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. 101) the writer concluded that the position of this genus is near the Cheloniidz, but 
with evident relationships to the Chelydrida, constituting a distinct family, which is to be 
called, as Baur has proposed, Toxochelyida. 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 choane. The masticatory surfaces 
of the two are equally flat, the cutting-edges of the maxilla are low in both, the choanz 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 Cheloniidz, 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 by the parietal, postfrontal, 
and squamosal bones. As regards the carapace, it is evident that the nuchal resembles 
more that of the Cheloniide, it having had no such long costiform processes as we find in the 
Chelydride. 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 Cheloniidez. There 
were 11 peripherals, as in Chelydra and most Cheloniide. The costal plates were less developt 
than in the Chelydrida, even less than in any living Cheloniude, 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 third; 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, 
XXXII, 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 Archelon may have borne a series of dorsal spines; but as those 
spines were believed to be horny 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, xxx, 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 
by Mr. H. T. Martin in Gove County, near Monument Rock, Kansas. Since this carapace 
was not 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 they 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 
