— 26 — 



ROCK OYSTERS 



Aiiomia peruviana d'Orbigny 



Plate 3, figure 3 



Monia inacroschisnia Deshayes 



Plate 3, figures 1 and 2 



Description — These two species are similar enough to be treated 

 together. They may be recognized by the more or less irregular form 

 which, like the oyster, comes from their permanent attachment, though 

 in this case the shell itself is not fastened to the rock. A strong 

 muscular byssus passes through a deep notch in the right valve to 

 fasten to the support. t 



Habitat and habits — Attached to stones between or below tides. 



Use — The rock oysters are not, as far as known, used for food, 

 thoug'h edible. 



Distribution — Monia is found from Alaska into Lower California; 

 Anomia southward from San Pedro (Dall). Shells are common along 

 the beaches but because of their relative unimportance no special 

 search was made for living specimens. 



SEA MUSSEL 



Mytilus calif ornianus Conrad 



Plate 4, figures 1 and 2 



Description — This nuissel reaches a large size, sometimes measur- 

 ing more than eight inches. The valves are covered with a black 

 glossy periostracum, which is usually worn away in the older parts of 

 the shell. The surface is marked with concentric growth lines and 

 faint radiating ribs but both vary greatly in different specimens. 



Habitat and Habits — Tlie sea mussel is found attached to the rocks 

 of exposed reefs and headlands in dense "beds" extending from near 

 high tide line to the level of the lowest ebbs. They do not flourish in 

 quiet waters but reach their largest size where exposed to the full 

 force of the surf of the open ocean. Here they lie closely crowded 

 together and so firmly anchored by the tough threads of the byssus to 

 the rock and to each other that the breaking of the waves fails to 

 dislodge them. 



Use — The sea mussel is an excellent food mollusk and properly 

 prepared, as for instance by steaming, is not surpassed in flavor by any 

 of our bivalves. Since they are widely distributed and very abundant 

 they deserve an even greater use than is at present made of them. In 

 their preparation particular care should be observed to follow the 

 general rules laid down for selecting bivalves (see page 68). They 

 should be sorted and only those capable of closing their shells promptly 

 should be used. The exposure to sun and air of those at the higher 

 levels often injures them and cases of poisoning have resulted from 

 their use. All such danger, however, may be avoided by the simple 

 precaution of gathering at low tide only those covered at other stages 

 of the water. 



