124 Mr. W. Clark on the Muricidse. 



ter. The mantle is simple^ being only produced into a simple 

 bi'anchial duplicature lining the canal of the shell, and as in its 

 congeners is often extended beyond it. The head is very short, 

 flat, forming a sort of head-veil, under which the usually armed 

 pi'oboscis issues ; consequently the tcntacula do not form a com- 

 pletely conjunctive angle at their bases. 



I should have been glad to have seized and admitted such a 

 character as generic in default of a better to separate the Pleu- 

 rotoma and Fusus of authors, but I found the character not con- 

 stant, and that some of the more decided Pleurotomata have the 

 complete conjunctive tentacula, and not a trace of head or head- 

 veil, but merely the intervention of the usual vertical buccal oii- 

 fice. I am therefore compelled to relieve the genus Murex of 

 these modern dismembennents. I feel confident that none of 

 the so-called British Pleurotomata or Fusi differ generically from 

 Murex. Some of the exotic species may perhaps afford better 

 distinctive generic indices. 



The tentacula are long and taper to a fine point, having the 

 eyes at the external angles of pedicles of not half their length. 

 The foot in front is subtruncate, acutely auricled and labiated ; 

 when in action it is sinuated, long, narrow, tapering to a fine 

 point, and when fully extended reaches beyond the posterior end 

 of the spire ; it is the only species J know of, except the M. cos- 

 tatus, that shows this peculiarity : there is no vestige of an oper- 

 culum, and the lateral scission is rather more apparent than in 

 the two preceding species. The branchial plumes and all the 

 other organs are in exact accordance with the type, M. gracilis. 



The shells exhibit two well-marked varieties ; the one the ty- 

 pical M. linearis, with more regular subdued spiral strise ; the 

 other is more scabrous. The smoother variety is sparingly found 

 in the coralline zone, the scabrous shells in the same zone at 

 Exmouth are abundant. I have only examined the animal of 

 the latter; it is possible the former maybe distinct. Exmouth, 

 3rd August 1850. — Since writing the above I have met with a 

 fine live specimen of the smoother variety, and I am unable to 

 detect a sensible variation in them. 



Murex attenuatus, Montagu et nobis. 

 Pleurotoma aut Fusus, auctorum. 

 This beautiful species is in most respects so similar to the 

 Murex gracilis, the type of this section, that to describe it would 

 be nearly a literal repetition of the account of that animal, ex- 

 cept that the emargination of the outer lip, which scarcely merits 

 that term, is rather a minute hollow shoot than a scission ; there 

 is no operculum. This is a rare animal, but I have examined 

 several from the coralline zone at Exmouth. 



