rRIONYCHID I . 



515 



FlGS. 670 and 671. Amydai virgintana. 

 of costal bones of type. X A. 



Sections 



670. Section parallel with intercostal suture. 



671. Section at right angle with intercostal suture. 



Amy da? virginiana (Clark). 



Plate 96, figs. 7, S; text-figs. 670, 671. 



Trionyx virginianus, CLARK, Johns Hopkins Univ. Bull., xv, 1895, p. 4; Hull. No. 141, U. S. Geol. 

 Surv., 1S96, p. 59, plate viii, tigs, la, lb. Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 455; 

 Case, Maryland Geol. Surv., Eocene, 1901, p. 97, plate xi, figs. I, 2. 



All the known specimens of the present species were found at Aquia Creek, Virginia, in 

 Eocene deposits belonging to the Aquia Creek stage. The type fragments consist of a portion 

 of the distal end of a costal plate and of what appears to be the proximal end of another costal, 

 but which is possibly the outer end of the left hypoplastron. 



The first-mentioned fragment represents 

 about half of the width of the costal. Figure 

 670 shows a section along the broken edge, 

 the distal end being toward the right. At the 

 proximal end the fragment is \~ mm. thick. 

 Toward the distal end this increases to 26 mm., 

 then drops off suddenly to half the latter 

 thickness, then runs out to a thin edge. At the 

 sutural border the thickness is slightly greater 

 than at opposite points on the broken border. 

 This shows that there is no ridge produced by 

 the rib. The sculpture (plate 96, fig. 7) con- 

 sists of ridges and grooves placed at right angles 

 with the sutural border. There are a few ridges 

 crossing the grooves, breaking them up into 

 circular and elongated pits. Five pits and as many ridges are found in a line 22 mm. long. 

 Toward the line where the thickness is suddenly reduced the sculpture becomes obscure. 

 There is no smooth band along the sutural border. 



The pits of this costal have the same size as in A. pennata (Cope), of the Eocene of New 

 Jersey. However, in the latter 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. In A. pennata the 

 rib produces a decided thickening on the under side of the distal end of the costal. 



The second piece (plate 96, fig. 8) of the type of A. virginiana (Clark, fig. lb) has a 

 thickness of 13 mm. at the distal end of the bone, increasing toward the other end to 15 mm. 

 Fig. 671 is a section across this bone. From the sutural border the bone increases to 22 mm. 

 thickness, an increase due to the presence of the rib on the under side of the bone. This costal 

 plate appears to have been about 80 mm. wide. An objection to regarding this fragment as 

 the outer end of the left hypoplastron is the fact that the ridge runs parallel with the sutural 

 border, instead of approaching it in one direction. 



The sculpture of this fragment differs from that of the other in having the ridges con- 

 siderably broken up and quite irregular in direction. The pits are slightly larger, there being 

 5 of them in a line 25 mm. long. Along the sutural border there is a band 15 mm. wide which 

 is markt only by striations at right angles with the sutural edge. It is possible that in these two 

 fragments we have two distinct species. 



Amyda? cariosa (Cope). 

 Plate 86, figs. 9, 10. 



Trionyx cariosus, Cope, Syst. Catalogue Vert. Eocene, New Mexico, 1875, p. 35; Ann. Rept. Chief of 

 Engineers, 1875, p. 1025 (of separata, p. 95); Wheeler's Surv. W. 100th Merid., 1877, p. 44, plate 

 xxvi, tigs. 5 10; Vert. lift. Form. West, 1X84, p. 118. Hay, Bibliog. and Cat. Foss. Vert. N. A., 

 1902, p. 45.?- 



The type specimens of this species are in the U. S. National Museum at Washington, and 

 have the catalog number 2575. Those which Cope figured consist of fragments of costal 

 bones, 1 neural, and a supposed xiphiplastral. Cope mentions also a hypoplastral as being 

 among his materials. The species is characterized by the coarse sculpture, the thickness of 

 the bones, and the longitudinal grooving of the margins of the carapace. The type was found 

 in the Wasatch beds of New Mexico, by Professor Cope, in 1874, along the Gallinas River. 



