MANGELIA. 449 



body-whorls, anil inferiorly produced into a more or less 

 elongated canal. 



Animal with slender variously formed tentacula, con- 

 verging- at their inner bases, and bearing the eyes at various 

 heights on external bulgings. Siphon produced beyond 

 the canal of the shell ; two branchial plumes. Proboscis 

 retractile, tongue with a simple rachis, and a single series 

 of subulate denticles, arming each lateral membrane. 

 Male organ filiform. Foot ample, truncate in front, 

 variously shaped behind. Operculum usually wanting; 

 when present unguiculated with a terminal nucleus. 



There is so much confusion of nomenclature about those 

 mostly little fusiform British shells, commonly called Pleu- 

 rotomce^ that we are obliged to redefine the genus in which 

 they are here placed. The name MangeUa, as here used, is 

 emj^loyed in the sense in which it would appear it was pro- 

 posed by Leach and adopted by Risso. It is synonymous 

 with Defrancia of Millet. The group differs from Pleuro- 

 ioma proper (with which such of its species as possess 

 opercula have that organ similar) in having a sinuosity of 

 the outer lip at its junction with the body-whorl instead of 

 a true marginal notch below the junction ; and from 

 Clavatula (as redefined by Gray) in having the same 

 difference, and when an operculum is present that organ 

 with an apical instead of a lateral nucleus. We divide 

 the genus into two sections. 1st. Those with an oper- 

 culum, receiving for this division the name Bela, and 

 2nd. Those which have no operculum, or Mangelia proper. 

 These divisions are, however, merely sectional, since, in 

 the first, we find Mangelia turricula and its immediate 

 relatives, forming a very natural little circle, associated 

 with the very dissimilar Mangelia se^it angular is, whose 

 affinities are rather with cosiaia and the allied forms 



VOL. III. 8 M 



