282 FOSSIL TURTLES OF NORTH AMERICA. 
estimated by Cope to have been about twice the size of the specimens of 4. ornata that had 
then been found. He concluded that it belonged to a distinct species for the reason that the 
sculpture had not increast in coarseness corresponding to the increase in size of the animal. 
This, however, is not a sufficient reason. Since the bones increase in size by additions to their 
borders, the lines and pits of the sculpture once formed will not change in coarseness. A better 
reason for regarding the bones as those of a species different from 4. ornata is to be found in 
their form. The anterior peripheral, the first of the left side (Cope’s fig. 18), has the form of a 
rhomboid, quite different from that of any anterior peripheral of 4. ornata. The lower side of 
Cope’s figure is that of the free border of the bone. The thickness of the bone is 7 mm. The 
hinder peripheral appears to be the ninth or tenth. It is 7 mm. thick and its free edge is obtuse. 
In 4. ornata, on the contrary, it is acute. 
The length of the anterior peripheral, along the free edge, is 25 mm.; its height is 28 mm. 
Both these dasencionel in the hinder peripheral are 25 mm. Taihe sculpture of the anterior bone 
is stated to consist of closely packt vermicular ridges which run out flat on the posterior and 
upper borders. In the posterior the ornamentation consists of closely placed minute tubercles 
over the whole surface, these being more or less confluent on the posterior and upper borders. 
Mr. R. Lydekker has described and figured a species called Anosterra anglica, trom the 
Lower Oligocene of Hordwell, England (Cat. Foss. Rept., 111, p. 143, figs. 34, 35). Dr. G. 
Baur (Ann. Mag. Nat. Hist., 111, 1889, p. 273) has stated that this can not be distinguisht from 
Cope’s 4. radulina. A glance at the figures of the two forms shows that they can not be 
identical, the sculpture of the English species being far coarser. In 4. ornata the suture 
between the hypoplastron and the xiphiplastron, in crossing from the free border to the mid- 
line, runs first forward, then backward, then forward again. In the English species it runs 
obliquely, but directly, inward and forward. It is not probable that two species of the same 
genus would be so different. 
Genus XENOCHELYS Hay. 
Characters drawn from the type and only known ‘specimen. Neurals 6, the 4 anterior 
having the narrow end directed forward. Only 7 pairs of costals; those of the sixth and 
sev enth pairs meeting at the midline. Ten pairs of peripheral bones, and 11 pairs of marginal 
scutes; the nuchal scute very small. Plastron joined to the carapace without Rae 
Bridge narrow. Only 5 pairs of plastral scutes. “Two inframarginals on each bridge. 
Type: NXenochelys formosa Hay. 
This genus differs from Dermatemys in having no axillary or inguinal buttresses; 5, 
instead of 6, pairs of plastral scutes; and in the es of the anterior neurals. In the reduced 
number of peripheral bones and marginal and plastral scutes it resembles Staurotypus. In the 
latter genus, too, 3 of the anterior neurals have the narrower end directed forward. The 
width of the bridge of Xenochelys is intermediate between that of Dermatemys and that of 
Stauroty pus. The two genera just mentioned, as well as Claudius, the nearest living relatives 
of Xenochelys, are jababicants of Central America. 
Xenochelys formosa Hay. 
Text-figs. 355, 356. 
Xenochelys formosa, Hay, Bull. Amer. Mus. Nat. Hist., xxu1, 1906, p. 29, figs. 2, 3. 
Of this species there is at present known only the specimen which serves as the type. This 
was discovered in the year 1904, at Quinn Draw, Washington County, South Dakota, by Mr. 
Albert Thomson, of the American Museum of Natural History. The deposits in which it was 
found belong to the lower division of the Titanotherium beds of the White River Oligocene. 
The specimen consists almost wholly of the shell, and this is somewhat crusht. The plastron 
is driven upward into the carapace, and a small portion of the left margin of the carapace is 
wanting. The whole structure of the shell can nevertheless be determined. 
The length of the carapace (fig. 355), measured ina straight line, is 200 mm.; the great- 
est width 129 mm. The shell is therefore slightly narrower proportionally than that of 
Dermatemys mawit. The height was moderate. A low rounded carina is found on the nuchal 
