133 
and its surface less marked; the right valve moderately convex. 
The aspect of this shell approaches that of Gervillia, especially 
in those instances where the posterior wing is shorter than 
usual. The right valve also resembles that of Pteroperna 
pygmen, Dunker, but the posterior wing is more produced than 
+n Gervillia, and less than in P. pygmea. Length 15 lines. 
Geological position and locality, the Clypeus Grit of Rod- 
borough Hill, where it is common. 
Tsoarca cyypuaTa. PI. V, fig. 3, 8a, 3b. 
Shell suborbicular, convex, sub-equilateral, umbones moder- 
ately large, slightly curved, sub-mesial. The surface has 
closely arranged concentric lines, with folds of growth; the 
latter become larger near the base of the shell. These are 
crossed by numerous regular lines radiating from the umbones. 
Geological position and locality, the Clypeus Grit of Rod- 
borough Hill, where it is very rare. 
Carprom coenatum. Phil. var. Clypeatum. PI. V, figs. 5, 6. 
This is a variety of the Inferior Oolite shell described by 
Dr. Lycerr, in his Supplementary Monograph of the Great 
Oolite Mollusca Paleont. Soc. 1863, p. 54, Compared with the 
typical form it is distinguished by the greater thickness of the 
shell and prominence of the ornamentation. In the Cornbrash 
and Kelloway Rock of Scarborough the test is delicate, smooth, 
and shining. 
Geological position and locality, the Clypeus grit of Rod- 
borough Hill. 
Asrarrr DEPRESSA, Gotpr. Var. Depressior. Pl. V, figs. 7, 
7a, b. 
Shell sub-orbicular, thin, greatly depressed, umbones ante- 
rior, small, obtuse, nearly flat, lunule obsolete, base regularly 
rounded, cost (about 22) closely arranged, slightly angulated, 
the interstitial spaces with numerous minute concentric striz. 
This shell differs in several respects from A. depressa figured 
by Goldfuss T. 134 f. 14. The umbones are more anterior, and 
L 
