182 BRITISH MOLLUSKS. 



1. Assiminea. Animal carrying a pyramidally conical shell, 

 head produced into a ringed muzzle, tentacle and eye-stalk 

 united on each side in one, with the eye at their summit. 

 Operculum horny, composed of a few rapidly enlarging 

 whorls. 



Assinainea G-rayana. (Much enlarged.) 



Genus I. ASSIMINEA, Leach. 



Animal ; body small, carrying a rather solid pyramidally conical 

 shell, head produced into a ringed muzzle, notched in front, 

 tentacles short, united with the eye pedicles, and bearing the 

 eye at their summit, foot ample, broad in front, short and rather 

 obtuse behind, carrying a sUght horny few-whorled operculum. 

 Shell ; pyramidally conical, rather solid, with a minute nearly 

 closed umbilicus, of sis smooth slopingly convex whorls some- 

 what obtusely angled at the base ; aperture with the columellar 

 lip thinly callously reflected. Operculum horny, composed of 

 a few rapidly enlarging whorls. 

 About the banks and inlets of the Thames, in the neighbourhood 

 of Greenwich and Woolwich, where the water commences to be 

 brackish, a small periwinkle exists in profusion, sometimes in the 

 water, but more frequently out of it, under stones, or on the mud, or 

 about the roots of water-flags. The animal partakes of the characters 

 of the marine Littorina, and of a form of By t him a (Hydrobia, 

 Hartmann), in having the horny operculum composed of a few 

 rapidly enlarging whorls ; but it differs from both in the very im- 

 portant feature of having the tentacle and eye-stalk on each side 

 united in one, with the eye at its summit as in the retractile ten- 

 tacle of the Colimacea. A little marine species first discovered by 



