* 
150 MOLLUSCA FROM THE CRAG. 
1. Hippacus vERTIcorRDtvs, S. Wood, Tab. XII, fig. 18, a, 4. 
Cryeropon? verticorp1a. SS. Wood. Catalogue, 1840. 
VERTICORDIA CARDIIFORMIS. SS. Wood. MS., 1844. 
a —_ J. Sowerby. Min. Conch., t. 639, 1844. 
Hrppacus acuricostatus. PAil. En. Moll. Sic., vol. ii, p- 42, t. 14, fig. 19, 1844. 
Spec. Char. Testa suborbiculari vel cordiformi, converd, subequilaterali, tenui, costatda 
costis circa 16 tncurvatis, compressis, radiantibus, rugosis ; apicibus antrorsim involutis ; 
margine denticulato. 
Shell suborbicular, or heart-shaped convex, thin, subequilateral, costated, ribs about 
16, incurved, radiating, compressed, rugose; apices involute; margin denticulated. 
Diameter, 3ths of an inch. 
Locality. Coralline Crag, Sutton. 
This elegant shell is by no means abundant as a British fossil, and from the figure 
and description above referred to, there is every reason to believe the same species 
once inhabited the seas which deposited the Upper Tertiaries of Calabria. A slight 
difference exists between our shells, as far as can be determined without an inspection 
of the specimens, but such as does not appear to be more than a local variation, and 
not sufficient to affect their specific identity. 
The Italian fossil has given to it only 13 ribs, while there are 15 to 16 in our shell, 
but like some species in the genus Cardiwm (which it resembles externally,) this may 
be a variable character: the ribs are elevated, and laterally compressed, rounded on 
the top, but not sharp or angular, as Philippi’s name would seem to imply, and as his 
figure represents; they are elegantly curved, and are generally rugose, or coarsely 
imbricated, and distributed at about equal distances; the concave spaces between them 
are rather wider than the ribs themselves, and appear to be finely granulated, or studded 
over with small papilla. In the interior are the marks of two somewhat large 
adductor muscles, the anterior one is the more deeply impressed, that by the mantle 
is indistinct: the ligament or cartilage appears to have been placed so far within the 
dorsal margin of the shell, that when the valves were closed it was probably not visible, 
being placed in a depression beneath the margin, extending into a cylindrically formed 
aperture towards the umbo, and the receding of the ligament, or its desertion on the 
anterior side, causes a slight involution of the umbones, like that of Jsocardia, though 
in a very minor degree. A callous, but prominent and obtuse tooth in the right ~ 
valve, close to the umbo, fits into a sinus in the left valve: the shell is beautifully 
nacreous within, and though not particularly thin, the ribs are visibly marked in the 
interior by deep indentations, and they project considerably beyond the margin, inter- 
ocking and serving the office of prominent denticles. 
