532 



FOSSIL TURTLES OF NORTH AMERICA. 



Amyda crassa sp. nov. 

 Plate 108; text-fig. 692. 



This species is founded on a fragmentary carapace, No. 3887 of the American Museum of 

 Natural History. This was collected bv that museum's expedition of 1895, in the upper beds, 

 "horizon C," of the Uinta deposits, in the region along White River, Utah. The parts present 

 include a considerable portion of the costals, a few of the neurals, and nearly the whole of the 

 nuchal. Most of the left second costal is missing, about the distal half of the right third, 



portions of both costals of the fourth pair, and practically 

 all of those behind the third of the right side. There is also 

 at hand a portion of a plastral bone of another individual, 

 probably of the same species; and this is labeled "top of 

 B, Uinta." 



In form the carapace (plate 108; text-fig. 692) is broadly 

 oval, with the length exceeding the breadth, and with the 

 greatest width at the middle of the length. The length is 

 475 mm.; the extreme width, 420 mm. The anterior 

 border is regularly rounded, while the hinder border is 

 rather truncated. The carapace was apparently only 

 moderately convex. There were 8 pairs of costal plates 

 and 7 neurals. 



This species is remarkable for the thickness of the 

 bones of the carapace, and for the coarseness of the sculp- 

 ture, equaling and even surpassing in these respects any of 

 the species of the Wasatch deposits. The usual thickness 

 of the costals is, near the sutural borders, 10 mm.; thru 

 the middle of the width, 13 mm. The thickness of the outer 

 end of the nuchal is 18 mm. The sculpture consists of 

 ridges and pits, usually very irregular in form and size and 

 arrangement. The largest pits may be 8 mm. across; but 

 there are commonly 2 in about 10 mm. The ridges sepa- 

 rating them may be as broad as the pits, but more often 

 they are narrower and rather sharp. Their elevation like- 

 wise varies greatly. On the proximal ends of the costals there is little or no regularity in their 

 disposition, but toward the distal ends the pits and ridges are arranged in rows running across 

 the costals. 



The nuchal bone of this species resembles that of A. uintaensis (Leidy), described and 

 figured in this author's Contributions to the Extinct Vertebrata of the Western Territories, 

 p. 178, plate xxix, fig. 1. Its length from side to side is not far from 275 mm., while its fore- 

 and-aft extent is 58 mm. It is pointed at the outer ends. There were no fontanels between it 

 and the first neural and the first pair of costals. There is a shallow groove, about 10 mm. 

 wide, running along near the anterior border; and this border is beveled so that the upper sur- 

 face somewhat overhangs the lower. 



The free borders of the two anterior costals and of the more posterior ones are rounded 

 off, but the intermediate ones are beveled. The first costal is very broad, about JJ mm. across 

 the middle. The succeeding ones up to and including the fifth are considerably narrower, 

 about ^> mm. The sixth is 47 mm. wide at the proximal end, while its distal end is about 80 

 mm. I he width of the seventh at the proximal end appears to have been about 36 mm., 

 while the outer end, measured along the oblique free border, is 60 mm. 



< )nlv a few neurals are present, and none of these is complete. Nearly the whole of the 

 first is present. It is coffin-shaped, and the front end is convex. The length was close 1070 mm.; 

 the width ot the anterior end, 56 mm.; that of the widest part, near the hinder end, 52 mm. 

 ( >t the (onus and dimensions of the second, third, and fourth neurals, we can judge only 

 from the spaces which intervene between their contiguous costals when these are in place. 

 They were all smaller than the first, but of the same general form. The second, about whose 

 dimensions we can be most certain, had a length of 57 mm., and a width at the hinder and 

 wider end ot 43 mm. The fifth neural is present only in part. Its length appears to have been 



FlG. 6y2. Amyda crassa. Cara- 

 pace of type. X5. 



