90 
THE PEARL OYSTER 
Not to lose the researches of our predecessors it may- 
be well here to mention that Dr. Kelaart and many other 
naturalists have written valuable contributions, referring to 
it under the name Meleagrina margaritifera. The error of 
referring the chief of pearl bearers to the name margaritifera 
was a natural one, but I have the authority of Mr. Edgar A. 
Smith, Conchologist of the British Museum_, for terming the 
animal with which we have to do Avicula {meleagrina) fucata, 
and it is so named in the British Museum cases. 
Having thus come to a definite understanding about the 
animal we are discussing I may mention that, as the term 
"spat" is somewhat laxly used popularly to cover the whole 
young state of the oyster, I apply it only to the stage in 
which, after having passed from ova to the swimming larval 
form, it is precipitated to the bottom and becomes spat in 
my limited sense. 
The Exterior. 
It is well to note the chief features of the shell of the 
pearl oyster, both to distinguish it from the edible oyster, 
and to know it, when less than a quarter of an inch broad, 
from a shell that has been mistaken for oyster spat. In the 
edible oyster the hinge point is an angular prominence called 
the beak or umbo, and the inequivalved and approximately 
oval-shell falls from it at right angles, one valve or side of 
the shell being flat and thin, the other valve thick and highly 
convex. The pearl oyster has the same beak, or umlo, the 
embryonic shell of bivalves, but it is prolonged by ears into 
a straight hinge from which the nearly equivalved shell 
falls obliquely, the length or height of the hinge being very 
nearly the same as the breadth of the shell taken rect- 
angularly from the hinge to the furthest point of contour. 
Below the shorter ear is a notch, which is the byssal sinus ; 
both valves are slightly convex, and nearly equally so, and 
both are of about the same thickness. In the edible oyster 
