150 MOLLUSCA FROM THE CRAG. 



1. HIPPAGUS VERTICORDIUS, S. Wood, Tab. XII, fig. 18, a, b. 

 CRYPTODON? VERTICORDIA. 8. Wood. Catalogue, 1840. 

 VERTICORDIA CARDIIFORMIS. S. Wood. MS., 1844. 



J. Sowerby. Min. Conch., t. 639, 1844. 

 HIPPAGUS ACUTicosTATUs. Phil. En. Moll. Sic., vol. ii, p. 42, t. 14, fig. 19, 1844. 



Spec. Char. Testa suborbiculari vel cordiformi, convexd, subtequilaterali, tenui, costatd 

 costis circa 1 6 incurvatis, compressis, radiantibus, rugosis ; apicibus antrorsum involutis ; 

 margine denticulate. 



Shell suborbicular, or heart-shaped convex, thin, subequilateral, costated, ribs about 

 1 6, incurved, radiating, compressed, rugose; apices involute; margin denticulated. 



Diameter, -fths 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 Cardium (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 papillae. 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 Isocardia, 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. 



