GILMORE: the fossil turtles of the UINTA FORMATION 155 



the costo-peripheral suture, and the presence of a divided supracaudal scute, in- 

 dicate its relationship with the genus Hadrianus, as now understood and defined. 

 On the other hand, the greatly reduced heads of the ribs, and especially the high 

 degree of differentiation reached by the neural and costal bones show its affinities 

 to Testudo. 



In an attempt to find characters other than those used to separate the three 

 important genera constituting the family Testudinidse I have determined the width 

 of the bridge as compared to the total length of the plastron in all available speci- 

 mens pertaining to the genera Hadrianus, Stylemys, and Testudo, and find the 

 average to be as follows: In Hadrianus the bridge is thirty-eight per cent, of the 

 length of the plastron; in Stylemys it is forty-nine per cent., and in Testudo forty-four 

 per cent. In Testudo uintensis it is forty per cent, thus again demonstrating its 

 intermediate stage of development between Hadrianus and Testudo. 



Cope assigned as the principal character distinguishing Hadrianus from the 

 other genera of the Testudinidse, "a divided supracaudal scute," and this would 

 perhaps appear a good reason for assigning the present specimen to that genus if it 

 were not known that three living species of the genus Testudo as recognized by 

 Boulenger, also have this scute divided. In the definition of the genus Testudo 

 the lip is "usually projecting abruptly from the general contour of the lobe." 

 The present specimen, however, is one of the exceptions, resembling the Oligocene 

 Testudo amphithorax in this respect. 



It will be seen from this brief discussion that the present means of separating 

 the genera Hadrianus and Testudo is very unsatisfactory, and it would perhaps be 

 best to combine them until clean cut characters are found, to show that there are 

 two distinct genera. 



Family TRIONYCHID.E Bell. 



The soft shelled Trionychidis are represented in the present collection by 

 thirteen specimens of the genus Amyda, four of which have been identified specif- 

 ically. These pertain to two species, hitherto known only from the Bridger 

 formation. Two fragmentary specimens, C. M. Nos. 2396 and 3285, judging 

 largely from the character of the sculpturing of the parts of the carapace present, 

 appear to represent undescribed species, but on account of their inadequate nature 

 I refrain from naming them. The genus Amyda is now represented in the Uinta 

 formation by the following species, Amyda crassa Hay, A. egregia Hay and A. 

 scutumantiquum (Cope). 



