BIVALVIA. 103 



Some Eocene fossils have been figured and described by MM. Nyst, d'Archiac, and 

 Bellardi, under the generic name of Stalagmium, strongly resembling aberrant forms of this 

 genus ; they differ, however, slightly in the dental area, the central portion being much 

 broader than in Limopsis, where the triangular fossette has pushed forward the ligamental 

 connector, so as to diminish materially the dental line beneath the umbo. In those shells 

 called Stalagmium there is an absence of the external triangular fossette, the connector 

 being situated in a linear depression on one side only of the umbo, differing also in that 

 respect from Pectunculus, which it otherwise somewhat resembles ; the ligamental area is 

 ridged or furrowed like most of the shells of this family. If these differences be con- 

 sidered sufficient to constitute generic distinction, those shells must be denominated 

 Stalagmium, Nyst, as the genus proposed by Messrs. Lea and Conrad is untenable for the 

 American Eocene fossil, which, as before stated, is a species of Modiola or Crenella. 



1. Limopsis granulata, Lamarck. Tab. XVII, fig. 10, a, b. 



Pectunculus granul-atus. LamJc. Ann. du Mus., t. vi, p. 117, No. 4, and t. xi, pi. 18, 



fig. 6, a, b. 

 — — Desk. ,Coq. foss. des Env. de Par., t. i, p. 227, pL 35, figs. 4 — 



6, 1829. 

 Limopsis — Prestwich, Geol. Journ., 1847, p. 404. 



— — J. Sow. in Dixon's Geol. of Sussex, pp. 93, 170, t. 3, fig. 19. 



— — Desk. An. sans Vert, du Bass, de Par., t. i, p. 842, 1859. 



Spec. Char. Testa orbiculatd^ lenticulari, convexd-; subcequilaterali ; decussatim 

 striata; striis longitudinalibus angustioribus granulosis ; cardine recto, umbonibus minimis ; 

 marginibus obsolete crenulatis. 



Shell orbicularly lenticular, convex, slightly inequilateral, striated or radiated and 

 decussated ; radiations fine and granular ; hinge straight, umbones small, depressed ; 

 margins obsoletely or irregularly crenulated. 



Diameter, ^ an inch. 



Localities. Bracklesham {Edwards). 



France : Grignon, Parnes, Senlis [Deshayei). 



This is a rare species in England, and found only at the above locality ; it is said to 

 be abundant in the Paris Basin. 



The surface of this shell is covered with fine, small, radiating striae, which are crossed 

 or decussated by prominent lines of growth ; the conjunction of these two lines causes an 

 elevation, thus giving a granular surface to the exterior; the shell is nearly lenticular and 

 equilateral, the diameter being, as near as possible, the same in each direction, though 

 occasionally it is a trifle in excess in the height. The hinge is furnished with three to 

 five denticles on one side of the umbo, nearly vertical, and on the other from five to six in 

 a curving direction, and the interior margin is faintly and somewhat irregularly denticulated. 



