CHELONIIDAE. 



213 



obtuse, and along the hinder third is somewhat dentated. Anteriorly, the upper surface is 

 furnisht with ridges which are sharp and prominent as they approach the free inner border, 

 but which become obsolete in the opposite direction. These ridges seem to diverge from the 



anterior buttress of the hyoplastron (fig. 270, C), if such 

 existed. At the anterior end of the bone the inner border 

 turns slightly outward and, at an angle of about 75 , meets 

 the sutural border for articulation with the epiplastron (fig. 

 270, A to B). These bones were not joined by squamosal 

 suture, as they are in the Cheloniidae and the Chelydridae, 

 but by dentated suture. The lower surface of the bone is 

 smooth and convex, especially transversely. The upper 

 surface is concave. At the anterior end of the bone, on 

 the upper surface, 190 mm. behind the anterior end (fig. 

 270, C), is a slight elevation, as if it were the base of an 

 axillary buttress. The lower surface of the bone just behind 

 this point also indicates that the plastron rose toward the 

 carapace. 



The portion of hypoplastron has a length of 155 mm. 

 and a width of 125 mm. Anteriorly the suture for the hyo- 

 plastron is missing. The inner border is subacute and 

 smooth, thus differing from the corresponding border of the 

 hyoplastron. The suture for the xiphiplastron runs at right 

 angles with the midline. It shows that the two bones were 

 firmly united by coarse interdigitating teeth. Toward the 

 outer border the bone has a thickness of about 13 mm., 

 but this diminishes slowly toward the inner border. As the 

 outer border is approacht, the bone begins to ascend in a 

 decided manner, as if approaching the carapace (fig. 270, 

 D). If this conclusion is correct, as indicated by both Inn- 

 plastron and hypoplastron, these bones were, relatively to 

 their length, very narrow; and there is indicated a wide fonta- 

 nel, that extended from the entoplastron to the xiphiplastra. 

 It seems improbable that the inner borders came into close 

 proximity. There were certainly no digitations extending 

 from the hyoplastron and hypoplastron toward the mid- 

 line, as there are in the Cheloniidae and the Chelydridae. 

 A fragment of bone present indicates that the hyohypo- 

 plastral suture was formed by the interdigitation of finer 

 processes than that of the hypoxiphiplastral suture. On the anterior end of the fragment of 

 hypoplastron there are traces of this suture, so that this bone appears to have had a fore- 

 and-aft extent of about 170 mm. 



The fragment of scapula present was that of a very large turtle. It is possible that it did 

 not belong to the same individual as the plastral bones. The long diameter of the neck of 

 the bone is 98 mm.; the short diameter, 42 mm. 



In.. 270. Lembonax polemicus. 

 Portion of plastron. Type. X}. 

 No. 1 134 A.M.N. H. ' 



A to B, border for articulation with the epi- 

 plastron ; C, base of axillary buttress ; 

 1), probable base of inguinal buttress; 

 hyo, hyoplastron; hypo, hypoplastron. 



Lembonax? insularis Cope. 

 Fig. 271. 



Lembonax insularis, Cope, l'roc. Acad. Nat. Sci. Phila. 1872, p. 16. Hay, Bibliog. and Cat. Foss. 

 Vert. N. A., 1902, p. 44+. 



Professor Cope's materials representing this species were meager and his descriptions of 

 it unsatisfactory. Nor have the means for increasing our knowledge of it been augmented; 

 the) have even been reduced. In the American Museum of Natural History there is a lot of 

 bones labeled by Cope as the type of his Lembonax insularis, and bearing the museum's 

 number 2347. This lot came to Cope from the Eocene bed of greensand at Vincentown, 

 Burlington County, New Jersey. Cope stated that the species was based on nuchal and 



