III'LIX. 151 



In the treatment of the species I have generally followed Jules 

 Mabille, whose paper, "Materiaux pour une fauna malacoloyique des 

 iles Canaries" is the most recent and complete publication on the 

 subject. A number of descriptions have been taken from Mousson, 

 and from Wollaston. 



H. PLICARIA Lamarck, 1816. PL 49, figs. 51, 52. 



Imperforate, depressed, solid, opaque, corneous brown, lighter 

 below, unicolored, or with very obscure darker bands above, about 

 three in number, and sometimes a fourth just below the periphery ; 

 obliquely costate with elevated separated coarse ribs ; frequently 

 split or slightly interrupted upon the periphery, and which are 

 crenulated by very numerous dense fine spiral impressed lines, which 

 scarcely or not at all cut the surface between the ribs ; whorls 4, 

 moderately convex, regularly increasing, the apex nearly smooth, 

 large, obtuse, first two whorls much smoother than balance of shell, 

 body-whorl obtusely subangular at its beginning, becoming rounded 

 and rather tumid and gibbous below as it approaches its termination, 

 abruptly, deeply deflexed and deeply constricted behind the aper- 

 ture ; aperture very oblique, contracted, small, irregularly oval; 

 peristome white, very broadly, flatly expanded, its terminations some- 

 what converging, joined by a thin callus; basal margin thickened 

 within by a slightly tortuous lamellar denticle, appressed over the 

 umbilical region, which is but slightly or not at all indented. 



Diam. 22, alt. 14 mill. 



Ins. Teneriffe, Canaries. 



H. plicatula Lam., H. orbiculata Wood, H. planorbula Gray are 

 synonymous. Some authors have included several allied forms under 

 the name plicaria, but attention to the above diagnosis will enable 

 any one to separate them. The sculpture of the ribs is very charac- 

 teristic. 



H. BENTHENCOURTIANA Shuttleworth, 1853. PI. 50, figs. 60, 61. 



In form and appearance similar to H. plicaria, but distinguished 

 by the thin shell, narrow (often subobsolete) bands, regularly spaced 

 incremental costre, which are less developed than in plicaria, and 

 without the secondary sculpture of incised lines shown by that spe- 

 cies ; the interspaces between costre are finely striate; the young 

 shell is pilose. 



Ins. Teneriffe, Canaries. 



