100 CARDIADZ. 
This species is taken abundantly at Exmouth, of all sizes, 
in the coralline zone. 
C. epuLE, Linneus. 
C. edule, Brit. Moll. u. p. 15, pl. 32. f. 1-4; (animal) pl. N. f. 5. 
Animal suborbicular ; the body is large, subglobose, and of 
an opake white; mantle pale yellow, edge fringed. The 
siphonal apparatus forms two short conical tubes, separate 
from their bases, and divergent; the branchial has ten long 
white cirrhi, with two or three intermediate shorter ones 
springing from the orifice, which is encircled by a dark or 
red-brown line; the anal tube has a similar line, but no 
cirrhi; itis provided with a retractile tubular valve ; both tubes 
have on their surfaces the usual characteristic curly white 
filaments, and they vary from whitish to pale yellow or red- 
dish-brown. The foot is considerably smaller than in any of 
the other Cardia, and has very little of the long cylindrical 
aspect of that organ in its congeners, being rather flat and 
lanceolate ; its colour varies from opake white to pale brown 
or yellow. There are a pair of moderate-sized, pale brown, 
suboval branchize on each side, finely pectinated, the upper 
one being much the smallest ; the palpi are red-brown, longish, 
pointed, flat, and subtriangular, smooth on the outside and 
pectinated within. 
There are many varieties of this common species which 
result from habitat; they are sometimes excessively thin, 
arising in certain estuaries from a more than usual affusion of 
fresh with the salt water, and under those conditions have 
been named by some naturalists C. rusticum. It is proper to 
observe, that the true Linnzan C. rusticum is a very different 
species, which has long been known to collectors, though 
misnamed C. tuberculatum, the strongest and most ponderous 
of all the Cardia. The young of one of the varieties, from its 
umbonal transverse bands, has been mistaken for our C. fas- 
ciatum, the C. elongatum of some authors, but the oblique out- 
line of the latter species will always distinguish it from any of 
the young fasciated varieties of C. edule. 
