0. P. Hay — Fossil Turtles in the Marsh Collection. 265 



regarded as distinctive, since there are Cryptodira (Porthochelys) 

 which possess nasals. A short supraoccipital spine is very 

 general among the Pleurodira. The character which especially 

 separates the latter group from the Cryptodira is found in the 

 very broad pterygoids, the posterior ends of which do not 

 separate the quadrates from the basioccipitals. In Baena, as 

 shown in the present skull and in others from the Bridger beds 

 not yet described, the pterygoids are disposed in the same way 

 as in the Cryptodira. 



It appears, in fact, that a considerable number of characters 

 exist in the skulls of Baena, which belong also to the Athecse. 

 These are found in the short supraoccipital spine, the large 

 postfrontals, the exclusion of the frontals from the orbits, and 

 the participation of the basioccipital in the formation of the 

 foramen magnum. 



The nasals, the lachrymals, and the extensive temporal roof 

 may be regarded as primitive characters. 



In Baena, undoubted pleurodiran characters are seen in the 

 presence of a mesoplastron and in the structure of the cervical 

 vertebrse. The suborder Amphichelydia must thus be regarded 

 as securely founded. 



Baptemys wyomingensis Leidy. 



Plate XIII, Figures 1-3 ; Text-figure 2. 



Baptemys tvyomingensis, Leidy, J., Proc. Acad. Nat." Sci. Pliila., 1870, p. 5; 

 Contr. Ext. Fauna West. Terrs., 1873, p. 157, pi. xii, pi. xv, fig. 6. 



This species is represented in the Marsh collection by a 

 specimen which was collected in the year 1870, in the Bridger 

 beds, near Millersville, Wyoming. The carapace is almost 

 entire, but somewhat crushed and distorted. The plastron is 

 intact. The nearly complete skull is present ; likewise, some 

 of the limb bones. The specimen bears the number 484. It 

 is most valuable on account of furnishing the hitherto unknown 

 skull and the not well-known anterior lobe of the plastron. 



When this example is compared with the type some differ- 

 ences are observed, but these are not regarded as of specific 

 value. The most important of these differences is the presence 

 of four, instead of three, inframarginal scutes on each of the 

 bridges. 



The only portion missing from the skull is the roof of the 

 orbits and the nasal cavity. This deficiency is fortunately sup- 

 plied by a skull collected during the year 1903 by the Ameri- 

 can Museum expedition into the Bridger bed's near Fort 

 Bridger. 



The skull is wedge-shaped, being broad behind and pointed 

 in front. The length from the snout to the occipital condyle 

 is 67 mm ; to the end of the supraoccipital spine, 88 m,n . The 



