TRIBE NYMPHACEA. 87 
under an olive epidermis, internally violet; dorsal margin sloping 
posteriorly, witha rounded off acumination, anteriorly sub-truncated ; 
ventral edge posteriorly rounded; anteriorly slightly flexuous : 
umbones blackish. 14,..343;.—Peru and C. America. 
C. TruncuLus.—Donax. T. Lam. 24.—Philip. p. 36.—Ch. 
J. 253, 4.—Born. t, 4. f. 3. 4.—Knorr. 1. t. 7. f. 7-H. t. 262. 
J. 1.—Polt. 1. t. 19. f. 12, 3. Oblong wedge-shaped, thick, only 
marked with obsolete minute longitudinal striez, posterior side 
nearly thrice as long as the obliquely truncated anterior ; posterior 
dorsal edge sub-rectilinear: a linear excavated lunule; yellow, 
(rarely lilac) often with paler radiating lines, and one or two violet 
bands ; inside usually violet. 2..11.—Mediterrancan. 
CRASSINA. 
Sub-orbicular, transverse, equivalve, sub-inequilateral, close ; hinge 
mith two strong, diverging, primary teeth in the right valve, and 
two unequal ones on the other ; ligament external, on the longer 
side. 
C. Suncara.* Turt. B. p. 132. t. 11. f. 1, 2.—Venus. S. 
Mont. p. 131.—Lam. 27.—C. Danmoniensis. Lam. 1.— 
Venus. D. Mont. sup. t. 29. f. 4.—D. p. 167.—Bl. t. 75. f. 7. 
—W.t.7. f. 21. Roundish, triangular, and slightly compressed, 
white under a dark brown cuticle, with smooth strong regular equi- 
distant concentric ridges ; beaks nearly central and inclining ; lozenge 
lanceolate lunule nearly heart-shaped: imner margin glossy and 
crenulated. 1 ..14.—Hngland2 
C. Fusea.. Desh.—Teiuina. F. Poli. 1. t. 15. f. 32, 3. 
Solid, triangular, somewhat heart-shaped, brown, sub-equilateral, 
with twelve or thirteen very regular large transverse grooves: lunule 
impressed deep and smooth : white within and the margins toothed. 
Mediterranean. 
C. Scorrca.* Mont. sup. p. 44.—Venus8. Lam. 55.—D. p. 
167.—Lin, Tr. 8.t. 2. f.3.—Turt. B. t. 11. f. 3, 4.—W. t. 7. f. 
20. Ovate, heart shaped, with strong regular flattened concentric 
smooth ridges, white, with a brown cuticle, and the margin entire. 
1.—Scotland, England. 

2 The shell which has been considered by American authors as 
identical with the European speciesis most assuredly distinct. We 
propose for it the name of C. Larisuuca. Cordiform, convex, 
thick, heavy, with about eleven much elevated concentric ribs, 
which are much narrower than the interstitial grooves; cuticle 
black; umbones eroded ; lunule ovate oblong, and as well as the 
lanceolate lozenge, excavated. 1..14.—N. America. 
