24 



DESCRIPTIONS OF THE EDIBLE BIVALVES OF CALIFORNIA 



NATIVE OYSTER 

 Ostrea lurida Carpenter 



The irregular, attached shells of the small native oyster are familiar 

 to all. It occurs throughout the region treated in bays or lagoons that 

 olfer places for attachment, though in many localities the numbers are 

 small. It seems nowhere to be used as extensively as it deserves. In 

 Tomales Bay it is at present cultivated and investigations looking 

 toward the further development of the industry are under w^ay. For 

 this reason no extensive treatment is here attempted. 



The Eastern oyster (Ostrea virginimm) is raised in large amounts 

 in San Francisco and Tomales bays from imported spat, but the species 

 has never established itself on this coast. 



SCALLOP 



Pcctcn circuldiis Sowerby 

 Plate 1, figures 1 and 2 



Other names — Pecten; fan shell. 



Description — This bivalve may readily be recognized by the lateral 

 projections on either side of the umbo, not present in any other form 

 here treated, the well marked radiating ribs and grooves ending in 

 points which alternate and interlock with those of the opposite valve. 

 There is only one muscle (the posterior adductor) for closing the shell, 

 l)ut this is yery large and well developed. Other scallops not greatly 

 different in general appearance may be met with, of which P. diegensis 

 may be mentioned. It differs in having the two valves unlike, one 

 being nearly flat and the other markedly arched. 



Habitat and habits — There are several species of scallops. This 

 is the largest of those found in shallow water (except diegensis). It is 

 very active, contrasting with the bivalves as Vi^e usually know them. 

 At low tide it may he found lying on its right side on the sand left 

 dry by the receding tide in bays or lagoons ; it does not burrow, though 

 sometimes the smaller specimens may be found fastened to a rock or 

 dead shell by means of a byssus, like that of the mussel. But it is 

 not completely at the mercy of the tides for it can swim about actively. 

 This it does by clapping the valves of its shell together and forcing out 

 the water between them in a sharp stream, the direction of which it 

 can regulate by means of the mantle. When the shells are opened 

 folds of the mantle e:xtend in from either margin to meet and close 

 off the interior. When the shell is shut the contained water is forced 

 out where the mantle eds^e is least stiff and, as a result, the pecten will 

 shoot off in the opposite direction. According to Kellogg* in the 

 case of the Eastern forms the jet is forced out first next to one "ear" 

 and then the other. If an animal is placed wrong side up in shallow 

 water it will promptly right itself, and often at low tide it may be 



♦Shellfish Industries 1910, p. 336. 



