MIOCENE MOLLUSCA AND CRUSTACEA. 91 
° 
duced, compressed, much reflexed; the end acutely rounded.” In his 
observations on it he says the figure there given ‘is only approximate to 
the true outline, as the shell is slightly crushed.” It is true the figure is 
only approximate to the outline of the specimen, but the crushing has been 
so very slight that it forms but little excuse for the imperfection of the outline. 
There is but a single (right) valve of the species for the basis of the above 
descriptions, and no specimen of it has turned up in other collections. I 
can see no reason for the removal of the species from the genus Saxicava to 
Thracia, as the shell does not present the features requisite to the latter 
genus, being entirely destitute of the projecting crescentic ossicle character- 
istic of it. It appears, however, to possess the hinge features of Saxicava 
so far as can be seen from the specimen, which has been cleared out around 
the hinge for the determination of these features. * I can, however, find no 
evidence whatever of the two small cardinal teeth in the right valve spoken 
of in Mr. Conrad’s first description. There may possibly have been one 
very minute tooth, but if so it has been destroyed, and what may have been 
mistaken for a second is only a fracture and slight displacement of the 
shell. The valve may be characterized as follows: 
Shell small, only the right valve known, which is moderately convex - 
and transversely ovate in-outline; the beak, which is proportionally large, 
being situated at about one-third of the length of the valve from the anterior 
end. Anterior end rounded below and obliquely sloping from the beak to 
near the middle of the height on the upper side. Posterior end narrower, 
rounded below and sloping above, a short part of the cardinal border near 
the beak being nearly straight and parallel to the basal margin. Base very 
broadly rounded. Body of the valve gibbose from the beak to the base for 
the anterior half, but recurved posteriorly. Surface marked with distinct. 
concentric lines. The hinge is narrow and obscure, but shows a short nar- 
row ligamental area of attachment posterior to the apex of the shell, and a 
depressed false groove anterior to the beak. 
The hinge of this valve is an exact counterpart of that shown on most 
of the distinctly marked examples of Saxicava rugosa, as seen in both recent 
and post-Pliocene fossil specimens, and shows a very close generic affinity 
with that species. The internal characters of the other portions of the valve 
