BKACI1I0P0DA. 
31 
The surface is radiated by fine ribs, which are close, equi¬ 
distant, and interlined by other and similar ones; and there are 
a few silky striae between these, but only near the margin. 
The muscular impressions (cardinal muscles) are very long, 
reaching two-tliirds down the shell, forked almost from the 
beak, and thence diverging at 35 degrees. The separate scars 
are narrow, linear, and obliquely truncate. At the ends a 
strong crescentic groove, notched on the median line, circum¬ 
scribes the visceral portion, but is only seen in full-grown 
specimens. 
The dorsal valve is radiated in the same way. It has a 
slight depression from the beak outwards, corresponding to the 
elevation in the other valve. It is regularly concave, not 
abruptly bent in any part. We have not the interior. 
This is rather a large and convex species of a genus, which 
is, so far as I know, confined to the Silurian beds. L. sericea , 
L. transversalisy and many other species, resemble it, but none 
that I know agrees with it quite. 
Locality .—Chorhoti Pass (1754),abundant. At Bompras, 
16,000 feet high (1663). Milam Glacier (931). Kalajowar; 
Upper Rimkin; Gunesgunga. 
LEPTiSNA NUX. 
Plate 4, fig. 2. 
L. vix semiuncialis, oblongn,—cardine production, valvis in¬ 
volute, longis, striatis. Valva major gibba cucullata, longa quam 
lata, umbone obtuso. Valva dorsalis brevior, latior, profunde con- 
cava, area magna parallela. 
A small species, nearly half an inch long, sometimes of an 
oblong, sometimes of a semi-oval shape, not much longer 
than broad, but apparently so; with the ventral valve very 
convex, even gibbous in a longitudinal direction,—the dorsal 
valve deeply and abruptly concave. 
The larger valve, which has a greatly curved and overhang¬ 
ing blunt umbo, has the hinge line somewhat broader than 
