trionychidj*:. 



523 



are usuallv large, there being 2 in a line 10 mm. long; but on the distal ends there may be 3 

 or 4 pits in this distance. These pits are arranged in somewhat irregular rows across the 

 costal bones. Some of the ridges separating these rows are higher and have sharper summits 

 than the others, these more conspicuous ridges running across the costals at a distance of 

 about 10 mm. apart. There mav thus be from I to 4 rows of pits between each two of these 

 larger ridges. 



Amyda franciscae sp. nov. 

 Plates 102, 103; text-figs. 678, 679. 



The fine specimen to w'hieh the name Amyda franasctc is given was collected by Mr. 

 Walter Granger, of the American Museum expedition of 1903, in the Bridger beds of Wyoming. 

 The exact locality is the eastern part of the Grizzly Buttes; the level is that known as B. The 

 specimen consists of the complete carapace and plastron; the seventh and eighth cervical 

 vertebra?; both scapula; and both coracoids; the pelvis, mostly hidden by the xiphiplastrals; 

 the proximal ends of both humeri; most of the right hind leg; the left femur; and most of 

 the left hind foot. The catalog number of the type is 5936. 



678. 



FlGS. 678 AND 679. Amyda franciscce. X i- 



678. Carapace. 



679. Plastron, ent, entoplastron; epi, epiplastron; hyo, hyoplastron; 



hypo, hvpoplastron; xiphj xiphiplastron. 



In form the carapace (plate 102; text-fig. 678) is broadly elliptical, slightlv truncated in 

 front and more decidedly truncated hehind. Antero-posteriorly the carapace is slightly archt; 



more strongly from side to side. The length in a straight line is 

 315 mm.; the greatest width is 293 mm. 



This species is referred to the genus Amyda because of the 

 presence of 8 pairs of costals and the absence of a preneural. 

 There are 7 neurals, of which the first is very large and the 

 seventh much reduced. The anterior neural is considerably 

 broader in front than behind. The table herewith presents the 

 dimensions of the neurals. The four neurals succeeding the 

 first are wider behind than in front; the next two are wider in 

 front than hehind. 



The nuchal has a fore-and-aft extent of 36 mm., and is about 

 130 mm. from side to side. The anterior border of the bone is occupied by a narrow, smooth 

 band. There appears to have been a small median fontanel between the nuchal and the 

 first neural. 



The form and the relative proportions of the costal plates maybe seen from the illustrations. 

 Their free borders are beveled off to an acute edge. The costal ribs are broad and they project 



