524 



FOSSIL TURTLES OF NORTH AMERICA. 



beyond the margin of the carapace about 30 mm. The thickness of the costals, measured at 

 the sutures, is about 8 mm.; measured thru the ribs it is about 13 mm. The costals of the 

 seventh and the eighth pairs meet their fellows along the midline. Those of the eighth pair 

 are rather small. 



The sculpture of the carapace is of median coarseness, there being about 3 pits in a line 

 10 mm. long. The pits are shallow and the rounded walls surrounding them are about as 

 wide as the pits. For some distance on each side of the midline the sculpture is nearly obsolete. 



The plastron (fig. 679) incloses large median fontanels. The entoplastron and the epi- 

 plastra are slender bones, resembling those of Platypeltis spinifera. They possess no "cal- 

 losities." Nearly the whole surface of the hyoplastra and the hypoplastra is furnisht with pits 

 and ridges, but these are not so coarse as those of the carapace, there being about five pits in a 

 line 10 mm. long. These are better developt on the outer ends of the bones mentioned. The 

 median borders of these bones show a band consisting of a network of bony fibers. The 

 surfaces of the xiphiplastra present a similar interlacement of bony fibers. 



The width of the bridge, where narrowest, is 51 mm., of which 26 mm. belong to the 

 hypoplastron. The median border of this bone possesses about ten digitations, of which the 

 two posterior are the largest and receive between them the inner process of the xiphiplastron. 

 The xiphiplastra are slender bones. They join each other by means of anterior two-tootht 

 processes and by broad posterior processes. 



The bones belonging to the vertebral column, the shoulder and pelvic girdles, and the 

 limbs present no peculiarities. 



This species resembles in some respects Amyda uintaensis Leidy. It differs, however, in 

 being more elliptical in outline, in having the greatest width nearer the middle of the length, 

 7 neurals instead of 6, a differently formed first neural, a sculpture finer and of different 

 character, and a narrower plastral bridge, of which the hypoplastron is wider than the hyo- 

 plastron. 



Dedicated to the writer's daughter, Miss Frances Steele Hay. 



Amyda salebrosa sp. nov. 

 Plate 104, fig. i; text-fig. 680. 



Amyda salebrosa is based on a specimen which was collected by Mr. Walter Granger at 

 Dry Creek, in southwestern Wyoming, June 30, 1904. The level at which it was found is C, 

 the middle of the Bridger deposits. Only the carapace is present, but this is practically com- 

 plete. It bears the number 3941 of the American Museum's catalog. 



The carapace (plate 104, fig. I; text-fig. 680) was broad and probably rather flat. The 

 front margin is broadly rounded, the rear truncated. The length is 425 mm.; the greatest 

 width, 455 mm. Considering the great size of the carapace, it is rather thin, being only 8 mm. 

 thick at the sutural borders, near the ends of the costals. Thru the ridges on the underside 

 of the carapace, produced by the ribs, the thickness is 12 mm. The outer ends of the costals 

 are beveled off from above. 



The nuchal has a lateral extent of 267 mm., and a fore-and-aft extent of 57 mm. Its whole 



upper surface is pitted. Its outer ends overlap the outer anterior 

 angles of the first costals. 



There are 7 neural plates, and these decrease in size from the 

 first to the last. The accompanying table gives the dimensions. 

 The first neural is hexagonal, with the short sides consisting 

 of the posterior and the two postero-lateral. The next two 

 neurals have the narrow end directed forward; the fourth is 

 nearly a parallelogram; the fifth and the sixth have the wider 

 end in front; the seventh is pentagonal. The costals of the 

 seventh pair join in the midline behind the seventh neural. 

 Those of the eighth pair met along the midline for a distance of 

 about 30 mm.; and each had a lateral extent of about 48 mm. The distal ends of the ribs pro- 

 ject but little beyond the borders of the disk. In younger specimens they will doubtless be 

 found to project a greater distance. 



