274 PNEUMONOBRANCHIATA. 



These animals live an vegetable matter, like the 

 snails, and are found in damp places on a chalky soil. 



This family contain many foreign, and one British 

 genus. 



Mr. Jeffreys has placed this family in the same 

 group with the Carychiadce Leach (our Auriculidce), 

 overlooking all the peculiarities in the respiratory and 

 sexual organs of the animal. 



Cyclostoma Lam. (Circle Shell.) 



Shell ovate- spiral ; mouth simple, united all round ; 



operculum of a few flat whorls, with a simple 



shelly internal coat ; the foot divided into two 



parts by a longitudinal central groove. (See fig. 



p. 273.) 



The foot is formed of two longitudinal portions : 

 as the animal walks, the portion on one side is first 

 advanced, while the animal holds on by the other ; 

 and then holds on with the advanced portion as the 

 other side is gradually advanced before it. (See 

 p. 273. f.4. Rossmdsler, Icon. i. 89. t. 2. f. 80. 82.) 



This is the case with Cyclostoma lineolata and the 

 exotic species with ovate, few-whorled opercula. 

 The foot of the species with orbicular, horny, many- 

 whorled opercula is not so divided, but broad and 

 expanded, like the foot of other terrestrial Mollusca. 



Dr. Turton, in his descriptions of this genus (ed. 

 1. 93.), says the shell has no epidermis; but this is a 

 mistake : indeed, I am not aware of any shell that is 

 really destitute of this important covering (see Phil. 

 Trans. 1833); though it varies greatly in thickness in 

 different genera ; and in this genus it is very thin, but 

 in some Indian species of the family it is thick, and 



