490 MURICIDA. 
The animal displays very energetic locomotion ; it inhabits, 
at Exmouth, all the sea zones abundantly. 
M. pyemaus, Lamarck. ; 
Nassa pygmea, Brit. Moll. iii. p. 394, pl. 108. f. 5,6; (animal) pl. 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 MW. 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 im this case the shells 
of the two present so distinctive a contour as to corrobo- 
rate the malacological variations: that of the M. pygmeus 
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, im 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 levis. Operculum corneum. 
CrritHium, nonnull. Crriruiorsis, Forbes. 
M. tusercuiaris, Montagu. 
Cerithiopsis tubercularis, Brit. Moll. iii. p. 365, pl. 91. f. 7,8; (animal) 
pl. 9.0. f. 1 & 2, and pl. 103. f. 6. ? 
Animal inhabiting a spiral shell of 10-15 volutions, flake- 
white, except some sulphur-coloured pomts behind each 
