212 



FOSSIL TURTLES OF NORTH AMERICA. 



The humerus (fig. 269) resembles that of a true sea-turtle. The total length is loomm. The 

 distal end is broad and flat. The head of the bone is elongated reniform, the long axis being 

 at nearly right angles with the plane of the distal end. Its long diameter is 32 mm.; the 



shorter, 17 mm. The ulnar process is broken away, 

 but a groove separated it distinctly from the head. 

 The radial process is divided into two portions; one 

 part being on the under side of the shaft, 40 mm. 

 below the upper border of the head; the other part 

 on the radial border, still further down on the shaft. 

 Both portions are prominent. The narrowest part 

 of the shaft is 20 mm. wide and II mm. thick. The 

 distal end is 41 mm. wide. The ectepicondylar pas- 

 sage is a foramen. It emerges on the lower side 

 of the bone 10 mm. above the distal extremity. 

 The condyles are distinctly separated from the sur- 

 rounding bone. Their fore-and-aft extent is 22 mm. 

 The radial epicondyle is broad, thick, and flat; the 

 ulnar little prominent. It is remarkable that Cope 

 in his description of this bone regarded the anterior 

 border as the posterior. 



Genus LEMBONAX Cope. 



FIG. 2 6g.~Syllom U s cnspatus. Right Plastron with probably a fontanel extending 



humerus Type X. from the entoplastron to the xiphiplastra. No 



dictations of bone proceeding from the plastral 



On left, the ventral surface; on right, the radial border. & . r. . o 



bones toward the midhne. tpiplastra firmly sutured 



to the hyoplastra, the suture oblique to the midline; the xiphiplastra similarly joined to the 

 hypoplastra, the suture at right angles with the midline. 

 Type: Lembonax polemicus Cope. 



The position of this genus is very problematical. Cope concluded originally that the 

 relationships were with the Chelydridae rather than with the Cheloniidae. At a later time he 

 stated (Amer. Naturalist, xvi, 1882, p. 989) that not enough was yet known to assure us to 

 what family the genus belonged, except that they were not Trionychidae. Nothing has been 

 added to our knowledge on that point since that time. Cope referred two additional species, 

 L. propylceus and L. insularis, to the genus. While the present writer retains these species 

 in this genus provisionally, there appears to be no evidence whatever that they belong there. 



For want of knowledge where Lembonax polemicus belongs it is here referred to the 

 Cheloniidae. 



Lembonax polemicus Cope. 



Fig. 270. 



Lembonax polemicus, COPE, Ext. Batrach., Reptilia, Aves N. A., 1870, p. 168. HAY, Bibliog. and 

 Cat. Foss. Vert. N. A., 1902, p. 444. 



This species was sent to Professor Cope from the Eocene greensand near Farmingdale, 

 Monmouth County, New Jersey. The type and only known specimen is now in the American 

 Museum of Natural History and bears the number 1134. It furnishes a portion of the plastron 

 and the base of the scapula. The materials indicate a large individual, but they furnish 

 meager information regarding its structure and relationships. 



The most important parts of the plastron are a portion of the right hyoplastron and a 

 portion of the right hypoplastron. The outer borders of both these bones are wanting. 



The hyoplastral fragment (fig. 270) has at present a length of 233 mm., having apparently 

 lost a slight portion since it was studied by Cope. The greatest width is 136 mm. The thick- 

 ness varies from 10 to 15 mm. Anteriorly the bone terminates at the union with the epi- 

 plastron. Posteriorly, there is no indication of suture with the hypoplastron, and this may 

 have been farther away than indicated in the figure. The inner border of the bone is thick, 



