TROCHUS. 307 
and head-lappets ; the former, though nearly as long as in its 
congener, and as finely fringed, is much narrower; like it, 
there are the four vibracula on the upper lobe, the same mar- 
ginal fringes, and a multispiral operculum of exactly similar 
aspect. The other variations are those of colour, the foot 
being on its upper surface dark mottled brown, and smooth, 
instead of papillose, citron-yellow, and with anastomosing 
lines ; beneath, instead of being white, it is flesh-colour in the 
centre, shading into pale drab at the margin. ‘The front por- 
tion of the tentacula is dark brown, with a dull, indistinctly 
defined longitudinal line, not so well marked as in 7. granu- 
latus ; and the pedicles on which the eyes are fixed are rather 
longer and more slender. The neck-lappets on both sides 
are large, subrotund, white, symmetrical, plain at the edges, 
though often sinuated by the action of the animal. I am 
confident that in this species there are no head-lappets ; it is 
bald, smooth, of a dark brown colour. 
This species, with the shell varying in contour and colour, 
is found most frequently in the coralline zone, but it is also 
often taken in the littoral and laminarian levels, of inferior size. 
The English 7. conulus of authors is only a slender variety of 
this species, but generally the examples in the cabinets are 
exotic. 
T. Monracut, Gray. 
T. Montagui, Brit. Moll. ii. p. 511, pl. 65. f. 10, 11. 
As the animal of this species, though its shell is not umbi- 
licated, closely resembles the 7. tumidus, it is only necessary to 
point out the variations. The tentacula are thicker, rounder, 
and decidedly more clavate, sometimes appearing spatulate at 
the tips, frmged with intenser or closer setose filaments, and 
the margin of the buccal disk is finely crenated ; the head-lobes, 
instead of being delicately denticulated, are each spht into 
five short, flattish, frosted cilia, fimbriated at the sides; the 
eye-pedicles are clothed with thick-set sete, far longer than 
in the 7. tumidus; the anterior angles of the foot in both 
species are furnished with short, horizontal, straight, linear 
auricles, not so much curved and extended as in 7. serpuloides 
xe 
