784 



EEPORT OF COMMISSIONEE OF FISH AND FISHERIES. 



[6] 



tioued by the wri ter, tlie lower valve of Ostrea may be cemented to it« 

 basis of attachment over its entire outer surface till it has attained a 

 size of two inches in diameter. 



Fig. 2 represents the small spat of which I have just spoken, magnified 

 thirty-two times, and which presents so many peculiarities as compared 



Fig. 2. 



with the adult that it will be desirable to describe it somewhat in de- 

 tail. 



The shell in individuals as small as this up to three-fourths of an inch 

 in diameter is nearly always almost round or oval in outline, and very 

 thin, so as to be easily broken with xiressure by the thumb or finger. 

 In very young ones, like the one figured, the valves are still transpar- 

 ent, but when a little older they become, first, translucent, then 

 opaque, as they acquire increased thickness. In the case of Fig. 2, the 

 shell, which formerly covered the swimming or fr}^ stage, is attached 

 at the hinge ends or beaks of the valves. It measures about gV of an 

 inch in diameter, and shows concentric lines of growth, with apparently 

 well developed beaks, or umbos, which are also doubtless present in 

 the young spat of the European oyster at a late stage, or after fixation. 

 Only the larval shell of the right side is indicated at L in the figure ; 

 it is permanently fixed to that of the spat shell S, but does not present 

 the microscopic characters of the latter. The former appears to be 

 smooth and concentrically laminated, and not altogether structureless ; 

 the latter, under a power of 150 diameters, shows that it is made up of 



