TROCHUS. 527 



has a somewhat rounded figure ; the breadth, which 

 scarcely exceeds the length, is superior to one half of the 

 basal diameter. The outer lip is simple, acute, and rather 

 broadly margined with black or dusky green. It is con- 

 siderably and continuously arcuated, yet is less convex in 

 front than behind ; it recedes so greatly anteriorly as to 

 expose a large portion of the internal silvery nacre. The 

 white pillar-lip is much bent, being subangulately curved 

 in the middle, the nacre is only spread, and that too, 

 sparingly upon the anterior portion of it. The pillar, 

 which is broad, appressed, slightly oblique, and often a 

 little concave in front, has the line of demarcation between 

 it and the surrounding area almost entirely obsolete ; it is 

 furnished with a somewhat tooth-like projection at its 

 inner edge, and sometimes (yet rarely) with a single indis- 

 tinct transverse groove nearly opposite the middle of the 

 umbilicoid indentation. The ordinary diameter is about 

 an inch in both directions, a size frequently much exceeded 

 in those worn and aged individuals that are generally 

 rejected from our cabinets. 



The operculum differs from that of its allies, and is 

 loosely spiral in the centre. 



The animal has the muzzle finely serrated at the margin, 

 and of a dusky hue ; the head-lobes are semicircular, and 

 at their bases the head is marked with closely-set black 

 lines. The tentacula are long, subulate, and ringed with 

 closely-set fine black annulations. The eye-peduncles are 

 stout, edged with yellow at their extremities, and bear 

 black eyes. The neck-lappets are pale green, the inner one 

 fringed at the edge, the outer one plain. The lateral veils 

 are of a pale dull green hue, with a drab fringe at their 

 margins ; on each side there are three long filiform, ex- 

 tremely delicate cirrhi, white, annulated with dusky and 



