376 LITTOEINID^E. 



suffused with lemon-yellow, and studded with distinct flake- 

 white points ; there is very little trace of a depressed medial 

 line on the sole. 



A subcircular, paucispiral, corneous operculum, with a sub- 

 central nucleus, is fixed on an alated, very elongated upper 

 lobe, narrow anteally, dilating behind, marked with minute 

 smoke-coloured blotches at the sides and edges, as in Rissoa, 

 and with more intensity on the upper surface. The operculum 

 is placed on a circular dilatation at the centre of the lobe, 

 which is produced considerably beyond it to a blunt, though 

 lanceolate-shaped point, which laps on the upper surface of 

 the posterior part of the foot, at some distance from its termi- 

 nation, and appears to be the locum tenens of the typical 

 E/issoid cirrhus, though it is not what is understood as strictly 

 cirrhal. These sort of pedal filamentary appendages are of 

 no generic value, and from the uncertainty of their presence 

 in many of the Rissoce, of scarcely specific importance. 



This species is perhaps the commonest that exists; it is 

 most abundant on the lower littoral levels; the animal is 

 omnivorous, feeding on animal matters, and on Alga and 

 Corallina officinalis; it is equally plentiful in the deepest sea 

 districts ; its variations in figure are endless ; every locality 

 has its variety. The animal is as free as the typical Rissoa 

 in showing its organs. 



These notes show that this so-called Cerithiwn, in organic 

 structure, is a perfect Rissoa. Even the shell, as in that genus, 

 has the characteristic varix at the outer lip, and in the pauses 

 of growth, similar varices declare that the aperture is always, 

 when the animal is not on the increase, provided with the 

 typical callous pad. 



We conclude by observing, that if the R. parva be consi- 

 dered .the type of the genus, and it be not at hand, the 

 R. planorbis, or this species, malacologically, has greater and 

 more appropriate claims to act as a vice-type than any other 

 Rissoa in the list. We cannot comprehend how three genera 

 can with propriety be constituted from essentially identical 

 animals. 



We think that the Murex adversus of Montagu- a Ceri- 



