164 FOSSIL TURTLES OF NORTH AMERICA. 



The known species of this genus, 7 in number, are from the Niobrara deposits of Kansas. 

 All these species except T. bauri Wieland are based on parts of the skull; and this portion 

 of the skeleton is more commonly found than even the carapace, a rare circumstance in the 

 case of fossil turtles. However, the greater part of the shell and limbs is known from two or 

 three of the species. 



From studies made on this genus some years ago (Field Columb. Mus. Pubs., Zool. ser. 

 1, 1896, p. 10O the writer concluded that the position of this genus is near the Cheloniidae, but 

 with evident relationships to the Chelydridae, constituting a distinct family, which is to be 

 called, as Baur has proposed, Toxochelyidae. This conclusion has been confirmed by more 

 recent investigations made by Case, Wieland, and the present writer. The resemblances to 

 Chelydra are to be found especially in the anterior portion of the skull, in the structure of the 

 carapace, in the humerus and femur, and in the tuberculated tail. 



The roof of the mouth is practically identical with that of Chelydra except that the palatine 

 extends forward to articulate with the vomer in front of the choanae. The masticatory surfaces 

 of the two are equally flat, the cutting-edges of the maxilla are low in both, the choanae are 

 placed well forward and are not underfloored by processes from the palatines; and there are 

 in both genera large palatine foramina. On the other hand, as in the Cheloniidae, the tympanic 

 cavity has not yet entered the squamosal bone, the notch in the hinder face of the quadrate 

 remains open, and the back of the skull is extensively rooft over bv the parietal, postfrontal, 

 and squamosal bones. As regards the carapace, it is evident that the nuchal resembles 

 more that of the Cheloniidae, it having had no such long costiform processes as we find in the 

 Chelydridae. Again in the presence of a surface for articulation with the spine of the eighth 

 cervical, as determined by Wieland, the nuchal resembles more that of the Cheloniidae. There 

 were 1 1 peripherals, as in Chelydra and most Cheloniida;. The costal plates were less developt 

 than in the Chelvdndae, even less than in any living Cheloniidae, so that there are extensive 

 fontanels at the sides of the carapace. The elements in the midline appear to have resembled 

 more those of Chelydra, but there were peculiarities. There was a prominent carina, which at 

 intervals rose into comprest tubercles. The latter were distinct bones, which rested on the 

 contiguous portions of two neurals or suprapygals. The first rested on the first neural; the 

 second, on the second and thud; the third, on the fourth and fifth; the fourth, apparently 

 on the seventh and eighth or on the eighth peripheral and the first suprapygal. If the fourth 

 was placed on the seventh and eighth neurals a fifth tubercle rested on the second suprapygal. 

 Wieland has named these ossicles "epineural spines," but they are hardly to be thus homol- 

 ogized with the epineural bones of fishes. They were continued backward on the upper 

 surface of the tail as a series such as we find on the tail of Chelydra. The position of all these, 

 except the most anterior, was described and figured by the writer in 1898 (Amer. Naturalist, 

 .\x.\11, p. 936, fig. 2). Dr. Case was the first to observe the presence of one of these bones. 

 Wieland in 1905 (Amer. Jour. Sci., xx, p. 331) describes a small bone on the first neural 

 which probably represents the first of this series of ossicles. Wieland in 1896 (Amer. Jour. 

 Sci., 11, p. 400) suggested that Arehelon may have borne a series of dorsal spines; but as those 

 spines were believed to be horn}- and their existence only hypothetical, their discovery has 

 nothing to do with that of the bony spines. The writer has elsewhere presented his reasons 

 for believing that these tubercles represent the original dermal skeleton of the Testudines, 

 now retained only by Dermochelys (Amer. Naturalist, xxxn, 1898, p. 929). 



The writer presents here a description and figures (plate 30, figs. 1. 2) of a portion of a 

 carapace belonging to an undetermined species of this genus, remains which were collected 

 !>v Mr. H. T. Martin in Gove Countv, near Monument Rock, Kansas. Since this carapace 

 was nut accompanied by any part of the skull, it was not possible to identify it specifically. 

 The specimen furnishes 15 peripherals, some fragments of costals, and a series of median 

 elements, of which 2 appear to be suprapygals. The median line of the carapace was occupied 

 by a strong and sharp keel. Anteriorly the right and left sides of this keel make about a right 

 angle with each other, but posteriorly thev meet at a smaller angle, so that the keel is high and 

 sharp. At intervals the keel rises into comprest tubercles. These were in all cases originally 

 distinct bones, but most of them, especially posteriorly, have become co-ossified with the 

 supporting bones. The first neural appears to be wanting, together with the nuchal. There 

 is present I neural which does not furnish satisfactory contact with any of the others. There 



