Vi6 



BULLA Linn. &c. 



Gen. Char. An ovato-globose, convoluted 

 univalved shell; columella none; spire not 

 produced; aperture as long as as the shell ; 

 its external margin sharp. 



In general form the shells of this Genus vary from cy- 

 lindrical to obovate ; they are usually thin, sometimes 

 almost membranaceous, and fragile ; the want of a colu- 

 mella, and the thin edge of the aperture distinguish the 

 species of this Genus as it is now defined by Lamarck, 

 from several that were associated Avith them by Liuneus, 

 such as the Ovulae, &c. and also from the Volvariae. In 

 some species tbere is a thickening of the inner lip of the 

 aperture that much resembles a columella, but this is 

 never plaited ; and such as have it may perhaps hereafter 

 form a distinct Genus. 



The animal to which the shell is attached, is remark- 

 able for having no antennae, and for the foot being 

 laterally expanded so as to be used in the way of fins to 

 swim with ; the mantle does not include the shell. 



BULLA convoluta. 

 TAB. CCCCLXIV.— ^^. 1. 



Spec. Char. Very cylindrical, smooth ; aper- 

 ture linear, expanded a little way from the 

 base; vertex obtuse, perforated. 



Syn. Bulla convoluta Brocchi, p. '211 . tab. 1. 



J^ENGTH two and a half times the width ; the superior 

 extremity is broad, or rather the upper part of the whorls 

 is, as it were truncated, the spire being sunk deeply into 

 its centre. 



Found in Crag, by the Rev. G. R. Leathes. It does 

 not appear to be so strictly cylindrical as required by the 

 description given by Brocchi, but agrees well with his 

 figure. 



