of Littorina Angulifera, 345 
by its turbinated form, composed of a mass of viscera contained 
in a sac and the branchial cavity ; the other (2), placed below 
the former, the foot, surmounted, in front, by the head. 
Upon examining the animal more closely, we find, protrud- 
ing from the head, two non-retractile tentacula (3), at the 
outer part of the base of each of which, placed upon a small 
prominence, is the eye (4). Between the tentacula, the head 
is elongated into a sort of rostrum (5), at the extremity of 
Which is the mouth. On the right side of the head, in the 
male, projects a body (6), terminated by a disk or sucker (7), 
probably useful in retaining a hold of the female during pro- 
creation ; from its posterior face protrudes the penis (8), which 
is capable of elongation. During repose, the penis is bent 
back against the side of the visceral sac, within the branchial 
cavity, 
The foot. itself (9) has the same general appearance and 
Composition as in all Gasteropoda. It is excavated, above, 
for the reception of several viscera; has a large retractor 
muscle (10), which originates from the columella of the shell, 
mserted into it; and has, placed upon its upper part behind, 
an operculum (11). 
Upon the lower whorl of the turbinated mass of the animal, 
on the outside. of the visceral mass, and extending as far back 
% the second whorl, is placed the branchial cavity. Its 
entrance, situated just above the head, is a large opening, ex- 
tending from side to side, and corresponds with the orifice of 
the shell of the animal, when the foot and head are extended. 
branchia (12) is stretched into a membranous expanse 
ming the outer wall of the cavity ; its anterior, thickened 
edge is the collar (13); and it is laterally attached to the 
Sutside of the junction formed by the visceral sac with the 
margin of the excavation of the foot. A distinct branchia 
does not Project from one side of the branchial chamber, as is 
ai in other pectinibranchiate gasteropods, but the outer 
Wall of the cavity has a branchial arrangement on its internal 
vi 
OL, v. 93 
