218 PYRAMIDELLID^. 



roundod, pillar-lip without folds, base often perforated. 

 All operculum. 



Animal (according to Loven) with slender cylindrical 

 tentacula, which are slightly swollen at their tips, and 

 have approximated bases, near the outer sides of which 

 the eyes are immersed ; the mouth is furnished with a 

 long retractile proboscis ; the tongue is probably unarme<l ; 

 the foot is linguiform, truncate in front, where it is sur- 

 mounted and preceded by produced mentum ; the opercu- 

 ligerous lobe is ample, developed more on the right side, 

 where it is three or four plicated, than on the left, where it 

 forms a single rounded lobe. 



This genus was founded by Loven for a shell which 

 appears to be congeneric, if not identical, with the Turbo 

 ascaris of British authors. As yet the animal has been 

 met with by the Swedish naturalist only, and his account 

 of it places the type without doubt in the immediate 

 neighbourhood of Eidima. With it we have associated a 

 small group of shells which have been variously placed in 

 other genera, usually in Chemnitsia, but which have the 

 ovate or rounded mouth and tumid volutions characteristic 

 of the shell of AcUs. Mr. Searles Wood has used the 

 name Alvania, proposed by Leach, for this genus ; but 

 judging from Mr. Gray's " List of Genera," the synonomy 

 of Alvania is doubtful, and certainly, as used by Risso, it 

 became but another term for Rissoa. We prefer accord- 

 ingly adopting the clearly defined and well-founded genus 

 proposed by Loven. 



The genus Mesalia, of Gray, has close relations with 

 Aclis, but its true position and value can hardly be made 

 out at present. 



