Mr. W. Clark on the Muricidae. 119 



for days separate assemblages of the two species ; we believe they 

 are distinct. 



Murex, auctorum. 



Cerithium, nonnuU. 

 Cerithio^sis, Forbes. 



Sectio VI. 



Testa conica, elongata, gracilis, turrita, granuloso-plicata. Ca- 

 nalis obliquus, brevis. Columella recta et Isevis. Operculum 

 corneum. 



Murex tuber cularis, Montagu et nobis. 



Animal inhabiting a spiral shell of 10-15 volutions, flake- 

 white, except some sulphur-colour points behind each eye; 

 and behind them, on each side the neck, is a longitudinal 

 band composed of minute brown points ; and anterior to the 

 operculum are two sulphur-colour patches, one on each side. The 

 head is small, compressed ; mouth a vertical fissure in the centre 

 of the fork between the tentacula, from whence, as in the Cana- 

 lifera, a retractile proboscis is exserted. The tentacula are short, 

 inflated, subrotund, slightly triangular at the bases, and for the 

 terminal part flat and more slender, blunt or very little clavate 

 at the tips ; they are frosted hyaline, and edged throughout all 

 the margins with hair-like lines of intenser white, giving them a 

 very elegant appearance ; the foot is also bordered in like man- 

 ner. The mantle forms a branchial fold, which does not float 

 beyond the canal of the shell, and it also lines the slight sinus at 

 the upper angle of the aperture ; the eyes are comparatively close 

 together, rather large, immersed exactly in the centre of gently 

 raised subrotund inflations. The foot in front is scarcely auricled 

 at the external angles, square, with a shallow groove dividing the 

 sole in front from the upper lamina, and forming slight labia; 

 it is gradually constricted in the middle, tapering to a mode- 

 rately pointed termination, with a very deep central longitudinal 

 groove in the posterior half of the foot, terminating at its centre 

 in a minute deep cavity, which undoubtedly pierces the integu- 

 ments, and appears to communicate with the interior of the foot 

 at the junction with the body. 



This decided cavity and the very deep scission are in some 

 measure new features ; they are either to act as aquiferous canals, 

 or to allow the posterior half of the foot to fold, and to assist its 

 doubling at right angles ; the foot is usually carried in advance 

 of about half the length of the tentacula, but in great exertion is 

 sometimes produced to their tips. Though medial grooves in 

 the foot of the Gasteropoda are not unusual, I have never met 

 with one like this. There is a distinct margined operculigerous 



