UNIVALVES TROCHUS. 141 



TROCHUS Top-Shell. 



DESCRIPTION OF PLATE XXVII. 



Drv. I. — Fam. 1. Fig. 5. T. concavus. 



Fwnu 1. Fig. 1. T. Solaris. 

 DiT. W,—-Fam. 1. Fig. 4. T. cookii. 



Fam. 1. Fig. 2. T. iris. 

 Div. III. — Fam. 1. Fig. 3. T. telescopium. .. 



Shell univalve, spiral, more or less conic; aperture somewhat angu- 

 lar or rounded; the Tipper side transverse and contracted; pillar 

 placed ohliquehj. 



THE leading characteristic of the Trochus is the coni- 

 cal shape of its species, the base being broad and the 

 whorls gradually tapering towards the apex. This form 

 prevails with very few exceptions throughout the genus ; 

 some, however, have so strong a resemblance to the 

 Turbo, that (frequent mistakes have been made in their 

 classification. 



A few species of this genus have their surfaces almost 

 smooth ; but the gi'eater number are covered with knobs, 

 spines, tuberculations, or undulations, of which the T. 

 Solaris and the T. imperialis are striking examples. The 

 former has its margin beset with long spines, placed at 

 regular distances, and, when the shell is perfect, re 

 sembling the rays of the sun, as represented in carved 

 work. Many, when uncoated, present a bril liant mother- 

 of-pearl appearance; others have only a pearly aper- 

 ture, and a few exhibit a bronze-like hue. The aper- 



