354 LITTORINID &. 
I have no hesitation in consigning this species to the genus 
Rissoa. It differs in many points from the true Littorine, 
especially in having the foot short, truncate, auricled in front, 
and rounding to an obtuse point behind; the under surface is 
not subdivided as in L. Littorea. It has not the entire aspect of 
the foot of the Rissoe, bemg without the posterior filamentary 
appendage of the operculigerous lobe of the type; and in its 
progression has not a trace of the oscillatory action so conspi- 
cuous in the foot of the typical Littorine, which I believe 
never swim; the Rissoe in general are oftener seen floating 
in a reversed position than otherwise. 
The shells of this section of the Rissoe are subject to great 
variety from locality, varying in the number and in the inflation 
of the volutions, and im colour from pale brown or yellowish- 
white to dark red-brown or horn-colour. I think that one of 
the light varieties with the tumid volutions is Montagu’s 
Turbo subumbilicatus, which species appears to be in great 
obscurity. Having carefully examined the animals of all the 
varieties, I can decidedly state that they are identical with 
the typical Rissoa ulve. I am much inclined to think that 
the Rissoa Barleei is one of the varieties. 
Having repeated the examination of two of the varieties of 
the R. ulve found at Exmouth, the one having a pale horn- 
coloured shell with flat volutions, the other tumid and red- 
brown, with the animal rather larger and of a darker lead- 
colour than the former, I am enabled to state, that I cannot 
discover the slightest organic difference between the two, and 
their action and habitudes are identical. The variation arises 
from habitat ; the one, the pale variety, is found lurking under 
stones, the other exposed in the open patches of the green 
oozes of the estuary. The shells are so different in aspect, that 
the conchologist would pronounce them distinct, but the mala- 
cologist steps in, and offers a practical example of the superi- 
ority of his determinations, by showing the two to be identical. 
Both the varieties have the under part of the foot aspersed with 
sulphur-yellow, opake, minute flakes. The operculigerous lobe 
is ample, and extends a little on each side, beyond the pedal 
disk, or forms what, by some, are called mmute wings; these 
