RISSOA. 135 



ness of all early figures of the smaller objects of natural 

 history, and the meagre descriptions which formerly suf- 

 ficed to distinguish the few known members of a genus 

 from their nearest congeners. The delineation of the 

 American P. Michaudii in the " Galerie de Douai" (vol. i. 

 pi. 26, f. S, 4), harmonizes very fairly with the general 

 look and peculiar aperture of our species, but the whorls 

 scarcely appear so rounded, and the spire is somewhat 

 shorter. 



The shape is abbreviated ovate-conic, and the surface, 

 when freed from the extraneous coating of dirt, with 

 which it is generally found enveloped, is smooth and 

 shining; the substance is thin, semitranspareut, and of a 

 greyish or tawny olive colour. The five volutions of which 

 it is composed, are more or less shouldered or subscalari- 

 form, being horizontally compressed, and often suban- 

 gulated above ; below, they swell out suddenly from the 

 strongly pronounced suture, yet are not particularly tumid 

 in the middle. The whorls of the spire, which quickly 

 tapers to a small and moderately pointed apex, are short, 

 and of quick enlargement in breadth, but of rather slow 

 longitudinal increase ; the dorsal length of the penult turn 

 is, in general, much less than the half of its breadth. The 

 body is always at least as long as the spire, and often fills 

 three-fifths of the entire length ; it is quite as broad, or 

 even broader than it is long, and is moderately convex and 

 gradual in its basal declination. The extreme base is 

 narrow, for the outline of that side of the final whorl which 

 is opposite to the lip at first sweeps very obliquely in- 

 wards, and then, by its comparative straightness, foi-ms 

 an angle with the previous arch. The mouth, which 

 is somewhat obliquely ovate, and projects at the base, 

 occupies fully two-fifths of the entire length ; it is much 



