. Carnegie Institution of Washington publication. TRIONYCHID-ffi. 531 Seen from the suit- the cutting-edge of tlie maxilla is convex from front to the hinder end. The zygomatic arch has only moderate width. The tympanic cavitv did not extend so far backward into the squamosal as it does in P. ferox and P. spinifera. Until we shall have secured the carapace of this species in association with the skull, we must remain uncertain as to the genus to which it belongs. Amyda egregia sp. nov. Plate 107, figv. I-;; text-fig. 6ql. I he type of this species is a complete carapace which was collected in
. Carnegie Institution of Washington publication. TRIONYCHID-ffi. 531 Seen from the suit- the cutting-edge of tlie maxilla is convex from front to the hinder end. The zygomatic arch has only moderate width. The tympanic cavitv did not extend so far backward into the squamosal as it does in P. ferox and P. spinifera. Until we shall have secured the carapace of this species in association with the skull, we must remain uncertain as to the genus to which it belongs. Amyda egregia sp. nov. Plate 107, figv. I-;; text-fig. 6ql. I he type of this species is a complete carapace which was collected in 1895, by Mr. C). A. Peterson, in charge of the American Museum expedition of that year. It was obtained from the lower Washakie beds, south of Haystack Mountain, Wyoming. The number is 1186. The shell (plate 107, fig. 1; text-fig. 691) is broad, rounded m front, truncate behind, and moderately convex. The border is slightly emarginate on each side at the suture between the nuchal and the first costal plate; elsewhere gently repand. The length of the carapace, in a straight line, is 356 mm.; the great- est width is 334 mm. Of neural plates there are seven present. The table gives then dimensions. The first neural is only 25 mm. wide at its hinder end. The nuchal has a trans- verse extent of 150 mm. and measures fore and aft 22 mm. Its outer extremity overlaps the free end of the rib of the first costal plate. The shell of this species is quite thick and solid. The thickness of the fifth costal plate, a little beyond the middle of the length and at the sutural edge, is about 10 mm.; in the middle of the width, where the rib lies, the thickness equals 15 mm. The ribs do not appear to have projected much beyond the margin of the carapace, apparently only about 30 mm. At the margin the shell is beveled off rather abruptly, but the sculptured layer nowhere projects beyond the deeper layers of bone. On the front of the nuchal the bevel of the margin becomes a broad shallow groove. The
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