Mr. W, Clark on the Muricidse. 121 



part of the shell. This species is one of the most typical of the 

 Pleurotomata of British authors, but its distinguishing feature, 

 the sinus, is not sufficiently stable in the British species to give 

 them the impress of generic distinction. 



The head appears to be a very short protrusion of the red ver- 

 tically cloven proboscis, which can be exserted to a great length ; 

 it contains the usual short spiny tongue and other organs of the 

 buccal apparatus, consequently in this species 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 be- 

 tween the so-called Fusiis and Pleurotoma, but the character 

 as regards the British Pleurotomata is very variable and cannot 

 be depended on, as some decided ones, as to the shell, have not a 

 trace of an exserted head or veil, and whose tentacula at their 

 bases are conjunctive, with only the separation of the proboscidal 

 fissure; and in their genus Fusus the same discrepancies occur, 

 as in some of the minor species the tentacula coalesce, whilst in 

 others the conjunction 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, acu- 

 minated 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 the 

 Aporrhais pes pelecani that has a corneous operculum with a still 

 narrower aperture. The branchiae are semilunar, one large, one 

 smaller, of a dark brown colour ; immediately above the larger 

 one are the coarse pale yellow mucous filaments, which are edged 

 with a dark border. The organe generateur wMe is a very long, 

 narrow, pale yellow, white, strap-shaped appendage, pointed at 

 the end, springing under the right tentaculum, and lies doubled 

 up and reflected back in the branchial cavity. The ovarium and 

 liver occupy all the posterior volutions, and run mixed together 

 to near the pylorus ; the two organs are easily distinguished, the 

 ovarium being pale yellow, and the liver red-brown. In the male 

 the testis replaces the ovarium. I have a little exceeded the 

 limits of ordinary description on account of this animal being 

 the type of the section. 



This elegant species is sufficiently abundant in the coralline 

 zone at Exmouth. 



