302 GINGLYMACONCHA, VENERIDZ. 
teeth : the umbones are very much recarved, and are situated 
behind the middle of the shells. 
1. CRASSINA BRITANNICA. 
Shells rather convex, concentrically grooved; the grooves 
equidistant ; the epidermis deep or pale chestnut, olive or yel- 
lowish-olive. Length one inch and three-eighths ; height one 
inch. 
Var. a. Valvarum margines interné denticulatz. 
Venus Danmonia, Mont. Test. Brit. Suppl. 45. t. xxix. f. 4; 
Flem. Edinb. Encycl. vii. 96; Dill. Desc. Cat. 167. 
Venus sulcata, Mont. Test. Brit. 131; M. & R. Trans. Innn. 
Soc. vil. 81. t. u. f. 2; Turt. Conch. Dict. 235. 
Var. 8. Valvarum margines interné tenuiter elevate, at non 
denticulate. 
Venus Scotica, M. §& R. Trans. Linn. Soc. viii. 81. t. u. f. 3; 
Mont. Test. Brit. Suppl.44; Flem. Edinb. Encycl. vii. 96 ; 
Turt. Conch. Dict. 236. 
Var. a. The margins of the valves internally denticulated. 
Var. 6. The margins of the valves internally elevated, forming 
a slightly elevated rim ; but are not denticulated. 
This species is by no means uncommon on the south and 
western coasts of Devon, and on the northern coasts of ireland 
and Scotland in deep water with a sandy bottom. 
From the vast number of specimens in the collection of the 
British Museum, collected by Colonel Montagu, C. Prideaux, 
Esq., Mr. J. Cranch, Mr. Clealand and myself, I have not the 
least reason to doubt that they are mere incidental varieties ; 
the rim occupies in Var. /3. the same part exactly as the den- 
ticulations in Var. a. 
Genus 45. CHIONE. 
Cytherea ** Lamarck. 
Shells subcordate, equilateral; the hinge of the right valve 
has four teeth, three of them converging and approximating 
at their bases ; the other is solitary, situated a little remote from 
