Mr. W. Clark on the Littorinide. 361 
South Devon coasts. I sum up, and conclude the present species 
to be a true Littorina. 
I omit a description of the animal of the very common L. /it- 
toralis, which I reserve as a standard of comparison for my me- 
_m0ir on the animals of the Lacune. 
Littorina littorea, auctorum. 
This exceedingly common, but very curious and interesting 
animal, has not met with the attention it deserves ; we are sure 
that we shall afford gratification in producing a detailed account 
of it. 
Animal spiral ; mantle simple, exactly lining the aperture of 
the shell ; the head is long, cylindrical, not deeply cloven ; mouth 
a vertical fissure, and with the neck and tentacula are marked on 
their upper surfaces on a yellow gronnd, with very close-set dark 
transverse lines, which, with the lead-colour anastomosing lon- 
gitudinal waved markings, give the animal almost a black ap- 
pearance. The tentacula are moderately long, conical, pointed, 
very tumid at their bases, black above, white beneath, on which, 
a little raised, the eyes are set externally. The foot is a very 
singular organ, short, rounded before and behind, scarcely 
auricled, and when in action forms an oblong suboval disk, 
divided by a central sunken line into two longitudinal lobes, 
which, when the animal marches, are each advanced alter- 
nately with an undulating vermicular motion. This curious lon- 
gitudinally divided foot and peculiar locomotion are only to be 
found in one or two other genera; they are particularly conspi- 
cuous in the Phasianella pullus. The under part of the foot is 
yellowish white, bordered by a deep line at a little distance 
within the margin, from which fine transverse ones radiate, 
giving the foot the appearance of being encompassed by a fine 
fringe ; the upper posterior part carries a dark, corneous, suboval 
operculum, with about two turns of elliptical strie, and a very 
excentric nucleus. The buccal apparatus is a deep red fleshy 
mass, supported by two thin coriaceous plates, between which, in 
ordinary-sized animals, a long, at least two inches, riband-like 
white spiny tongue issues, passing down the cesophagus, and be- 
comes closely coiled im the stomach ; its termination is tinged 
with red ; immediately behind the buccal mass is the esophageal 
cordon, which consists of only two white subrotund flattish gan- 
glions, one on each side, and behind them are the salivary glands, 
each formed of a mass of foliaceous granules; there is only one 
branchial plume, of light yellow, attached to the left side of the 
mantle and neck of the animal; the verge is a Jarge flat or- 
gan grooved longitudinally, ridged transversely, dentated on one 
side with two points, one below the other, the lower one with 
