FROM THE TERTIARY OF VIRGINIA. 239 
This shell is closely allied to the preceding, but the differences in outline, hinge and 
sculpture separate them. 
FAMILY LITHOPHAGIDA. 
GENUS PETRICOLA. 
P. compressa, Pu. 34. Fra. 15. 
P. testa valde transversd, valde inequilaterali, sub-ellipticd, compressd, postice sub-truncatd, antice rotundatd, tenui, 
striald postice et antice; striis minimis, concentricis; margine basali recto; margine dorsali recto; natibus sub-acutis, 
prominentibus; dentibus duobus, parvis, divergentibus. 
Shell very transverse, very inequilateral, sub-elliptical, compressed, posteriorly sub-truncate, anteriorly rounded, 
thin, striate posteriorly and anteriorly; strie very small, concentric; basal margin straight; dorsal margin straight; 
beaks somewhat acute, prominent; teeth two, small, divergent. 
Diam, .10. Length .12. Breadth .25 of an inch, 
Remarks.—The concentric lines of growth are very small. They are visible on the 
anterior and posterior portions of the shell. On the central part they are obsolete, 
leaving it smooth. The teeth are small and unusually divergent for a Petricola. 
This shell is smaller and more compressed than any of our described species. In 
form it much resembles Saxicava vaginoides, Desh., but it is more transverse and differs 
in the hinge. 
FAMILY NYMPHIDA. 
GENUS PSAMMOCOLA, (BrarnvitiE) 
P. tucinoipeEs, Pu. 34. Fie. 16. 
P. testé sub-orbiculari, pene equilaterali, postice et anticé rotundatd, convexd, tenui, striata; striis concentricis, 
minimis; natibus prominentibus, sub-rectis; valvd sinistrd dentibus duobus cardinalibus, quorum unus bifidus, late- 
vralibus nullis, 
Shell suborbicular, almost equilateral, rounded anteriorly and posteriorly, convex, thin, striate; strim concentric, 
very small; beaks prominent, nearly straight; left valve with two cardinal teeth, one of which is bifid, and no Jate- 
ral ones. 
Diam. .15, Length .31, Breadth .35 of an inch. 
Remarks.—This shell is unusually lenticular for a Psammocola. The concentric 
strie are numerous and extremely small. There are, however, three or four larger ones, 
nearly equidistant, over the surface of the shell. 
The general resemblance which this shell bears to some species of the genus Lucina, 
will readily distinguish it from its congeners, 
I have adopted this genus on the authority of Sowerby, who says that in it Blainville 
unites the Psammobia and Psammotea of Lamarck, considering the difference between 
these genera as artificial and accidental. 
P. rect, Pr. 34. Fre. 17, 
. A xO 8 Fy 
P. testd transversd, ovato-quadratd, inéquilaterali, postice hiante, anticé et posticé subtruncatd, valde inflati, 
, ; ‘4 A . ae * Mi » . . * 2 M s y a” 2 
crassissimd, sulcatd; suleis radiantibus, crebris, equalibus, latis; margine basali pene recto; margine dorsali sub-cur» 
