306 TKOCHIDJ3. 



with a red-brown narrow longitudinal medial line; when 

 fully on the march, it loses the auricular angles, becoming 

 posteally narrowed and elongated into a sharp point : the edge 

 of the main sole is clothed with a short, close, exceedingly fine 

 white fringe, only visible in water by the aid of a good lens ; 

 it is an error to describe it as crenated; the colour beneath is 

 yellowish-white, above lemon-yellow, sprinkled with irregular 

 fine brown lines and points. When not in extension it has a 

 papillose aspect, but in full action appears divided by fine 

 anastomosing lines into irregular lozenges, resembling coarse 

 shagreen : from the upper surface a membrane or lobe springs, 

 carrying its walls erect, on which, at some distance from its 

 posterior origin, is imbedded a circular multispiral corneous 

 operculum, having the close-set striai of increment crossed by 

 fine oblique lines ; the accessorial lobe then pursues its course 

 on each side the main foot to nearly the anterior end, the 

 margins being clothed with strong, rather coarse white fringe ; 

 and in addition, on each side, there are four longish, cylin- 

 drically tapering, pointed, equidistant white vibracula, that 

 issue from a tubercular sheath, into which they can be par- 

 tially retracted; these appendages are in constant motion. 

 The internal organs present no unusual peculiarity, except the 

 reproductive elements and branchial plume, which, as they 

 offer some anomalous points, will be mentioned at the end of 

 the specific descriptions. 



This beautiful creature is an inhabitant of the coralline 

 zone, at Exmouth, very rarely appearing in the littoral or 

 laminarian limits ; the pure snow-white variety is occasionally 

 taken at the same place. Our remarks are perhaps too 

 diffuse, but this species is selected as the type of this section, 

 though, from the similarity of the tribe, almost any other 

 would have served. 



T. ZIZIPHINTJS, Linn, et Auct. 

 T. ziziphinus, Brit. Moll. ii. p. 491, pi. 67- f. 1-6. 



The animal inhabits a strong, conical, brown or white shell 

 of 6-8 spiral, smoothly striated volutions. It is nearly similar 

 to the T. granulatus ; the principal variations are in the foot 



