428 



MARINE INVERTEBRATES 



Mytilus edulis, rayed-color variety. 



Mt/tilus edulis is exceedingly abundant along the New England 

 coast. It lives in colonies, often between tides, in pebbly stations 



among large rocks. It is always 

 so fastened by its byssus that the 

 beaks of the valves point down- 

 ward, and the ventral margin pro- 

 jects above the sand or mud. 

 The color of the epidermis in the 

 adult form is black or a deep blue- 

 black; the shell proper is violet. 

 Hinge-teeth are wanting. Length 

 two and a half inches. A variety 

 of this species, M. pellucidus, 

 is often found associated with the typical form. It is brightly rayed in 

 green and yellow. M. edulis occurs in Europe, where it is quite exten- 

 sively used as food. It also occurs (by importation) in San Francisco 

 Bay. 



M. hamatus has a more southern range than has M. edulis, and is 

 found from the Chesapeake southward. Its shell is considerably twisted 

 just below the umbonal region, while its whole surface is densely striated. 

 Its color is dark fuscous. Length one to two inches. It is found in 

 great numbers attached to oysters by its byssus. In Florida it is very 

 common. (Plate LXXVIII.) 



M. californicus. A common west-coast species, which finds its sta- 

 tion among rocks exposed to the surf. It is about the same size as M. 

 edulis, but has a lighter brownish glossy epidermis and several con- 

 spicuous, well-rounded, radiating ribs. The animal is orange-colored. 



Modiola modiolus. After violent storms upon the New England 

 coast, when a large Laminaria is wrenched from its rocky bed and 

 washed ashore, its roots will, in many cases, be found clinging to this 

 large mussel. The thick glossy epidermis of deep chestnut-color folds 

 over the margin of the valves, and the outer surface, especially near the 

 ventral margin, is covered with a tough hairy growth. Length four to 

 five inches. The animal is orange-red. The great size and swelling full- 

 ness of this species at once distinguish it from all others upon our coast. 

 It is not a shallow-water form, 

 but is extremely common upon 

 all beaches north of Hatteras. 

 It also occurs in Alaskan 

 waters to Puget 

 Sound, where it 

 is known as the 

 " great horse- 

 mussel." Some- 

 times these large 

 modiolas maybe 



found in rocky 



tide-pools which ^^^si^T^y 



are washed by the surf at high 



tide. They hide far back in 



the crevices of boulders, and Modwia modulus. 



