262 Mr. W. Clark on Rissoa pulcherrima. 



those species in which the spores do not ripen until late in the 

 autumn, the germination does not take place until the following 

 spring, and occurs therefore at a time when none of the previous 

 year's spermatozoids remain and no new ones are yet developed. 



[To be continued.] 



XXIV. — On Rissoa pulcherrima. By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



Norfolk Crescent, Bath, 14th Sept. 1857. 

 Gentlemen, 



My friend Mr. Barlee, to whom all that are interested in 

 malacological pursuits are under the greatest obligations, has 

 just favoured me, from Guernsey, with many lively specimens 

 of the Rissoa pulcherrima of recent authors, which has been 

 constituted a species, solely, I believe, from conchological indices. 

 I have therefore thought that some of your readers would be 

 glad to have an account of the external organs of this, if it be 

 so, undescribed animal. 



Rissoa pulcherrima, Forbes and Hanley. 



Shell spiral, ovately conical, pale yellowish-white, of 3J-4J 

 well-rounded volutions divided by a rather deep suture, and 

 marked with 2-4 rows of distinct, palish rufous spots, which 

 in other words are lines running from base to point, that are 

 variously interrupted, so as to form well-separated, subquadrate, 

 minute areas. The aperture is suboval, usually thin at the 

 outer margin, with little or no umbilical fissure. Axis -ij^-i^i 

 diameter ^j--^j of an inch. 



Animal. — Ground-colour white, shot with the minutest snowy 

 flakes and points, and blotched with dark smoke patches and 

 lines, as well as with more or less yellow or sulphur- coloured 

 suffusions on particular parts of the body. Mantle entire ; but 

 I did not detect the pendent filament from the aperture, which 

 I have often mentioned as visible in the Rissoce, and which is 

 perhaps the generative organ. 



Rostrum moderately long, above longitudinally cloven or bi- 

 lobed ; buccal disk below having the usual vertical fissure, from 

 which the animal frequently protrudes the white corneous jaws 

 and masticatory processes ; it is tinged with yellow hues, above 

 and below, of various intensity and extent. 



The tentacula are long, slender and flat, rounded at the tips, 

 and horizontally clothed with fine setse; the eyes are large. 



