150 EOCENE MOLLUSCA. 
cordatis ; cardine crassiusculo, in valvuld dextrd dente elongato, in valvuld sinistra dentibus 
duobus obliquis. 
Shell roundly trigonal, thick, and slightly convex ; costated, 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. Headon Hill, Roydon (Zdwards). 
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. Carprta pLanicosta, Lamarck. Tab. XXI, fig. 5, a—d. 
Knorr. Petrif., part 2, tab. 23, fig. 5. 1755. 
Seba. Thesaurus, vol. iv, pl. 106, fig. 36, 1765. 
VENERICARDIA PLANICosTA, Lamarck. An, du Mus., t. vii, p. 55; and t. ix, pl. 31, 
fig. 10, 1807. 
—— — J. Sowerby. Min. Conch., t. 1, 1814. 
—_— —_ Desh. Coq. foss. des Env. de Par., t.i, p. 149, pl. 42, 
figs. 1—3. 1824. 
—_— — Bronn. lethzea Geogn., t. xi, p. 946, pl. 38, fig. 
7, 1836. 
CarDITA — Nyst. Coq. foss. de Belg., p. 205, pl. 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, pl. 2, 
figs. 14, 18, 1850. 
var. minor, VENERICARDIA SUESSONIENSIS, D’Archiac. Desc. Geol. du Dep. de l’Aisne, p. 272, 
fide Desh. 
Spec. Char. C. Testa magnd, ovato-obliquatd, cordatd, crassissima, radiatum costatd, 
costis planulatis ; apice acutd incurvatd, aliquando gratulata ; lunuld profundissimda, lata, 
cordata ; margine crenato ; dentibus cardinalibus binis, tenuissimé 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. 
