TRIONYCHID~. 51 
Al 
Amyda? virginiana (Clark). 
Plate 96, figs. 7, 8; text-figs. 670, 671. 
Trionyx virginianus, CLARK, Johns Hopkins Univ. Bull., xv, 1895, p. 4; Bull. No. 141, U. S. Geol. 
Sury., 1896, p. 59, plate viii, figs. 1a, 1b.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 1g02, P- 4553— 
Case, Maryland Geol. Sury., Eocene, 1go1, 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 17 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 
q j O71. 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 
670. Section parallel with intercostal suture. with the sutural border. There area few ridges 
71. Section at right angle with intercostal suture. : 2 e i “5 
8 : 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 4. 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 /. 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 4. virginiana (Clark, fig. 1b) 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 rb 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. 
Fics. 670 AND 671.—Am yda? virginiana. Sections 
Ei v1 
y 
of costal bones of type. 4 
Amyda? cariosa (Cope). 
Plate 86, figs. 9, 10. 
Trionyx cartosus, Cork, 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. 1ooth Merid., 1877, p. 44, plate 
xxvi, figs. 5-10; Vert. Tert. Form. West, 1884, p. 118.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 
1902, p. 453. 
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. 
