184 



mytilidj:. 



upper 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. 



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

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

 violet color ; the epidermis is usually of a dark, shining blue-black. 

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

 gin is a dark violet or blue-black. Under the beaks 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. 



Mniihisi peJIiiridHS, Pennant, Brit. Zool. iv. 2-37, pi. 66, fig. .3— Montagu, Test. Brit. 

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

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

 CiiE.MN. Conch, viii. 84, fisr. 751. — Donovan, Brit. Shells, 81. — Wood, Index, pi. 

 12, fig. 22. — De Kay, N. Y. Moll. 183, pi. 24, fig. 256. — Knorr, Verg. pi. 4, t. 

 15** figs. 1, 2. 



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

 color ; beaks with two or three teeth. 



This beautiful variety has been regarded liy many conchologists, 

 such as those named above, as a distinct species, while others, with 

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

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

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



