RISSOA. , 369 



August 14, 1854. 



I have just taken another lively example of this species, 

 and I need only remark, that the peculiar gait above men- 

 tioned was less apparent than in the animal already described ; 

 I am therefore inclined to consider it of that nature which 

 may be observed in the Rissoce, when in creeping they arrive 

 at the level of the water, and commence exserting and retract- 

 ing with rapidity the buccal apparatus. 



In the animal just discovered the curious tails of the foot 

 were well developed, the angle of separation being about that 

 of the fore and middle finger of the hand when placed as far 

 apart as possible. In all the animals which I have observed I 

 never met with a similar termination of the main foot. 



R. VITREA, Montagu. 

 R. vitrea, Brit. Moll. iii. p. 125, pi. /5. f. 5, 6, and iv. p. 264. 



The animal occupies a pale yellow essentially smooth shell, 

 of 4J tumid, though less rounded and more taper volutions, 

 with shallower sutures than in the R. proximo,. The general 

 colour of the animal is very pale dirty- white. The mantle does 

 not protrude beyond the aperture. The head or rostrum is sub- 

 cylindrical, double the length of that of the ' proximo,,' invested 

 with a tunic to near its extremity, grooved above, emarginate 

 at the end, forming two minute, flat, symmetrical, arcuated, 

 terminal lobes, vertically cloven beneath as in R. parva ; the 

 colour on both surfaces is a moderately suffused pink, through 

 which the buccal apparatus is visible; and when the neck 

 is much exserted it appears coloured with pale pink hues. 

 The tentacula are flat, much longer than in the ' proximo,,' 

 but not clavate like it at the tips ; they have however the 

 same fine, sharp setae at the extremities ; the eyes are at the 

 centre of the bases of the tentacula, not raised, nor half the 

 size of those of its congener. The foot is truncate in front, 

 very slightly labiated, with unusually short obtuse auricles ; 

 not bifurcated posteriorly, but has an entire, somewhat taper 

 and rounded termination, not extending beyond the second 

 volution : the operculum is fixed on a simple lobe, scarcely 

 distinguishable from the upper part of the foot ; it is rather 



2 B 



