150 EOCENE MOLLUSCA. 



cordatis ; cardine crassiusculo, in valvuld dextrd dente elongato, in valvuld sinistra dentibus 

 duobits ohliquis. 



Shell roundly trigonal, thick, and slightly convex ; costatecl, ribs few, elevated, and 

 distant ; shell slightly equilateral ; lunule concave ; beaks prominent and oblique ; hinge 

 thick, one tooth in the right valve elongate and oblique, with two in the left valve 

 interlocking. 



Diameter, \ of an inch. 



Locality/. Pleadon Hill, Roy don {Edwards). 



This shell does not appear to be rare. I have referred it to Sandberger's species, 

 depending upon his description and figure. Its principal distinction is a paucity of 

 ribs, not amounting to more than fourteen or fifteen ; these are narrow and distant on 

 the pedal side, with large and flat interspaces between them. The ribs are covered with 

 regularly placed nodules, not imbricated. It is named in Mr. Edwards's cabinet Cardita 

 nodicostata, and considered by him as distinct, in consequence of the ribs being more 

 nodulous or ornamented. 



14. Cardita planicosta, Lamarck. Tab. XXI, fig. 5, a — d. 



Knorr. Petrif., part 2, tab. 23, fig. 5. 1755. 

 Seba. Thesaurus, vol. iv, pi. 106, fig. 36, 1765. 

 Venekicardia PLANICOSTA, ia?Marc/<;. An. du Mus., t. vii, p. 55; and t. ix, pi. 31, 



fig. 10, 1807. 



— — J. Sower by. Min. Conch., t. 1, 1814. 



— — Desk. Coq. foss. des Env. de Par., t. i, p. 149, pi. 42, 



figs. 1—3. 1824. 



— — Bronn. Lethsea Geogn., t. xi, p. 946, pi. 38, fig. 



7, 1836. 

 Cardita — Nyst. Coq. foss. de Belg., p. 205, pi. 17, fig. 1, 1843. 



— — Conrad. Foss. Shells of the Tert. Form, of N. Amer., 



p. 20, t. V, fig. 2, 1832. 



— — J. Sow. In Dixon's Geol. of Suss., pp. 92, 169, pi. 2, 



figs. 14, 18, 1850. 

 var. minor, Venericardia suessoniensis, D'Archiac. Desc. Geol. du Dep. de I'Aisne, p. 272, 



fide Desh. 



Spec. Char. C. Testa magna, ovato-ohUquatd, cordatd, crassissimd, radiatim costatd, 

 costis planulatis ; apice acutd incurvatd, aliquando gratidatd ; lunuld profundissimd, lata, 

 cordatd; vmrgine crenato ; dentibus cardinalibus binis, tenuissime striatis. 



Shell large, obliquely ovate, heart-shaped, very thick ; costated, ribs broad and flat ; 

 umbonal region prominent, sometimes granulated ; lunule deeply impressed, heart-shaped ; 

 margin dentated ; cardinal teeth two, finely striated transversely. 



