378 LITTORINIDZ. 
Rissoe without that appendage ; indeed, if we were to look for 
strict typical specialties im either the hard or soft parts of any 
mollusk, every species must become a genus. 
Shell—Of eight yellowish-white, rounded, finely reticu- 
lated volutions with oblique well-marked sutural lines. The 
apex is obtuse and not reflexed, as stated by me in another 
place: I was deceived by imperfect specimens, which led 
me into the error of supposing that it would prove a 
Chemnitzia. é 
This is one of the slenderest British shells, having only an 
axial admeasurement of ;4,, and a diameter of ~; uncie; the 
outer lip is thin, and the aperture is oblong-oval and almost 
entire. 
Animal.—The general colour is hyaline-white, shot through- 
out all its organs with a mixture of very minute close-set 
points, short lmes or blotches, of flaky and frosted snow- 
colour. Mantle even with the shell, except that at the aper- 
tural upper angle it emits the filament I have so often men- 
tioned as being present in all the Rissoe, and whose particular 
function is doubtful. The muzzle is slender and rather long, 
having the first half from the neck, on its upper part, clothed 
with a very close tunic or tight overlay; the disk is smooth, 
compressed, bevelled to a fine edge, and almost circular, with 
a median vertical fissure on the under surface, m which I have 
often seen the delicate white corneous plates, jaws, and lingual 
riband ; but great powers and much time are required to seize 
a favourable opportunity of vision in so minute and restless a 
being. The tentacula are very like those of Rissoa striata, 
moderately long, flat, rounded or obtuse at the tips, quite 
smooth even under high powers, divergent, with large black 
eyes, not on pedicles or prominences, but fixed on the centre 
of their bases with very little external imclination, and widely 
apart; there is no connecting tentacular veil, nor the least 
triangularity, foldmgs, or the presence of apical inflations, as 
in the Chemnitzie ; on the march the eyes are usually carried 
within the margin of the shell. The foot is slender, greatly 
hollowed out in front and deeply labiated, with distinct, long, 
arcuated linear auricles which play on the march, or, as 
