TROCHUS. 493 



raised spiral fillets, that typically encircle the shell, are 

 granular ; elsewhere they are simple and round-topped 

 (occasionally, however, as in the solid dark produced 

 variety we have figured, the subsutural one exhibits, at 

 intervals, an obscurely subgranose appearance) ; these cos- 

 tellar striae are sometimes coarse, few, and rather distant, 

 sometimes numerous, very fine, and not much elevated. 

 The inferior one of each whorl which immediately pre- 

 cedes the well-defined suture, is always conspicuous for 

 size or prominence, and is preserved even in the broad- 

 based smooth variety, where the others are wholly or 

 partially absent. These spiral lines become flatter upon 

 the base of the shell, where they either become indis- 

 tinct or transmuted into sulci. The fine and close-set 

 wrinkles of increase are at times perceptible upon the 

 more rugged individuals, and diverge, as it were, from 

 the axis of the shell. The base is imperforated, and, 

 except in the smoother specimens, but little convex ; the 

 shelve is generally moderate. The mouth is obliquely 

 rhombic, and considerably broader than it is long; in 

 general it occupies about two-fifths of the entire length 

 of the shell, and about one half the basal diameter ; no 

 sculpture distinguishes it, beyond the traces of the external 

 fillets. The outer lip is very acute ; the pillar is oblique, 

 more or less curved, broad, rounded yet appressed, and 

 with its nacre often interrupted or notched at the base 

 by the jutting into it of the white callus, which bounds 

 it externally. Our finer specimens measure an inch and 

 three-eighths both in length and breadth ; but these di- 

 mensions, although greatly beyond the average, are by no 

 means the extreme limit of the size attained. 



The animal is always brightly coloured with reddish 

 brown, whatever may be the hue of the shell. Its head 



