DESCRIPTION. 171 



PLATE XXV. 



Sections of the several genera are here offered 

 rather as subjects of curiosity than as necessary to 

 the science. They, however, show more accu- 

 rately the true form of the inner chamber than even 

 the aperture itself, which is often altered by the 

 expansion or contraction of the margin, and is 

 generally oblique to the direction of the whorls. 

 The sections of Nautilus and Turbo constitute the 

 two explanatory figures at the top of Plate I. 



PLATE XXVI. 



Fig. 1. Helix acutangula. 



Shell imperforate, thin, pellucid, acutely cari- 

 nate ; spire slightly convex ; aperture ovato-lan- 

 ceolate. 



Nondescript. 



Specimen pale horn-colour, finely striate longi- 

 tudinally, whorls three, nearly flat at top ; 

 extremely brittle. 



Habitat unknown. 



This and the following shell, as well as the three 



