142 EOCENE MOLLUSCA. 



present very considerable variation in regard to magnitude. C. planicosta measures 

 5 inches in diameter, while C. atomus is, according to M. Deshayes, only 1 millimetre in 

 diameter ; but they all possess considerable solidity. 



1 . Caedita actjticostata ? Lamarch. Tab. XXII, fig. 5, a, h. 



Venericakdia acuticostata (?), LamarcJc. An. du Mus., t. vii, p. 57, No. 4, 1807. 

 — — Desk. Coq. foss. des En v. de Par., t. i, p. 153, pi. 25, 



figs. 7, 8, 1825. 

 Caedita — Nyst. Coq. foss. de Belg., p. 208, pi. 16, fig. 6 ? 1843. 



— — /. Sow. In Dixon's Geol. of Sussex, p. 92, 1850. 



— — Desk. An. sans Vert, du Bass. dePar., t. i, p. 760, 1858. 

 Cakdium seeeigerum, Lamarck. An. sans Vert., t. vi, p. 19, No. 8, fide Desh., 1819. 



Spec. Char. " C. Testa subrotundd, tumidd, cordiformiy subobliqud, crebricostatd, 

 costis angustis, angulatis, squamoso-serratis, anticis di/pUcatis." {Deshages) 



Shell suborbicular, tumid, heart-shaped, slightly oblique, costated ; ribs narrow, angu- 

 lated with squamose tubercles. 



Diameter, fths of an inch. 



Locality. Bracklesham {Edwards). 



Erance : Chaumont, Grignon, Parnes, Courtagnon {Deshayes). 



Belgium : Aeltre, pres de Bruges {Nyst). 



Asia Minor, sec. Deshayes : Egypt, fide Bellardi. 



M. Deshayes, as above referred to, speaks of this species as a British fossil, but as 

 difi'ering from the French shell in the number of costge. He observes, " Dans I'espece 

 d'Angleterre ces cotes sont au nombre de vingt seuleraent ; on en compte trente, quelque- 

 fois trente deux dans Y acuticostata." Our shell has 24 to 26 costse, and appears to 

 correspond better with the Belgian fossil of that name, which is said to have 26. The 

 costse upon our specimens are more or less imbricated all over, but especially so on those 

 in the pedal region. The ribs have a central keel, and there is a faint ray on each side, 

 dividing the rib, as it were, into four parts, two on each side of the central keel. This 

 appears to differ from C. carinata of 'Min. Conch.' in being less elongated, and in the ribs 

 being more regularly nodulous. 



Fig. 11, Tab. XXII, represents a specimen from Bramshaw; it has on the tablet 

 the MS. name of C. asperrima. It is intermediate between acuticostata and carinata, 

 but is not, I think, sufficiently distinct to form a species of itself, but an abnormal form, 

 and for the present it is placed as a var. — C. acuticostata, var. asperrima. 



