MUEEX. 493 



all the organs with intense- white flakes, mixed nearly equally 

 with pink lines, points and blotches ; these are minute, though 

 varying in size and irregularly distributed. Mantle rather 

 thick, not extending beyond the margin of the aperture, 

 except the branchial fold, which is often carried considerably 

 beyond the canal of the shell ; it also forms in the outer lip, 

 at the upper part, a small, open, slightly produced conduit 

 that lines a deep scission in that part of the shell. This spe- 

 cies is one of the most typical of the Pleurotomata of British 

 authors, but its distinguishing feature, the sinus, is not suffi- 

 ciently stable in the British species to give them the impress 

 of generic distinction. 



The head is a short red protrusion, vertically cloven, evolving 

 a long proboscis ; it contains the usual short spiny tongue and 

 other organs of the buccal apparatus ; consequently in this spe- 

 cies the tentacula do not completely coalesce basally. The want 

 of conjunction of the tentacula at their bases is the character 

 principally relied on by those malacologists who contend for 

 a generic distinction between the so-called Fusus and Pleu- 

 rotoma ; but this character as regards the British Pleuro- 

 tomata is very variable and cannot be depended on, as 

 some decided ones have not a trace of an exserted head or 

 veil, and have their tentacula conjunctive at the bases, with 

 only the separation of the proboscidal fissure; and in the 

 genus Fusus the same discrepancies occur, as in some of the 

 minor species the tentacula coalesce, whilst in others the con- 

 junction is slightly intercepted by the scarcely appreciable 

 appearance of a head or head-veil. The tentacula in the 

 present animal are short, with eyes on the external extre- 

 mities of offsets which extend within a very short distance of 

 their points. The foot at rest is beautifully puckered ; when 

 in action it is truncate in front, with small auricles, flat, long, 

 acuminated behind, and extending to the fourth volution from 

 the base. There is not a trace of operculum : it is difficult to 

 account for the absence of this appendage ; it may be surmised 

 that the apertures of these shells are so narrow as not to 

 require such a protection, but this argument cannot be relied 

 on, as we see that the Aporrhdis pes pelecani has a corneous 



