340 LITTORINID A. 
conchologically appear to be Rissow, inhabit only the coralline 
zones, and as most of the animals are unknown, the true rela- 
tions between the animals of the littoral and coralline districts 
are not as yet satisfactorily ascertained. 
Littorina has only four species, L. littorea, L. rudis, L. neri- 
toides, and L. littoralis. 
LITTORINA, Férussac. 
L. tirrorea, Linneeus. 
L. littorea, Brit. Moll. ui. p. 29, pl. 83. f. 7,8 5 (animal) pl. G.G. f. 3. 
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 
marked on their upper surfaces, on a yellow ground, with very 
close-set, dark transverse lines, which, with the lead-coloured, 
anastomosing, longitudinal waved markings, give the animal 
almost a black appearance. The tentacula are moderately 
long, conical, pointed, very tumid at their bases, black above, 
white beneath, on which the eyes, a little raised, are set ex- 
ternally. The foot is a very singular organ, short, rounded 
before and behind, scarcely auricled, and when in action 
forming an oblong suboval disk, divided by a central sunken 
line into two longitudinal lobes, which, when the animal 
marches, are each advanced alternately with an undulating 
vermicular motion. This curious longitudinally-divided foot 
and peculiar locomotion are only to be found in one or two 
other genera ; they are particularly conspicuous in the Phasia- 
nella 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 frmge; the upper 
posterior part carries a dark, corneous, suboval operculum, 
with about two turns of elliptical striz, and a very excentric 
