CYCLOSTOMA. 



queiitly the lip is thickened when full grown only, and 

 there are none of those varices ornamenting the outer 

 surface, which add so much to the beauty of the Scalaria.* 

 The Delphinulae (which are nearly related to Trochus and 

 Turbo) are of a very different texture, being perlaceous 

 within, they are moreover of a comparatively thick sub- 

 stance and the lip is not reflected when full grown. The 

 Paludinae and Valvatae which are related to Ampullaria, 

 approach more nearly to Cyclostoma than the Scalaria or 

 the Delphinulae do, though independently of the great 

 difference in the form of their opercula and their aper- 

 tures ; these also may be known from the greater number 

 of Cyclostomata by their not having a reflected lip when 

 full grown. 



The Cyclostomata have been very properly separated 

 from the Linnean Genus Turbo, and the Genus as thus 

 established has been adopted by Lamarck and subsequent 

 authors ; I have included in it all land shells having the 

 following characters. Shell turbinated, thin, mostly with 

 an obtuse apex to the spire, and with rounded whorls : 

 aperture nearly circular, peritreme more or less angular 

 at the upper part, sometimes a little thickened, generally 

 reflected and fringed externally. Operculum horny, in- 

 clining to testaceous in some species, spiral. 



All the Cyclostomata are land-shells, and most of them 

 are tropical ; one or two only are found in Britain, and 

 very few others are Europsean. The animal of one spe- 

 cies alone, the C. elegans, is known in this country, it is 

 ably described by the Rev. M. J. Berkeley, in the Zoolo- 

 gical Journal, vol. IV. p. 278, to which I refer. The Genus 

 appears to be very nearly related to Helicina, though 

 differing materially in the form of the aperture and in the 

 operculum. One species, namely, the C. Turbo, ap- 

 proaches so nearly in form to the Helicina, that, not 

 having seen its operculum, I cannot be quite sure that I 

 have placed it properly in Cyelostoma. 



The shells of this Genus mostly belong to the southern 

 hemisphere, over which the various species are spread in 

 every direction : the Europsean species are very few and 

 small, while several fine species are found in the East 



* The Scalariae approach very nearly to the Turritellae. _ 



