UNIVALVES. TROCHUS. 103 



distances, resembling, when the shell is perfect, the rays 

 of the sun as represented in carved work: it has also a 

 most beautiful gold color, which occasionally shines forth 

 through the ochreous surface of the shell, and of course 

 adds materially to the similitude. The T. imperialis is 

 generally of n dull olive color, but there is a rare variety 

 of it which has a pinkish cast, and is known by the name 

 of the Pink Sun : they are both from the South seas. 



Of the imperforated species, the most characteristic are 

 the T. vestiarius, T. labio, and T. tuber, the latter of 

 which very much resembles a Turbo. 



The T. iris, when uncoated, is celebrated for the splen- 

 did metallic lustre which illumines its surface, and for the 

 vivid play of iridescent colors which it exhibits when 

 held in different positions and lights. 



The T. Cookii, from Cook's Bay, has its aperture closed 

 with a horny lid or operculum, to secure the inhabitant 

 when retired within its shell. This appendage is not un- 

 frequent in many of the Univalve genera; it is affixed to 

 the animal, which, as it retreats into the spiral whirls of 

 its shell, draws the operculum in along with it, to a parti- 

 cular situation of the aperture, where, from the extreme 

 accuracy of its adjustment, it perfectly closes the orifice, 

 and thereby forms a complete barrier against any outward 

 attacks. 



The operculum varies in shape according to the form 

 of the mouth it has to close : in some instances it is elong- 

 ated, and has a horny appearance; in others, it is cir- 

 cular, and of a very compact testaceous substance; some 

 are perfectly smooth, and others strongly granulated. 



Tlie T. conchyliophorus is a very curious and remark- 

 able species; for it is invariably covered with other sub- 

 stances, strongly adhering to the whirls of the shell. 



