354 



I have no hesitation in consigning this species to the genus 

 Rissoa. It differs in many points from the true Littorince, 

 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 Rissoa, being 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 Littorinae, which I believe 

 never swim ; the Rissoce in general are oftener seen floating 

 in a reversed position than otherwise. 



The shells of this section of the Rissote are subject to great 

 variety from locality, varying in the number and in the inflation 

 of the volutions, and in 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 ulvce. 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. ulva 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 minute wings ; these 



