106 
THE PEARL OYSTER 
" Sketches of the Natural History of Ceylon, executed from 
" drawings made for the official inspector exhibiting the 
*' ascertained size of the pearl oyster at every period of 
"its growth from the ' spat ' to the mature shell." And 
with a well-drawn plate by Sowerhy issued under such 
authority it is not surprising that eminent naturaKsts fol- 
lowing accepted without hesitation that the minute shell in 
question was the spat of the pearl oyster. Captain Phipps, 
Superintendent of Pearl Fisheries at Tuticorin, had however 
his doubts, and expressed and maintained them in the face 
of the long list of high authority to the contrary. He was 
good enough to show me these minute shells, and there is no 
doubt they are the shell of Avicula vexilhim (Eeeve,) a shell 
that in maturity attains only one quarter of an inch in 
length. The largest shell that I have ever seen out of several 
hundreds, if not thousands, measured || of an inch. Natu- 
ralists were further confirmed in considering these minute 
shells to be spat of the pearl oyster by observing that their 
shell exhibited under the microscope the same prismatic 
cellular structure as the shell of the pearl oyster. But we 
have the authority of Carpenter for that cellular structure 
being common to most of the Aviculw. 
These minute shells of Avicula vexillum which have so 
longbeen taken for the spat of our pearl ojsteT,Avic/(/(i fiicafa , 
may be seen side by side with A. facata in the British Museum 
at South Kensington, and in the Government Central 
Museum at Madras. Closely examined side by side it will 
be observable that A. rexiUnm is very much more convex than 
A. fucata ; is more oblique ; has the ear on the sinal or short 
side not produced in an almost straight line, but rounded 
off ; has the right valve fitting deeply into the left valve, 
whereas in A. fucata the two valves lie ver}- neaidy flat against 
each other. Avicula vcxilluii) has again not a trace of the 
numerous spatulated spines with which the young of A. fncnra 
is always covered in regular cii'cles, and it has distinctly 
