two Species of Patelloidea. "— c 
some one in our Society will take up the i and 
give it a full i investigation. 
PATELLOIDEA ALVEUS. 
Synonyms. Patélla alveus, an Jour. Acad. 
Nat. Sciences, VI., 267, tab. 2, f. 20. 
. Patelloidea frei Cournovy. 
OssrnvarroNs. There is hardly any perceptible 
difference between the animal of this species and the pre- 
ceding, except. that in consequence of the lateral com- 
pression of the shell, its body is rather more oblong, and 
the back a little more convex. The tentacula also, ap- 
pear to be somewhat longer and more slender than in 
P: amena. The position of the eyes is the same in 
both, as is that of the genital and anal orifices and 
branchie, the latter seeming merely a trifle broader. 
Perhaps it would be more correct to consider it as a 
constant variety of P. amena, than as a distinct species. 
It is, however, very marked and unvarying in its external- 
characters ; and many species have been received as 
valid, upon far narrower distinctions than exist be- 
tween this and Mr. Say's shell. It may be added, that 
I have never found P. álveus except upon marine plants ; 
whereas P. amena is for the most part met with upon 
rocks exposed to the sea. 
