a 



Centimeters 



FiGDRE 4. — C. virginica. 



Wellfleet Harbor, Mass. Dimensions: height 9.5 cm., length 8 cm. 

 (b) inside of upper (right) valve. 



(a) lower (left) valve; 



valve. Interior surface white, often with faint 

 purpHsh stain over the muscle scar or near the 

 edges. Large promyal chamber on the right side. 

 Edges of the mantle deeply pigmented. Non- 

 incubatory, discharging a very large number of 

 eggs and sperm directly into the water. Intro- 

 duced from Japan into the waters of British 

 Columbia, western states of the United States, 

 and Alaska (Ketchikan). Small number of speci- 

 mens of C. gigas were at various times planted in 

 Mobile Bay, Ala., and in Barnstable Bay, Mass. 



Highly variable. Typical C. gigas is a long, 

 straplike oyster. The form C. laperousi (con- 

 sidered by Japanese malacologists as a separate 

 species) has round, highly ridged shells. 



C. commercialis (Iredale and Roughley), Sydney 

 rock oyster, commercial oyster. This Australian 

 species (fig. 7) was imported to Hawaii about 

 1925-28 and planted along the shores of the 

 western end of Kaneohe Bay, in Oalm Island. In 

 1930 several of the imported specimens were ex- 

 amined by the author and found to be ripe and 

 spawning. During World War II the small popu- 

 lation of this species was destroyed by dredging 

 operations. 



Valves markedly unequal and variable. The 

 left valve deep and cup-shaped, recessed under the 

 hinge, slightly fluted; the edge weakly crenulated. 

 The upper valve flattened. Inner side of valves 

 chalky white, frequently with bluish or creamy 

 markings on the upper valve; muscle scar usually 

 not pigmented. Edges of valves with small denti- 

 cles extending about half way around the valve. 

 Sexes are separate; nonincubatory. 



Usually grows to 3 to 4 inches in height, but 

 cultivated specimens have been reported to reach 

 10-inch size. Normal range of distribution New 

 South Wales and Queensland; frequently found 

 in the intertidal zone attached to rocks, sticks, 

 and shells. 



C. rimdaris Gould (fig. 8). This Japanese 

 species has been planted in waters of Puget Sound 

 with the shipments of seed of C. gigas. In Japan 

 tlie oyster is known as "suminoegaki" (Hirase, 

 1930). 



The shell orbicular; strong and large, adult 

 specimens reaching 6 inches in height. Left, 

 lower, valve slightly concave, upper valve shorter 

 and flat. The left valve with generally indistinct 

 lamellae of pale pink color with radiating striae. 

 The lamellae of the right valve are thin and al- 



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FISH AND WILDLIFE SERVICE 



