174 POPULAR CONCHOLOGY. 



They are all small shells, the largest scarcely 

 exceeding an inch in length. Within the 

 mouth, in the last whorl but one, there is a 

 little elastic shelly plate attached to the shell, 

 and called a clausium, from which the genus 

 takes its name. It is used to close up the 

 aperture when the animal has retreated within 

 its shell, and in that respect resembles an oper- 

 culum, or epiphragma; but differs, inasmuch as 

 the latter are either attached to the animal, or 

 are loose and thrown off, whereas the clausium 

 is fixed permanently to the shell. Turton men- 

 tions five or six as natives of England. Many 

 of the species are sinistral. 



44. Bulimus. — Shell oval, turreted, last 

 whorl large ; aperture having the margins dis- 

 united at the upper 

 part, long, not wide; 

 lip thickened and re- 

 flected in the adult; 

 spire obtuse, but much 

 more prominent than 

 in the Helix. Animal 

 like the Helix.-— 135 species recent, and 16 

 fossil. 



