TBOCHTJS. 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 T. 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 T. conulus of authors is only a slender variety of 

 this species/ but generally the examples in the cabinets are 

 exotic. 



T. MONTAGUI, Gray. 

 T. Montagui, Brit. Moll. ii. p. 511, pi. 65. f. 10, 11. 



As the animal of this species, though its shell is not umbi- 

 licated, closely resembles the T. 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, fringed 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 split into 

 five short, flattish, frosted cilia, fimbriated at the sides ; the 

 eye-pedicles are clothed with thick-set seta?, far longer than 

 in the T. 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 T. serpuloides 



