154 BRITISH MOLLUSKS. 



prevails more towards tlie north ; and was collected by Middendorf 

 in Arctic Siberia. 



Lymn.83a limosa. 



Genus III. "LYWNJEA, Bruguiere. 



Animal; body ovate, carrying a horny shell varying greatly in 

 structure, but mostly ventricosely inflated, mantle reticulated, 

 sometimes capaciously reflected over the shell, foot obtusely 

 attenuated behind, truncate in front, with the margin slightly 

 undulate, head obtuse, furnished with two flat obliquely trian- 

 gular tentacles, with the eyes on obscure tubercles at their 

 inner base. 



Shell ; varying from ventricosely ovate of four whorls to elongately 

 turreted of eight whorls, with the spire proportionally sharply 

 acuminated, yellowish horny, sometimes extremely thin and 

 transparent, smooth or malleated, columella arcuately twisted, 

 lip simple, columellar lip more or less appressly dilated on the 

 body whorl. 



On comparing the Lymncea limosa of our vignette with the Pliysa 

 fontinalis figured at the head of the preceding genus, it will be seen 

 that not only do the shells differ in their manner of convolution, 

 the first-named being coiled to the right, the second to the left, 

 but that there is an important difference in the animal's tentacles. 

 As in Pliysa, the foot of Lymncea is pointed behind, the head is trun- 

 cate and the eyes are similarly placed ; the tentacles are different. 

 Those organs are no longer filiform, or bristle-Eke, but flatly broadly 

 triangular. Along with this difference in the tentacles, there is a 



