two Species of Patelloidea. 115 
retiform appearance at the bottom of the branchial cavity 
was the true organ of respiration ; and that naturalists 
had erroneously considered the foliated cordon sur- 
rounding the body, between the foot and the mantle, to 
be so. Besides. this retiform appearance, «however, 
having been subsequently observed upon several mol- 
lusca, whose respiratory organs are well established, 
the opinion of M. de Blainville is disproved almost be- 
yond debate, by the fact that in the Patelloidee, the 
apparatus existing between the foot and the mantle of 
the Patelle is suppressed, and its place supplied by.an 
undoubted respiratory organ, very differently situated, 
while in other respects - —— is almost pre- 
cisely similar. 
I have long entertained ‘debts whether the shell - 
found on our coast, and commonly known as PATELLA 
amena, Say, did not in truth belong to the Patelloidee, 
and have lately ascertained, from an examination of the 
animal, that such was the case. The position of some of 
the principal organs was found to differ considerably 
from that assigned to them by Quoy and Gaimard, if 
M. Deshayes is correct in his statement that their animal 
was precisely like that of Patella, except in the situation 
of the branchie. I have not access to their own de- 
scriptions. "The anus in the Patella is situated on the 
neck, just back of the head, and the ovarial duct ter- 
minates near the right tentacula, according to those 
authors ; whereas, in our Patelloidea, these organs are 
placed at the bottom of the cervical sac, near the base 
of the branchiz. I have nowhere seen any mention of 
the corneous plate with which the mouth of our species 
is furnished, but have no doubt, from having found it in 
