46 PECTINIDA. 
PECTEN, Bruguiere. 
* Shell firm, solid, of a porcellanous texture. 
P. opercunaris, Linneus. 
P. opercularis, Brit. Moll. ii. p. 299, pl. 50. f. 3, pl. 51. f. 5, 6, and 
pl. 53. £27. 
Animal suborbicular, thick, lentiform; this shape results 
from the support given to the organs by the powerful central 
circular adductor muscles ; the colours are very variable, white, 
pink, fawn, orange and brown; the body, with the amalga- 
mated ovarium, is a compound of flake-white meandering 
lines, spots and blotches, and its conical termination is of the 
palest vermilion to the intenser hues of that colour; it de- 
scends from the dorsal to the ventral range, on the anterior 
side of the great subcentral muscle. The mantle is thin, 
except at the fleshy margins, and open throughout, with the 
exception of a short dorsal area; there is not a trace of 
siphons; it would be too large for the shell if it were not 
doubled on itself and fixed a little within the duplicature to 
the shell by very slender muscular pallial threads. At the 
folding a cord-like margin springs, but the true mantellar 
margin floats loose, and is considerably within this line; both 
are furnished with 2-3 rows of irregularly deposited, conical, 
white, pointed cirrhi of three different lengths; those of the 
inner circle are tinged with brown; the outer or fixed range 
has the longest filaments, and in addition 35-40 subglobose 
ocelli that have pearl-coloured pupils with black circles ; 
these vary im size, and extend at equidistances throughout the 
peripherial range to the auricles. 
The foot springs from the body just below the palpi; it is 
yellowish white, subcylindrical, of small volume, deeply cloven 
or furrowed, and scoop-shape at the termination ; it appears 
to have no locomotive use, and only to be the vehicle for pro- 
ducing a byssus for occasional fixation, especially of the young 
animal. I have seen most of the species thus fixed. 
There are a pair of subcircular branchiz on each side, vary- 
ing in different dividuals to all shades of the colours above 
