CORBULA. DIMYARIA 109 
They are rare in a fossil state, and the species figured is met with in the 
Suffolk Crag. 
Genus XLII.— SAXICAVA. — Lamarck. 
Generic Character. — Shell transverse, irregular in 
form, generally oblong, inequilateral, subequivalve, gaping 
anteriorly ; ligament exterior ; two lateral muscular impres- 
sions in each valve, pallial impression interrupted but not 
sinuated ; hinge in the young condition, with sometimes 
two or three minute, obtuse, mostly indistinct cardinal 
teeth, which become obsolete in the adult, 
Saxicava rugosa. Plate IX. fig. 21. 
The Saxicave are marine shells, and seem principally confined to tempe- 
rate climates, they burrow in wood, clay or limestone, and other soft rocks. 
Fossil species are met with in the Suffolk Crag, and newer formations, 
TRIBE ITI.— CORBULACEA. 
Shells inequivalve ; the ligament interior. 
Genus XLII. —PANDORA. — Bruguiere. 
Generic Character. — Shell free, thin, internally pearla- 
ceous, inequivalve, transverse, inequilateral, the anteriorside 
the longer, subrostrated and slightly gaping at its extremity ; 
one valve flat, with two internal anterior ribs, and with its 
anterior margin turned downwards, provided with a single 
oblong, obtuse cardinal or hinge-tooth, situate behind the 
ligament ; the opposite valve concave and destitute of 
teeth, but furnished with an indistinct cicatrice on which 
the tooth of the flat valve rests, when the shell is closed; 
in each valve are two distant, lateral muscular impressions, 
ligament internal, its sides lodged in, and attached to an 
elongated cicatrice, which lies inclined to the anterior side 
of the valves ; in some species the cicatrice is produced 
into an elongated divergent lamina, stretching from the 
umbo towards the anterior side of the shell, and terminating 
near the inner side of the anterior muscular impression, 
Pandora Defranci. Plate X. figs. 8, 9. 
This genus is distinguished from Tellina by its internal ligament, and from 
Corbula by its single obtuse tooth in one valve only, 
The Pandore are marine shells; and have been found in a fossil condition, 
in the Calcaire-grossier. 
Genus XLIV. — CORBULA. — Bruguiere. 
Generic Character. — Shell inequivalve, one valve being 
generally small and flattened, the other large and convex; 
