BIVALVIA. 167 
the exterior is more finely ridged over the centre, but the anal ridge beyond the siphonal 
slope is naked. 
Fig. 12, Pl. XXIV, represents a shell from Bracklesham, called by Mr. Edwards 
planiuscula. This is more elongated, more inequilateral, and more compressed, and 
covered with finer and sharper ridges. When more specimens are found it may probably 
prove to be distinct. For the present I have inserted it here as a variety. 
7. CrassareLua piicata, J. Sowerby. Pl. XXIII, fig. 14 a, 6. 
CRASSATELLA PLICATA, J. Sow. Min. Conch., pl. 345, fig. 2, 1822. 
— —  WNyst. Coq. Foss. de Belg., p. 85, pl. xhi, fig. 3, 1843. 
Spec. Char. Cr. Testa transversd, elongato-trigond, inequilaterali, compressiusculd ; 
pedi-regione altiore ; alterd elongatd et truncata ; extus sulcatd, sulcis posticis evanescenti- 
bus ; umbonibus minimis acutis, depressiusculis ; lunuld ovatd, profundd ; siphoni-regione 
depresso, lanceolato ; cardine angusto ; dentibus parvis, simplicibus ; marginibus in medio 
tenuiter crenulatis. 
Shell transverse, elongately trigonal, imequilateral, somewhat compressed; pedal 
region the higher; siphonal side produced and truncated, covered externally with con- 
centric ridges, which become obsolete over the anal region, where it is nearly smooth ; 
hinge rather narrow, and inner margin crenulated in the middle. 
Length, + an inch; height, 3ths of an inch. 
Localities. Bracklesham and Barton (2dwards); Southampton (J. Sow.). 
This was originally separated from sw/cata by Mr. J. Sowerby, and I have retained it 
as a distinct species. M. Deshayes has given this name as a synonym to Grignonensis ; 
but the shells appear to be specifically distinct. Our present species is more finely ridged ; 
it is shorter and rather more rounded in outline, with the siphonal region less angular. 
A small specimen, which, I think, must belong to this species, has very recently been 
found by Mr. Alfred Bell in the modern deposit at Selsey, called the “ Mud-bed.” This is, 
in all probability, a specimen washed out of the contiguous Eocene Formation. It much 
resembles our present species, more so than any other known to me, but the ridges upon 
the umbonal region are fewer and more distant than on the body of the shell, contrary to 
the general character of the exterior ornament in this genus. 
