102 

 CHAPTER XXV. 



OF THE BULLA. GENUS XXIl. 



BULLA. 



" Animal a Limax. Shell univalve, convolute, unarmed ; the aperture 

 somewhat compressed, oblong, longitudinal, very entire at the base ; 

 pillar oblique, smooth." — Lixn. 



The description of the aperture here is rather vague ; what 

 the essential character of this genus is seems very difficult, if 

 not impossible, to determine ; and, if we examine the shells 

 called Bulled by Linnaeus, the forms of the apertures are so 

 various that we must conclude no essential character can be 

 drawn from that part any more than from the pillar, which in 

 many other shells is oblique also, as in all the Cyprcece, many 

 VolutcE, &c. &c. By the term pillar Linnaeus means the inner 

 edge or axis which iims through the centre of the shell, from 

 the point of the spire to the opposite point or end. 



Linnaeus himself seems not to have clearly determined in liis 

 own mind what should be a Bulla and what should not ; for 

 several species which he had in his former publications ar- 

 ranged under other genera he has in his twelfth edition of 

 Bystema Naturce placed among the Bullce, as B. Ficus, Rapa, 

 and virginea (/. 64 and 66) : he also expresses some doubts of 

 some other species, as B. Terebellum and achatina. 



The species placed together under this genus are certainly 



