198 



FOSSIL TURTLES OF NORTH AMERICA. 



As regards its habits, we may safely conclude that this turtle was an active swimmer on the 

 open seas and that it was carnivorous in its diet. Wieland is of the opinion that all the members 

 of this group were powerfully equipt for both swimming and attack, and may well have 

 hunted actively swimming prey. As to swimming, we must remember that the boldest swimmer 

 among turtles of our day is the leatherback, which has an elongated body. The short, broad 

 carapace of Protostega must have imparted to the animal an unsteady bearing under efforts to 

 make rapid progress. 



As regards the nature of the food, the long symphysis of the lower jaw appears to indicate 

 a habit of crushing hard-shelled animals, such as crustaceans and mollusks. 



Protostega potens sp. nov. 



Figs. 246, 254, 255. 



This species has as its type No. 180 of the American Museum of Natural History. This 

 was collected by Mr. H. T. Martin, in 1897, in the Niobrara beds, near Elkader, Logan 

 County, Kansas. The individual is represented by large portions of the skeleton, but only a 

 part of it has been prepared for study. 



There is present the hinder half of the left side of the skull. This is strongly crusht down- 

 ward and toward the right side. The structure appears to be in general the same as in P. 



FIGS. 254 AND 255. Protostega potens. Basioccipital and hyoplastron of type. 



254. Section across front of basioccipital. X ! 



255. Hyoplastron. Xj. 



gigas. Sutures are not discernible, but from the striations on the bones, their limits may be 

 pretty accurately determined. The orbit had a perpendicular diameter of 70 mm. The dis- 

 tance from the hinder border of the orbit to the posterior angle of the squamosal was nearly 

 200 mm. On lifting the anterior end of the parietal there is exposed a broad plate of bone 

 which runs downward from the inner border of the parietal. This is without doubt the descend- 

 ing plate of the parietal, whose presence has hitherto been somewhat doubtful. The occipital 

 condyle is large, having a diameter of 50 mm. The bones composing it are wholly co-ossified. 

 Its inferior portion is eroded away. The condyle is broadly rounded behind, without trace 

 either of a pit or of division into its constituent three bones. The lower surface of the basi- 

 occipital appears to have been greatly different from that of P. gigas. Case describes the latter 

 as having its under surface nearly smooth and lying in the plane of the horizontal axis of the 

 skull. From this we may infer that this surface is nearly flat. In the present species the midline 



