JEFFREYSIA. 153 



noticed as R. alhella at the Cork Meeting of the British 

 Association, — by which designation it is enumerated in JNlr. 

 Thompson's vakiable list of Irish Invertebrata (Report Brit. 

 Assoc. 1843) — was identical with the glahra of Brown's 

 " Illustrations." 



The shell is extremely thin, diaphanous, quite smooth, 

 of an uniform lustrous snowy white, and of an oblong-conic 

 shape. There are only four to four and a half volutions, 

 the posterior one of which is dome-shaped. The body, 

 whose basal declination is much rounded and rather quick, 

 only occupies from two-fifths to three-sevenths of the dorsal 

 length, but viewed from below is equal to the spire ; the 

 latter is moderately attenuated, yet rather broadh^ rounded 

 at its apex. The suture is fine and a little oblique, but 

 the whorls being decidedly ventricose, are well defined ; 

 they are moderately high, that is to say are half as long 

 as broad. From three to four are visible above the mouth ; 

 their longitudinal increase is moderate, the penult not 

 being disproj)ortionately larger than the preceding turn. 

 The aperture occupies two-fifths, or rather more, of the 

 total length : it is of a somewhat ovate figure, slightly 

 contracted above, and well rounded below, where it is 

 produced a little beyond the basal level ; the throat is 

 quite smooth. The peristome is continuous, but owing 

 to the thinness of the shelly matter, is not distinctly so. 

 The outer lip is acute, simply arcuated, and moderately- 

 projecting ; it has no tendency to expand. The inner lip 

 is very narrow, erect, slightly reflected and sinuated, being 

 more oblique above and somewhat perpendicularly sub- 

 arcuated below ; behind it exists a slight subumbilical 

 chink, which is much more apparent in the immature 

 examples. The operculum is very thin and pale ; its 

 nucleus is lateral, and near the pillar. The length of 



VOL. III. X 



