266 0. P. Hay — Fossil Turtles in the Marsh Collection. 



>mm 



width at the upper border of the tympanic cavity is 58 r 

 There is no roof over the temporal region, and there is no 

 parieto-squamosal arch. The postorbital arch is but little more 

 than 7 mm wide. The zygomatic bar is excavated on its lower 

 border. The interorbital space, as shown by the American 

 Museum specimen, is 23 mm wide. The orbits are large, having 

 an antero-posterior diameter of about 20 ram . The nares, as 

 shown by the specimen last mentioned, have a perpendicular 

 diameter of 16 nim . The upper jaw is convex along its cutting 

 edge, rising in front so as to form a median notch. This edge 

 is sharp throughout its length. In the Yale specimen, the 

 lower jaw conceals a portion of the palate near the cutting 

 edge, but this region is exhibited in the American Museum 

 specimen. Running parallel with the posterior half of the 

 cutting edge, and separated from it by a deep furrow, is a 

 sharp dentated ridge, which has a length of 12 mm . When the 

 jaws are closed this ridge fits into a groove in the lower jaw. 



The choanse are far forward. The roof of the mouth is 

 vaulted, not greatly unlike that of Testudo. The vomer 

 appears to have extended backward nearly to the pterygoids. 

 The distance across the palatines at their posterior ends is 20 mm . 

 The distance across the constricted portion of the pterygoids is 

 13 mm . There are small postpalatine foramina. The outer 

 border of the palatine bone has not been traced with certainty. 

 In the specimen in the American Museum there appears to be 

 a suture running along the bottom of the groove on the out- 

 side of the dentated ridge mentioned above. If this is really 

 the case, this ridge lies on the palatine bone. 



The tympanic cavity has its posterior wall open, forming a 

 channel for the passage of the stapedial rod. The sutures 

 between the bones of the skull are closed, and some of them 

 can be traced only with difficulty. There appear to have been 

 no nasals. As shown by the American Museum specimen, the 

 frontals are shut out from the borders of the orbits. 



The lower jaw appears to have formed a slight beak in front. 

 The anterior half of the efficient border forms a cutting edge 

 which shears against that of the maxilla. Posteriorly the edge 

 divides so as to produce two ridges which enclose between 

 them a deep groove about 4 ,nm wide. It is this groove which 

 receives the dentated ridge of the palate. 



Portions of the hyoid apparatus remain clinging to the base 

 of the skull. This apparatus resembles closely the same organ 

 in Chrysemys elegans, and is much unlike that of Dermatemys. 



Text-figure 2 shows the form of the plastron, and this agrees 

 with that of the specimen in the American Museum. Leidy 

 (Contr. Ext. Fauna West. Terrs., pi. xv, fig. 6) has figured the 

 anterior end of a plastron which is truncated and slightly exca- 



