TRIONYCHIDA. 509 
described and figured the dermal scutes of a dinosaur, Nodosaurus textilis, which are markt 
by similar, but coarser, interwoven bony fbers 
However, since there appears to be an unusual abundance of this layer of fibers and a 
nearly complete absence of the sculptured layer, the so-called callosities, it appears advisable 
for the present, to retain the species in a distinct genus. There are reasons for believing that 
the nuchal bone also will offer some characters when it is completely known. 
Axestemys byssina (Cope). 
Plate 104, fig. 4; text-figs. 668, 669. 
Axestus bysstnus, Corr, Proc. Amer. Philos. Soc., x11, 1872, p. 462 (4. bystmus, misprint); U.S. Geol. 
Sury., 6th Ann. Rep., 1872 (1873), p. 616; Vert. Tert. Form. West, 1884, p. 116, plate xv, figs. 1-12. 
Axestemys byssinus, Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 455; Amer. Geologist, xxxv, 1905, 
P- 337: 
The type of this species, now in the U. S. National Museum at Washington, has been 
studied by the present writer. The type was found on Black’s Fork of Green River; the second 
specimen on upper Green River. Both probably belong to level B. These bones were figured 
by Cope in his great work The Vertebrata of the Tertiary Formations of the West, the 
figures having half the size of nature. These bones are from 2. 33 to3 times as large as the cor- 
responding ones of a specimen of Platypeltis whose carapace is 147 mm. long. The animal 
therefore had a carapace probably over 420 mm. in length. 
The xiphiplastron (plate 104, fig. 4; text-hg. 668) difcrs from that of Platypeltis spinifera 
in having the posterior process narrower and more elongated and in having the callosity wholly 
devoid of the layer which ordinarily furnishes the sculpture, but composed of a layer of 
textile-like fibers of bony tissue. The thickness of the central portions of this bone is 10 mm., 
that of the living species just referred to being about 3 mm. Hence the thickness of the 
plastron of the fossil species under consideration is proportionally as great. The greatest 
length of the fragment of xiphiplastron is 166 mm. It probably had a length originally of 
188 mm. The shoulder-girdle seems not to have differed in any important respect from that of 
Platypeltis spinifera. The humerus, so far as represented, is like that of the living species 
referred to, except that the head appears to have been more narrowly oval, with the plane 
thru the long axis parallel with the long axis of the shaft of the bone. 
The femora are like those of Platypeltis spinifera, except that there is a very distinct ridge 
on the middle of the upper surface of the distal half of the shaft. The pelvis appears not to 
have offered any difference worthy of mention. The cervical vertebra which has been preserved 
is certainly the seventh, agreeing in every way with that of Platypeltis spinifera. Its centrum 
is just 3 times as long as that of the corresponding cervical of the specimen of Platypeltis 
referred to above. 
Professor Cope mentioned another bone, a hypoplastral, which, on account of its great 
thickness, he thought might belong to a distinct species. This bone is now in the possession 
of the American Museum of Natural History and bears the number 1034. Its greatest thick- 
ness, about the middle of the bone, is 14 mm. and this is not so much greater than that of the 
xiphiplastron that it can not belong to the same species. The lower surface is like that of the 
xiphiplastron of the type. The form of this bone does not differ from that of the same bone of 
Platypeltis. 
The American Museum also possesses a number of bones which include the greater 
portion of the left half of the nuchal, most of the left first costal, fragments of ever other 
costals, and a fragment of plastral bone. They bear the Museum’s number 1046. The 
nuchal bone shows ; conclusively that the species 1s not T. scutumantiquum, which is suggested 
by the character of the sc ulpture; while the remains of the plastron prove that they Belo to 
Axestem YS. The latter are thick, and hence are undoubtedly of the same species as the thick 
hypoplastral mentioned by Cope. Until additional materials are forthcoming we may refer 
them to 4. byssina. The piece of the plastron of No. 1046 is about 8 mm. thick. near the base 
of one of the processes directed toward the midline, and the lower surface has the textile-like 
surface of the type specimen of the species. The portion of the nuchal (fig. 669) remaining has a 
fore-and-aft extent of 53 mm. and a total lateral extent of 102 mm. The mesial end approaches 
