DERMATEMYDID^E. 263 



The surface of the bones of the plastron appears, for the most part, to have been smooth, 

 but there are some indications of the same kind of wrinkling, or folding, as is seen on the upper 

 surface. This is especially the case on the bridges and lower ends of the bridge peripherals. 



Genus HOPLOCHELYS nov. 



Shell thick and solid. Peripherals united to the plastral bones by means of digitations 

 and dentated sutures; with the costals by gomphosis and in addition by simple apposition or 

 sutures. Carapace furnisht above with three carinae. Plastron with anterior lobe immovable 

 and with the posterior lobe narrow. 



Type: Chelydra crassa Cope. 



The characters of this genus are derived wholly from the shell. The plastral structures 

 are not well known in any of the species. The genus appears to be related to Staurotypus 

 now living in Central America. The latter possesses only 10 peripheral bones on each side. 

 It appears not improbable that H. sallens and H. paludosa, having the peripherals sutured 

 to the costals, really belong to a distinct genus. 



Hoplochelys crassa (Cope). 

 Plate 38, figs. 4-9; text-fig. 325. 



Dermatemys sp., COPE, Proc. Amer. Philos. Soc., XX, 1882, p. 461 (no description). 



Chelydra crassa, COPE, Science (i), xi, 1888, p. 198 (no description); Trans. Amer. Philos. Soc., (2,) 



xvi, 1888, p. 306. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 446. 

 Hoplochelys crassa, HAY, Amer. Geologist, xxxv, 1905, p. 339. 



Professor Cope's first description of this species appeared in the Transactions of the 

 American Philosophical Society as cited above; but he had previously mentioned it, as early 

 as the year 1882, as a species of Dermatemys. In no place does this author state the exact 

 locality or level at which the specimens were found by his collector, Mr. David Baldwin. 

 However, Cope's label, which accompanies the type specimen, states that it was found June 

 6, 1883; and Dr. W. D. Matthew has been able to show from the labels found with the mam- 

 mals collected by Mr. Baldwin that at that time the collector was in the neighborhood of 

 Chaco Canyon, San Juan County, New Mexico. Both the Puerco and the Torrejon are 

 found in that region and it is therefore uncertain to which of these the fossil belongs. Two 

 other species referred to the genus come from the Torrejon. Cope's first mention of the 

 species in 1882 was doubtless based on other specimens, possibly the three neurals of which 

 he speaks in his description. 



Cope states that he possest remains of 2 individuals. Of the first there were present 2 

 vertebral bones, 9 peripherals, and 3 plastrals; of the second, 3 vertebrals. The bones of the 

 first-mentioned individual are now in the American Museum of Natural History and bear the 

 catalog number 6091; where the remains of the second specimen are is not at present known. 



Of the 9 peripherals in Professor Cope's possession 4 are represented by only as many 

 fragments. No neurals are present, but there are 2 fragments of costal plates (plate 38, fig. 8), 

 which are not mentioned by Cope; unless, indeed, they were mistaken for neurals. A study 

 of the materials at hand has convinct the writer that Professor Cope was nearer the truth 

 when he regarded this species as a Dermatemys. 



As stated, no neural bones are preserved. The presence of a median keel must rest on 

 Cope's statement and on the probability that such a keel would accompany the lateral keels. 

 The latter were sharply defined (plate 38, fig. 8) and ran longitudinally at a distance of about 

 10 mm. from the median border of the costal scutes. Along this keel, on the hinder portion 

 of the costal scute represented, the crest rises but little above the surface of the bone; but 

 immediately behind the sulcus that separates this scute from the next one there is a sudden 

 depression of the bone, so that the keel stands up very prominently. As it is followed back- 

 ward its apparent height diminishes. Where the sulcus crosses the keel the sulcus bends 

 forward, then again backward, thus forming a sort of loop. One of the costals present is 20 

 mm. wide, the other is 18 mm. The thickness through the keel is 6 mm., but this rapidly 

 diminishes to about 3 mm. distally. The width of the vertebral scutes can not be determined. 



