162 FOSSIL TURTLES OF NORTH AMERICA. 



Dr. W. B. Clark has referred provisionally (Johns Hopkins Univ. Circ., xv, 1895, No. 4; 

 Bull. U. S. Geol. Surv., 141, p. 59) some fragments of a large turtle to Euclastes. One of these 

 fragments has been again mentioned and figured by Dr. Case in the Eocene volume of the 

 Geological Survey of Maryland (p. 97, plate x, fig. 7). The fragment is not susceptible of 



generic determination. 



Rhetechelys platyops (Cope). 



Plate 29, figs, z, 3. 



Euclastes platyops, COPE, Proc. Acad. Nat. Sci. Phila. 1867, p. 41; Cook's Geol. New Jersey, 1868 

 (1869), p. 735; Amer. Naturalist, in, 1869, p. 89; Ext. Batrach., Reptilia, Aves N. A., 1869, p. 

 149, plates vi, vii, fig. 9; Vert. Cret. Form. West, 1875, p. 259. 



Lytoloma platyops, HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 442. WIELAND, Amer. Jour. Sci. 

 (4), xvin, 1904, p. 185. 



?Propleura sopita, COPE, Ext. Batrach., Reptilia, Aves N. A., 1869, p. 140 (Harrisonville specimen). 



All that we know at present regarding this species is what is to be derived from the type 

 skull. This is in the collection of the Academy of Natural Sciences at Philadelphia. It was 

 found in a coarse granular limestone, at HurfFsville, Camden County, New Jersey. This 

 deposit belongs to the Upper Cretaceous and was regarded by Cope as equivalent to the Fox 

 Hills group. The species formed the type of Cope's genus Euclastes, a preoccupied name. 



The skull was a large one, the total length being estimated by Cope as u inches, about 

 280 mm.; but this must have included the supraoccipital process. At any rate, the length was 

 equal to that of the largest specimens of Caretta. The occipital condyle is missing, but the 

 length from the premaxillae to this condyle must have been close to 200 mm., perhaps a little 

 more. The width, a short distance behind the orbits, is 220 mm. From this widest part the 

 aiteral outlines converge rapidly to the pointed snout. Beneath the orbit the outlines are 

 slightly concave. The angle included between the borders of the maxillae is somewhat less 

 than a right angle. The roof is broad and deprest, the frontal region being flat. The slope 

 from the rear to the nasal opening is only slightly sinuous. There is no such sudden descent 

 from the orbits to the premaxillae as we see in the species ofGlossochelys. The temporal region 

 was broadly rooft over, as in Caretta, but extended backward still further. The various bones 

 appear to have been disposed about as in the living genus mentioned. 



The orbits look outward, forward, and upward. The upward inclination exceeds that of 

 Caretta. The greatest diameter of the orbit is 63 mm. The least interorbital width is about 

 50 mm. The frontal bones are more produced forward than in Caretta, their suture measuring 

 55 mm. They are excluded from the rim of the orbits by the union of the postfrontals with the 

 prefrontals. The latter bones meet along the midline a distance of 12 mm. 



The nasal opening has a width of 30 mm. It looks forward and strongly upward. As in 

 other Cryptodira, the prefrontals send downward on each side a column of bone to the vomer. 



The roof of the mouth resembles in general that of Caretta, but there are important differ- 

 ences. The cutting-edges of the maxillae are only feebly developt, descending but little below 

 the level of the grinding surface. This surface is formed by the union of the palatal plates of 

 the premaxillae, maxillae, vomer, and palatines. It extends backward a distance of nearly 

 100 mm. from the premaxillae. It is somewhat concave on each side of the vomer and in the 

 premaxillary region. In the roof of the mouth the maxillae are each 41 mm. wide; the palatines 

 about 26 mm. The vomer is 50 mm. long and 28 mm. wide. 



The occipital condyle is missing, but the choanae fall within the anterior half of the length 

 to the roof of the mouth. They are bounded laterally by the palatines and anteriorly by the 

 vomer, the edge of this being 98 mm. behind the tip of the snout. They are thus quite different 

 from those of the species of Erquehnnesta. The palatal openings of the temporal fossae are 

 broader than long. The borders of the pterygoids were strongly emarginated. 



Between the anterior ends of the premaxillae is a perforation supposed to be for the recep- 

 tion of a hook on the lower jaw, as in Macrochelys. 



Professor Cope supposed that the whole length of the animal which possest this skull 

 was a little over 6J feet; but it is not safe to estimate the size of a turtle from the size of the 

 head. Nevertheless, it must have been a large and formidable brute. Probably it haunted 

 the coasts of the Cretaceous seas, betaking itself at times to some distance from the shore. 



