490 MUKICID^E. 



The animal displays very energetic locomotion ; it inhabits, 

 at Exmouth, all the sea zones abundantly. 



M. PYGM^EUS, Lamarck. 



Nassa pygmcea, Brit. Moll. iii. p. 394, pi. 108. f. 5, 6 ; (animal) pi. L.L. 

 f. 2, as varicosa. 



This species has been considered a variety of the preceding ; 

 it is closely allied to it, but the animal and shell sufficiently 

 indicate specific distinction. To describe it in the entirety 

 would be a useless repetition ; I therefore only note the devia- 

 tions from its congener. The animal is more slender, and 

 invariably of much lighter colour ; and in addition to the 

 simple emarginate termination of the foot in the M. incras- 

 satus, there are here two long, pointed, apparently tentacular 

 filaments issuing from the fillets of the caudal fork; these 

 are the only material differences. But in this case the shells 

 of the two present so distinctive a contour as to corrobo- 

 rate the malacological variations : that of the M. pygm&us 

 is of much more elegant form, being more produced, the 

 volutions rounder, with additional cancellated ribs, which are 

 not undated, and displaying the white varices (from two to 

 five) of former apertures, which in this species, in fine fresh 

 specimens, are of purple colour ; in M. incrassatus the aper- 

 tures are rufous-brown. 



This animal, at Exmouth, only inhabits the coralline zone, 

 and is much rarer than the M . incrassatus ; it is very lively, 

 and submits to the closest examination. We have kept sepa- 

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

 are distinct. 



Sectio VI. Testa conica, elongata, gracilis, turrita, granuloso-plicata. 

 Canalis obliquus, brevis. Columella recta et Icevis. Operculum corneum. 



CERITHIUM, nonnull. CERITHIOPSIS, Forbes. 



M. TUBERCULARIS, Montagu. 

 Cerithiopsis tubercularis, Brit. Moll. iii. p. 365, pi. 91. f. 7, 8 ; (animal) 



pi. O.O. f. 1 & 2, and pi. 103. f. 6. ? 



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

 white, except some sulphur-coloured points behind each 



