5 16 FOSSIL TURTLES OF NORTH AMERICA. 



As regards the thickness, Cope states that one costal was 7 mm. thick at the proximal end, 

 and that others were 11 mm. and 12 mm. thick at the middle of the length and at the distal 

 ends. At the free margins of the costals the upper layer of bone projected far beyond the lower 

 layers, causing, as Cope states, a deep longitudinal grooving of the free border of the carapace. 

 The costals had a width of about 45 mm. at the proximal end and of about 60 mm. at the 

 distal end. In Cope's figures the width of the ridges is exaggerated and the pits are made to 

 appear too abruptly sunken. 



The figures publisht by Cope show that there are on the proximal ends of the costals 

 deeply imprest and irregularly arranged pits, of which there are four or five in a line 20 mm. 

 long. Along the sutural borders of each of the costals there is a smooth strip. More distally 

 the pits arrange themselves in irregular rows, and sometimes coalesce to form furrows, which 

 run parallel with the margin of the carapace. Of these there are about three in 20 mm. In 

 Cope's figure 7 the ridges and furrows are not represented with enough distinctness. On the 

 neurals there was a honeycomb of pits similar to those on the adjacent ends of the costals. 

 Cope says that the hypoplastron in his possession presented a rather irregular reticulate 

 sculpture medially. The element figured as a probable xiphiplastron had a patch of large 

 pits; but this bone is really the left extremity of the nuchal. The figure is inverted. The right 

 extremity of the nuchal is present likewise. 



Fig. 9, plate 86, reproduced from Cope, gives a view, natural size, of a portion of a neural 

 bone, while fig. 10 of same plate shows a fragment of a costal plate. 



A. radula has a style of ornamentation quite similar to that of the present species; but 

 the shell is thinner, and the free margins are beveled off, instead of having the upper layer of 

 bone overhanging the lower layers. 



Amyda? ventricosa (Cope). 

 Plate 98, figs. 1-6. 



Trionyx ventricosus, Cope, Extinct Vert. New Mexico, in Wheeler's Surv. W. 100th Merid., IV, 1877, 

 p. 45; plate lxiv, figs. 7-13; Vert. Tert. Form. West, 1884, pp. 118, 188. Hay, Bibliog. and 

 Cat. Foss. Vert. N. A., 1902, p. 455. 



This species is represented by somewhat more than 25 fragments, which Cope states belong 

 to 3 individuals. Of these fragments, 7 are figured in Cope's work in the Wheeler Survey, as 

 cited above. All these specimens belong to the U. S. National Museum and bear the number 

 1112. Of the pieces figured by Cope, all are present, except the one which furnisht fig. 10 of 

 the plate cited. New figures of these are here furnisht, except of the missing fragment. 



This species was found by Cope in the year 1874, in the Wasatch deposits of Rio Arriba 

 County, New Mexico. 



Fig. 1 of plate 98 (Cope's fig. 13 ) represents the distal end of the left hypoplastron. This 

 bone indicates that the width of the hypoplastron at the narrowest portion was 20 mm., and 

 that the various dimensions of at least the distal end of the bone were about as they are in 

 Platypeltis spinifera. Cope states that the "twin gomphosial processes" were short and stout 

 but these are not figured, and probably were not present on any of the specimens when found. 

 1 he processes referred to separated from each other before they left the edge of the "cal- 

 losities,'' and hence were probably short. The thickness of the bone where these processes 

 part is 10 mm.; at the sutural edge for union with the hyoplastron the thickness is 7 mm. The 

 ornamentation consists of narrow ridges which, near the free border of the bone, curve around 

 mostly parallel with these free borders; elsewhere, they are irregular in their course. These 

 ridges are frequently connected by cross-ridges, and the intervening spaces form pits and short 

 furrows wider than the ridges. Usually there are 2 or 3 pits in a space of about 5 mm. 



Fig. 1 of plate 98 (fig. 12 of Cope) presents the same part as the previous figure, but of 

 another individual; but it offers no peculiar features. The same bone of a third individual 

 was larger, the thickness at the base of the twin processes being 14 mm. Fig. 3 of the same 

 plate (fig. 11 of Cope) is a fragment undetermined as to position, but probably belonging to 

 the plastron. It is about 7 mm. thick. The ridges and pits of the sculpture have no regular 

 arrangement, and the sculpture turns over the edge just below the outstanding process on one 

 side. Fig. 4, plate 98 (fig. 7 of Cope), shows the distal end of a costal plate, including the 



