3(3 



the attached surface. But on the extensive flats at the 

 upper ends of Nanoose Bav and of Oyster Harbor they 

 occur free on the surface by thousands and more or less 

 covered with barnacles. 



Good specimens reach two inches in length by an inch 

 and a half in breadth, with a straight dorsal mar-in and 

 a semicircular ventral curvature. The right, upper or 

 smaller valve is nearly flat or but little convex and fits 

 into the margins of the larger, convex, lower or left valve, 

 the greater part of the lower and posterior margin being- 

 scalloped, while the left valve has corresponding ridges 

 and points. The color is usually dark (those under 

 stones lighter) with the older parts weathered grayish 

 and the umbonal region of the left valve is often attached 

 to a small stone or another oyster or bears a scar. In- 

 ternally the shell is extensively pigmented, dark, with 

 smaller bands or blotches of lighter pearl, while the 

 muscle scar is rather lighter and banded. The mantle is 

 broadly margined with dark, which may also creep up 

 on to the abdomen. 



The most interesting feature in connection with the 

 Pacific oyster of Canada is its divergence in some re- 

 spects from the mode of breeding of our Atlantic species. 

 In the British Columbia form there is no primary sepa- 

 ration of individuals into males and females— the sexes 

 are united in each individual. In other words each in- 

 dividual is bisexual, monoecious or hermaphrodite. In 

 this respect it is identical with the English or common 

 European species {Ostrea edulis L.). 



My first observations were made on July 12, on 

 specimens procured under stones near the Biological 

 Station. Nearly all appeared to be males, and, as they 

 were of small size, I took it that, as commonly occurs, 

 the males had ripened earliest. But one was of medium 

 size and contained eggs that at once attracted my atten- 

 tion on account of their large size, opacity and rare ex- 

 hibition of nucleus. Measured exactly as all my former 

 measurements, these gave: Oc. V, obj. 2 = 6.5; Oc. V, 



