A NEAELY COMPLETE CARAPACE OF A FOSSIL TUR 1 LF, 

 AMYDA VIRGINIANA (CLARK) 



By W. Gardner Lynn 



Of the Johns Hopkins University 



The species Amy da virginiana was first described under the name 

 Trionyx virginianus by Dr. William Bullock Clark in 1895 from 

 fragments found at Aquia Creek, Va., in Eocene deposits of the Aquia 

 Creek stage. On a recent trip to this same locality a nearly com- 

 plete carapace referable to this species was obtained; and since this 

 is, so far as can be ascertained, the most complete specimen of this 

 large fossil turtle yet discovered it seems worthy of description. 



The type fragments of the species were described by Clark as 

 follows : 



Fragments of costals with tuberculated surfaces characteristic of the genus 

 Trionyx. The longitudinal ridges are prominent, at times irregular and in- 

 osculate ; relatively remote and separated by intervals about twice their width, 

 generally entirely disappear near the margins of the plates. 



A number of fragments of the plates of this large species were found in the 

 vicinity of Aquia Creek, Va. This species shows some points of similarity with 

 T. cariosus (Cope), from the Eocene of New Mexico, but is undoubtedly a 

 different form. 



Dimensions. — Length of largest fragment, 130mm. ; width, 45mm. ; thick- 

 ness, 18mm, 



Hay, in his Fossil Turtles of North America, gives more detailed 

 descriptions and measurements of the 2-type fragments which, he 

 believes, indicate a possibilitj^ that the two represent distinct species. 

 This idea is based upon the fact that the sculpturing of the two frag- 

 ments differs. The first fragment (the distal portion of a costal) 

 (pi. 2, center) shows rather regular sculpturing, which consists of 

 ridges and grooves, five of which are found in a line 22 mm. long. 

 The sculpturing of the second fragment (the proximal portion oi: a 

 costal) (pi. 2, lower) is more irregular and the pits are somewhat 

 larger, five being contained in a line 25 mm. long. Moreover, Hay 

 notes resemblances to Amy da pennata (Cope) of the Eocene of New 

 Jersey, although he does not seem to believe that the two are synony- 

 mous. However, it is clear that the position and even the authen- 

 ticity of this little-known species is much in question, and it is 



No. 2823.— Proceedings U. S. National Museum. Vol. 76, Art. 26] ;. 



74736—29 



