62 INVERTEBRATA OF MASSACHUSETTS. 



Saxicava distorta, SAY ; Journ. AcaA. Nat. Sc., ii. 318. 

 My'tilus rugosus, LIN., &c. 



Shell oblong-oval, coarse, white, very irregular in shape ; in- 

 equivalve, the right valve projecting over the left except at the 

 shorter end ; inequilateral, the anterior side rounded and generally 

 of about one half the length of the other side, but the beaks are 

 sometimes nearly terminal ; the posterior end is most frequently 

 truncated, but at other times rounded ; gaping ; beaks rather 

 prominent, from which two ridges or elevated lines run back- 

 wards, one near the margin, and the other to the lower angle, giv- 

 ing the included surface a lozenge shape. In some shells these 

 lines are very distinct, and they are armed with a series of 

 elevated, arched scales or spines ; the basal margin is usually con- 

 tracted at the middle, and slightly arched upwards ; surface coarse- 

 ly marked with the lines of growth, and irregularly undulated ; 

 epidermis thin, dingy-yellow. Ligament aided by the mantle, 

 which adheres all along the back. Teeth for the most part want- 

 ing ; when not wanting, a single rudimentary tooth in one valve is 

 received into a pit in the opposite valve ; muscular impressions 

 obscure. Length 1 inch, height f inch, breadth f inch. 



Found adhering to marine objects. They may almost always 

 be found among the roots of fuci, which are thrown up by storms, 

 adhering to stones, shells, &c. The best I have ever obtained 

 were taken from a log drawn out of one of our timber docks, to 

 which they were adhering by a silken byssus issuing from the 

 middle of the base. 



The foot of the animal is of a bright orange-color. 



This shell is a perfect Proteus, of which no description can be given 

 that is not liable to mislead. I think there can be little doubt, that the 

 same shell exists on the European shores, and that it has been already 

 described under at least one name. But, as I have not the means of 

 arriving at certainty on this point, I have chosen, until better satisfied, 

 and as it will introduce no new name, to retain that which Mr. Say 

 applied to it. 



In the first place, it would come under the genus BYSSOMY A, on ac- 

 count of its being furnished with a byssus. But the majority of the 

 best modern conchologists regard this circumstance as of little im- 

 portance, and consequently reject the genus. Some specimens cor- 



