122 INVERTEBRATA OF MASSACHUSETTS. 



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 \vhite and silvery in the 

 centre, but all the margin is a dark-violet or blue-black. Under 

 the beaks are about four thin, oblique denticulations, quite distinct 

 when the overlapping epidermis is removed. Length QTG inches, 

 height ly 3 !? inch, breadth 1 inch. 



Variety pellucidus. Shell smooth, thin, transparent, radiated 

 with blue and horn-color ; beaks with two or three teeth. 



My'tilus pellucidus, PENNANT ; Brit. Zool, iv. 237, pi. 66, f. 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, f. 1. CHEMN. ; Conch , viii. 84, f. 751. DONOVAN ; Brit. Shells, 81. WOOD ; 

 Index, pi. 12, f. 22. 



This beautiful variety has been regarded by many concholo- 

 gists, 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. edulis. None of the 

 specific marks given to it seem to be constant. Radiations ap- 

 pear in the solid old shell, as well as in the thin ones ; and, on 

 the other hand, the thin ones are often without radiations. Tur- 

 ton thinks it may always be distinguished "by having only two or 

 three tuburcular teeth under the beaks." But this does not ac- 

 cord with my observations. 



The shell is subject to many distortions from accident, and from the 

 form of the bodies on which it grows, or of cavities in which it be- 

 comes wedged. Hence, probably, arises that curved form which 

 takes the name of M. incurvatus. 



This Mussel is one of the most common and best known of all our 

 shells. It is very extensively distributed throughout all northern seas. 

 It is abundant on the coasts of England, France, Norway, and Russia, 

 where it is extensively used as food, as its name imports, and also for 

 manure. In this country it has, as yet, been put to no economical 

 use, though I am assured by a friend of acknowledged good taste, that 

 when cooked it is more palatable than the common clam. Unlike 

 the Modlola modiolus, it appears to inhabit shallow waters, in positions 

 where it is left uncovered at the recess of the tide. It attaches itself 

 by its byssus to rocks and timbers, and may be thus seen under 



