148 EOCENE MOLLUSCA. 



Shell orbicular, slightly oblique, not very thick ; tumid, heart-shaped, inequilateral ; 

 costatcd, ribs 23 — 26, convex and smooth on the centre of the shell, slightly granular on 

 each side, particularly those in the pedal region. 



JDia meter \ an inch. 



Localities. Bracklesham, Selsey, Brook {JEduoards). 



In Mr. Dixon's work, and also in Mr. Morris's ' Catalogue of Brit. Eo^ssils,' is the name 

 of C. mitis. The specimen from which our figure is taken has likewise the same name in 

 MS., and I have therefore here retained it, although it does not fully accord with the 

 description of the French species of that name. M. Deshayes considered his shell entitled 

 to be separated from C. planicosta (the young of which it much resembles), principally on 

 account of the difference in number of costse, which in mitis are said to be as many as 

 thirty-nine, while in planicosta there are not more than thirty, and this latter number is 

 the full extent of what our shell possesses. Still, I think our British fossil is not the 

 young of planicosta, as it differs in outward form in being more orbicular, more tumid, 

 and less oblique, and the ribs in planicosta are flatter even in the young shell than they 

 are in our present species. In this shell the costse in the pedal region are covered with 

 obtuse tubercles or nodules, and the ribs are not wider than the interspaces. 



11. Caedita obovata, Edwards, MS. Tab. XXII, fig. 13. 



Spec. Char. C. Testa transversa, elongatd, ohlongd vel suhquadrangulari ; valde 

 inaquilaterali, radiatim costatd, costis numerosis depressis, subplanatis ; umbo?iibus obli- 

 quis, depressis ; lunula parvd, cordiformi ; cardine crassiusculo. 



Shell transverse, elongate, oblong or irregularly quadrangular, very inequilateral ; cos- 

 tated ribs numerous, somewhat depressed; lunule small concave, heart-shaped; hinge 

 moderately thick. 



Length, fths of an inch ; height, f ths of an inch. 



Localitg. Bracklesham. 



Two specimens are in Mr. Edwards's cabinet, to which he has given the above name, 

 and I have provisionally adopted the separation he has made. The form of the shell is 

 different from that of any other except carinata, to which it may, perhaps, be referred as a 

 variety ; but our present species has a greater number of ribs (thirty), whereas in carinata 

 there are only twenty-two. In this the costae are not so angular, and they are more 

 nodulous. 



