RISSOA. 



to Alvania, " Operculigerous lobe winged on each side, 

 usually with three caudal cirrhi." Now their type of 

 this genus (R. abyssicola) has but a single caudal fila- 

 ment ; and Barleeia rubra (which, under the name of 

 R. fulva, is comprised in the same genus) has none at 

 all. Of the 16 other species of Alvania enumerated by 

 them, the animal of one only (R. reticulata or Beanii) 

 appears to have been known to them. In their genus 

 Cingula, however, we find R. semistriata, which noto- 

 riously has three caudal filaments, although the charac- 

 ters assigned to that genus are as follows : — " Opercular 

 lobe and caudal cirrhus indistinct or rudimentarv." 

 This last-named genus comprises also Barleeia rubra, 

 var. unifasciata. Under these circumstances it is well 

 that Herr v. Mohrenstern has not absolutely decided on 

 retaining the genus Alvania. I may here observe that 

 the type of Risso's genus Alvania (from Leach's MS.) 

 and 20 others out of the 23 which he described are can- 

 cellated shells, the remaining two being fossil species 

 and erroneously referred to the Turbo interruptus and 

 T. parvus of Montagu. The generic characters given 

 by Risso will apply to almost every convoluted shell with 

 an entire mouth and horny operculum ; and at the most 

 Alvania can only be a synonym of Rissoa. The other 

 genera proposed by Messrs. Adams are in my opinion 

 not more maintainable. Onoba is described as having 

 the whorls not longitudinally ribbed, and the peristome 

 not dilated. In the type (R. striata) both these cha- 

 racters exist to a certain extent. The onlv species as- 

 signed to Ceratia (viz. R. proximo) cannot be distin- 

 guished generically from R. vitrea (placed by Messrs. 

 Adams in Rissoa) or from R. striata. Their genus Setia 

 is characterized as having the tentacles pilose, and 

 the operculigerous lobe destitute of a caudal filament ; 



b 2 



