Mr. W. Clark on Rissoa pulcherrima. 263 



very black, and fixed at the external angles on minute yellow 

 mamelons. 



Foot long, narrow and rounded in front, with minute auricles, 

 and scarcely labiated; it is a little constricted at the junction 

 with the body ; the sole is impressed with a faint, central, longi- 

 tudinal line, and the posterior termination is sublanceolate. The 

 foot is also furnished with a large operculigerous plate, well alated 

 at the hinder portion, and marked on each side with a dark irre- 

 gular blotch, which often runs into stripes or fine lines at its 

 margins ; indeed, these markings vary, in most individuals, in 

 shape, intensity of colour, and position. The black spot noticed 

 by authors in the Rissoa inconspicua is sometimes, though not 

 frequently, seen in this minute creature, and is often due to the 

 phases of position of the lateral, dark, smoke-coloured patches 

 that are often very apparent on the upper part of the alse of the 

 opercular lobe, which carries a grossly spiral, but finely striated, 

 rissoidean, suboval, corneous operculum ; and its caudal extremity 

 is furnished with a very long, pointed, cirrhal filament, even 

 more developed than in Rissoa parva. 



The animal freely admits of the closest examination, and con- 

 tinues for several days with very little diminution of vivacity. 



The object of this account of the animal of the so-called 

 Rissoa pulcherrima is to propose its removal from the British 

 list as a species^ and to enable malacologists to compare these 

 minutes with the recorded descriptions of what I consider its 

 type — the common and very variable Rissoa inconspicua. 



The agreement of the two appears complete in all essentials ; 

 the minor discrepancies arise from the minuteness of the object; 

 but they yield at once to lenses of high power, which discover 

 the elements of features that sufficiently prove the pulcherrima 

 to be one of the endless varieties of the Rissoa inconspicua. 



In support of these views on the soft parts, see Forbes and 

 Hanley, 'Brit. Moll.^ vol. iii. pp. 113-117; and myself in 

 'Brit. Mar. Test. Moll.' p. 358. 



With regard to the shells I may state, that I have examples of 

 the inconspicua taken by myself at Exmouth, of the same size as 

 the pulcherrima found by Mr. Barlee at Guernsey ; both having 

 the partial spiral lines on the body-volution, and the peculiar 

 and unmistakeable, often semi-obsolete, close-set, vertical ridges 

 or striae. 



These united considerations are, I think, conclusive of the 

 absolute affinity of the two animals. 



I am. Gentlemen, 



Your most obedient Servant, 



William Clark. 



