374 LITTORINID A. Z 
shell of three volutions of the same colour. Mantle simple. 
Head a produced wrinkled muzzle, with a vertically cloven 
yellowish-white disk, armed with the usual jaws, corneous 
plates and tongue. The tentacula are short, flattish, blunt, 
hyaline-white, not setose; eyes large, black, on mere pro- 
minences at the external bases. Foot long, rather thick, 
though narrow, slightly auricled, superficially labiated, and 
tapermg to a moderately elongated rounded termination. 
The operculigerous lobe is much extended, well developed, 
narrow anteally, dilated in a subrotund form posteally, tinged 
with dark smoke-colour at the sides, edges, and on the upper 
surface ; its extremity is of much the same shape as the main 
foot or sole; it does not terminate in a distinct cirrhus; 
indeed, the trace of one is obsolete. On the centre of this 
upper lobe, considerably distant from the end, is fixed a 
suborbicular operculum, that has much the same character of 
the rapidly-increasing paucispiral turns as most of the Rissoe ; 
the under surface of the foot is flake-white ; the upper part 
and neck are marked with irregular, transverse, very fine, 
close-set, pale lead-coloured lines. The animal, therefore, is 
a simple Rissoid of discoidal figure, showing less deviation 
from the type, R. parva, than most of the Rissoe with each 
other. I feel pleasure in having the sanction of Professor 
Forbes to this determination, who observes, in the ‘ British 
Mollusca,’ vol. iii. p. 156, “the Skenee may be said to be 
discoid Rissoe.” 
The animal exhibits the organs freely, as I have remarked 
is the case with all the littoral species, probably from the 
frequent exposure of the branchial plume to the influence of 
free air. This little creature marches rapidly, and is plentiful 
on the finer algz of the pools, at Exmouth, in the half-tidal 
levels. 
It has been objected, that the shell does not show the varix 
at the external lip of the aperture, as in many of the Rissoe. 
This objection is of no value, as many accredited Rissoe have 
not the callus; amongst them, R. fulgida, R. soluta, R. vitrea, 
R. proxima, and others. And as to the foot bemg rounded 
at its posteal extremity, that form is not uncommon in this 
