ART. 26 A FOSSIL TUETLE LYNN S 



angles to the sutures, the grooves sometimes broken up into pits 

 by cross-ridges. In the best-preserved portions of the carapace this 

 sculpturing is continued quite to the beveled margin of the shell. 

 The width of ridges and grooves is variable, being in general greater 

 toward the posterior end. Thus on the first costal plate five ridges 

 and five grooves are contained in a line 18 mm. long; on the fourth 

 costal the same number is contained in a line 22 mm. long; and on 

 the eighth costal a line 28 mm. long is required. Moreover, the 

 ridges run more irregularly and are more broken up on the anterior 

 costals than on the posterior ones; and in all the costals the sculp- 

 turing is in general much more regular toward the distal ends. 

 Plate 2, upper, shows the sculpturing on a large fragment from 

 the distal end of the fifth costal of the right side. The ridges and 

 pits on the neurals are extremely irregular in arrangement, produc- 

 ing a reticulate apjDearance. These facts indicate that the type 

 fragments do belong to a single species, the difference in sculptur- 

 ing described by Hay being attributable to the differences normally 

 present between distal and proximal j)ortions of the plates. 



Moreover, little doubt remains as to the authenticitj^ of the species. 

 Hay's description of Amy da {Triom/x) cariosa (Cope) shows that 

 it differs considerably not only in length and thickness but also in 

 the sculpturing, for in Amy da cariosa the ornamentation consists 

 chiefly of irregularly arranged pits, whereas in Amyda virginianus 

 long longitudinal grooves predominate. The chief difference between 

 Amyda {Tr'ionyx) fennata (Cope) and the specimen under con- 

 sideration is, as Hay remarks, that in the former the pits " are 

 arranged in rows that run from the sutural edges toward the middle 

 of the bone and at the same time toward the distal end." This is 

 quite different from the condition in Amyda mrgimanus^ where the 

 ridges show no tendency to run toward the distal ends of the bone. 

 Moreover, the fragments of Amyda pennata indicate that it was a 

 much smaller turtle than was the one represented by the present 

 specimen. However, the known fragments of Amyda fennata are 

 so small and so few that it is impossible to clear up this point with 

 absolute finality, although evidence thus far available seems to indi- 

 cate that this species also is distinct from Amyda virginianus. 



BIBLIOGRAPHY 

 Clark, William B. 



Johns Hopkinp ^jniversity Circular, vol. 15, No. 4, p. 4, 1895. 

 U. S. Geol. Survey Bull. 141, p. 59, pi. 8, figs, la and 16, 1896. 

 Hay, Olives: P. 



U. S. Geol. Survey Bull. 179, p. 455, 1902. 



Fossil Turtles of North America, p. 515, pi. 96, figs. 7 and 8, text figures, 

 670 and 671, 1908. 



