360 Mr. W. Clark on the Littorinide. 
Littorina, Férussac. 
Littorina neritoides, Linneeus. 
Turbo petreus, Montagu et aliorum. 
Animal spiral ; mantle even with the shell; the head is a long 
proboscidiform cloven muzzle, the upper part of an intense black 
cloud-colour ; orifice of the mouth white with a vertical fissure ; 
tentacula awl-shaped, moderately long, flattened ; eyes large, not 
on pedicles, but placed on the substance of the skin at the bases 
of the tentacula, inclining externally only in a trifling degree. 
The buccal mass is plain brown, supported by two thin coriaceous 
plates of the same colour, from whence a very long white spiny 
tongue proceeds to the stomach, and there hes coiled as in Lit- 
torina littorea ; but it is proportionately longer than in that spe- 
cies, being 2 inches long. Foot nearly as in L. littorea, very 
slightly auricled and curved in front, rounded posteriorly to a 
terminus, which is a little jagged or dentated, forming an oval 
when not in action, but on the march a very elongated oval ; 
above its colour is black ; underneath a pale lead ground mixed 
with two shades of white and one of purple. These colours are 
divided into three portions ; the anterior one is the narrowest, of 
an intense hyaline white, the middle is also hyaline, and the third 
is hyaline pale purple. The foot is not strictly divided into two 
longitudinal half-parts as in L. hittorea, but at the anterior part, 
where the intense hyaline white terminates, appears transversely 
broken or furrowed, so as to allow of a subdued alternate undu- 
latory gait, or quality of progression, something like that of L. 
littorea, in which the whole of the longitudinal half is first ad- 
vanced, and then the other; but here only half of the auterior 
part of the foot is moved forward, and then the other, and so on, 
dragging the other part in alternate times. 
This alternate action of parts of the foot is a very smgular 
character, which obtains, more or less, in all the true Littorine, 
and is with very few exceptions confined to that genus. There is 
only one branchial plume, and the internal and external organs 
are nearly those of L. lidtorea. The sexes are distinct in all the 
Pectinibranchiata. I ought to have mentioned the suboval cor- 
neous dark operculum, pointed superiorly with about two rapidly 
increasing gyrations, the nucleus being at the basal end. 
This species is one of those that inhabit the highest levels of 
the littoral zone, and often dwells for an indefinite time far be- 
yond even the spray of the sea. It appears a mystery how the 
branchize are kept moist; I suspect the minute saline particles 
earried by the winds suffice, especially as the long exposure to 
atmospheric influences has almost rendered the branchie of pul- 
moniferous quality. They clothe the rocks in myriads on the 
