DESMATOCHELYIDiE. 187 



The lower jaw is firmly cemented to the skull, hence no examination can be made of the 

 triturating surfaces; they were, however, undoubtedly narrow. The symphysis is 43 mm. long. 



Y\ ilhston has described and figured one cervical vertebra. It is 26 mm. long, a fact indi- 

 cating that the neck was short. The articular surface is 26 mm. from side to side and 15 mm. 

 vertically. Near the hinder end of the centrum there is, on each side, a stout transverse process. 



The sacral and several caudal vertebras are preserved and have been described by Williston. 

 1 he caudals are all small and proccelous. 



The length of the scapula, measured from the tip to the lower border of the proscapular 

 process, is 158 mm. The process just named is 82 mm. long. The coracoid has a length of 

 100 mm. and a width, at the free end, of 35 mm. The shaft is much constricted in the middle 

 of the length. 



The humerus (fig. 240) is a large flat bone, which, by its whole structure, shows that it 

 belonged to a turtle which dared the open seas. The length, from the proximal surface of the 

 head to the distal end, is 202 mm.; while the extreme length is 260 mm. The last dimension 

 indicates the great height of the ulnar process. The width across the head and the ulnar 

 process is about no mm. The shaft, where narrowest, has a diameter of 80 mm. The distal 

 end is rounded and has a width of 80 mm. The radial process is large and extends downward 

 on the shaft about 90 mm. below the upper surface of the head. 



Williston figures a radius, a supposed ulna, and various bones belonging to the hand. 

 Fig. 241, from Williston, represents the ilium, ischium, and pubis of the right side. Williston 

 figures also an incomplete femur. Evidently it was a feebler bone than the humerus. 



But little of the carapace was secured. The costal plates have a thickness of only 2 or 3 mm. 

 The rib-heads are stout. One of the hinder costals has a width, near the proximal end, of 

 40 mm. The neural corresponding to it is 32 mm. wide. No sulci have been observed on any 

 of the bones of the carapace. 



Fig. 242, from Williston, represents the pygal and the adjoining right peripheral. The 

 pygal measures antero-posteriorly at the midline, 61 mm.; and from side to side, 97 mm. 

 Its thickness is 6 mm. 



Fig. 243 represents a fragment of one of the plastral bones and one of the lateral peripherals. 

 Evidently, the plastral bones were loosely connected with the carapace, as in the Cheloniidae. 

 The peripheral has a length of 130 mm., and a width of about 35 mm., and a thickness of 6 mm. 

 Other peripherals, believed to be more anterior in position, are thicker and longer. 



Not enough of the plastron was secured to furnish exact knowledge regarding its structure. 



Genus NEPTUNOCHELYS Wieland. 



A genus based wholly on a humerus of a turtle which was adapted for life on the sea. 

 Humerus flattened; the head, the ulnar, and the radial processes in the plane of flattening, or 

 nearly so. Radial process not so far removed from the head as in the Protostegidae. Humerus 

 resembling that of the Cheloniidae, still more that of Desmatochelys, differing from the latter 

 in having the head more nearly in the axis of the bone and the ulnar process nearly parallel 

 with the axis. 



Type: Neptunochelys tuberosa (Cope). 



Neptunochelys tuberosa (Cope). 

 Fig. 244. 



r'Holcodus at utidens, Leidy, Smithson. Contrib. Knowl., Xiv, art. vi, 1865, pp. 42, 1 18, plate viii, figs. 1,2. 

 Protostega tuberosa, Cope, Fifth Ann. Report U.S. Geol. Surv., Montana, etc., 1871 (1872), p. 334; Vert. 



Cret. Form. West, 1875, p. 257. 

 Atlantoehelys tuberosus, Leidy, Ext. Vert. Fauna West. Terrs., 1872, p. 342. 

 Neptunochelys tuberosa, WlELAND, Amor. Jour. Sci. (4), ix, 1900, pp. 417, 418. Hay, Bibliog. and 



Cat. Foss. Vert. N. A., H)02, p. 440. 



No part of this great sea-turtle is known except the humerus. This was found many 

 years ago by Dr. Spillman, in Upper Cretaceous deposits, at Columbus, Mississippi. Having 

 been found associated with the bones of a mosasauroid reptile and described before the limbs of 

 the lYIosasauria were known, it was believed to be possibly the humerus of Holcodus acutidens. 



