Leidy's Platemys sulcatus. 

 In the April (1869) number of the American Naturalist, Cope again mentions the name 

 Taphrosphys, this time in connection with molops only, while to the new genus, Prochonias, 

 were referred the species P. sulcatus, P. strenuus, and P. princeps. Of these again none had 

 yet been described except P. sulcatus (Leidy). The latter therefore is the type both of 

 Taphrosphys and Prochonias. Which of these names has precedence depends on which was 

 issued first to the public, the April number of the American Naturalist or Cook's Geology of 

 New Jersey. Investigations not wholly satisfactory seem to show that the latter was first 

 publisht, probably some time about the first of March, 1869. This conclusion enables us to 



