184 



MYTILID^. 



ui)per or posterior margin by a somewhat abrupt curve ; this margin 

 takes a direction parallel to the base, for a short distance, and then 

 the two unite by a regular curve ; an abrupt ridge passes from the 

 beaks to the lower and hinder angle, above which the shell gradu- 

 ally slopes to a sharp edge, and below which it bends so abruptly 



Fig. 483. 



j1/. edulis. 



as to present a broad, flattened space, in the centre of which is a 

 slight fissure for the passage of a byssus. The sliell itself is of a 

 violet color ; the epidermis is usually of a dark, shining blue-l)lack. 

 Within, the shell is white and silvery in the centre, but all the mar- 

 gin is a dark violet or l)lue-l)lack. Under the l)eaks are about four 

 thin, oblique denticulations, quite distinct when the overlapping epi- 

 dermis is removed. Length, two and four tenths inches ; height, 

 one and three tenths inches; breadth, one inch. 



Var. pellucidus. 



3fi/fi!ti.<! pellucidus, Pennant, Brit. Zool. iv. a"??, pi. 66, fig. 3 — Montagu, Test. Brit. 

 160. — Maton and Rackett, Lin. Trans, viii. 107. — Dillwyn, Catal. 310. — 

 TuKTON, Conch. Diet. 110; Lin. Syst. iv. 292; Brit. Biv. 197, pi. 15, fiji;. 1.— 

 Chkmn. Conch, viii. 84, fisr- 7,51. — Donovan, Brit. Shells, 81. — Wood, Index, pi. 

 12, ftff. 22. — Dk Kav, N. Y. Moll. 183, pi. 24, tig. 256. — Knork, Vcrg. pi. 4, t. 

 15**, tigs. 1, 2. 



Shell smooth, tliin, transparent, radiated with blue and horn- 

 color ; beaks with two or three teeth. 



This l)cautiful variety has been regarded l»y many conchologists, 

 such as those named al)0ve, as a distinct species, Avhile others, with 

 more apparent propriety, consider it as a variety, depending chiefly 

 on age, of the true M. cdvlis. None of the specific marks given to 

 it seem to be constant. Radiations appear in the solid old shell, as 



