. Carnegie Institution of Washington publication. 250 FOSSIL TURTLES OF NORTH AMERICA. surface of the plastron appears to have been somewhat uneven, but no definite pattern of sculpture can be made out. The fourth neural (plate ^j, fig. 5) has a length of zj mm., a width of about 24 mm., and a thickness of 11 mm. The costals at the proximal ends are as thick as the neurals, but they rapidly become thinner, so that at a distance of 30 mm. from the neurals a costal is only mm. thick; and this thickness is maintained to the distal ends. The capitula of the ribs are well developt. The sulci li
. Carnegie Institution of Washington publication. 250 FOSSIL TURTLES OF NORTH AMERICA. surface of the plastron appears to have been somewhat uneven, but no definite pattern of sculpture can be made out. The fourth neural (plate ^j, fig. 5) has a length of zj mm., a width of about 24 mm., and a thickness of 11 mm. The costals at the proximal ends are as thick as the neurals, but they rapidly become thinner, so that at a distance of 30 mm. from the neurals a costal is only mm. thick; and this thickness is maintained to the distal ends. The capitula of the ribs are well developt. The sulci limiting laterally the vertebral scutes are deeply and sharply imprest. These vertebral scutes were rather narrow, about 43 mm. wide. The third vertebral has a length of 60 mm. The surface of the bone is finely striated longitudinally. Plate 37, fig. 4, represents 3 peripherals which appear to have had the positions assigned to them, the eighth, ninth, and tenth of right side, but possibly the ninth, tenth, and eleventh. The one seen on the right of the figure is the anterior, but it did not articulate with the hypoplastron. Each has an extreme thickness of about 1 1 mm. The exterior surface is con- cave vertically, while the inner surface is strongly convex. Fig. 310 is a section through the middle one of the three. Altho the free edge of the series is somewhat eroded, it evidently was rounded. Further forward this edge appears to have been more angulated, until, as represented by one of the bridge peripherals, the upper side of the shell made abruptly an angle of about 45° with the lower side. The marginal scutes of this species were confined to the peripheral bones, instead of extending upward on the costals. As shown in the figures, the costal scutes come down well on the peripherals. The carapace of this species had a length of about 265 mm. In the Cope collection at the American Museum there is a pair of hyoplastrals, No. 1479 (plate 37, fig. 2), which evidently belongs to
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