RIVER-SIDE SPECIES. 29 



Another kind of Zonites, namely, alliarius, with a 

 darker and more solid shell, has a very strong smell 

 of garlic (hence the specific name), especially when 

 irritated. This peculiar smell, however, varies in 

 intensity, and is sometimes hardly perceptible, even 

 when the animal has been much provoked. A third 

 species, nitiduliLs (with a variety nitens), is not un- 

 common on the banks of the Thames near London, 

 preferring more watery places than the last named 

 (PL II., fig. 4). It has been met with also at Cam- 

 berwell and Hammersmith. In similar situations 

 occurs Z. nitidus, a variety of which, named albida, 

 has been found among the rejectamenta of the Thames 

 at Richmond. Dr. Gray has obtained Z. crystallinus 

 at Battersea. It is a thin, glossy, and transparent 

 shell, of a greenish-white colour and glassy appear- 

 ance, and the animal inhabiting it is of a clear 

 greyish- white colour, and nearly transparent. Another 

 species of Zonites (Z. glaber) has lately been found 

 in Hertfordshire, and some other parts of England. 

 It somewhat resembles Z. alliarius, but is much 

 longer, and has more convex or swollen whorls. 



The minute shells of the genus Pupa are not very 

 readily seen ; and were it not for the fact that the 



