Mr. E. A. Smith on Arctic Mollusca. 135 



and is furnished with only two fangs : they 



are subequal in length ; but the inner one is 



slightly the stouter. The other lateral plate 



has three teeth, of which the outermost is 



longest, the median smallest and at the 



base joins the inner fang. The median plate Radulaof 



bears four small conical denticles. Buccinmn sericatmn. 



The only example of this species is a young shell. It 

 agrees in all respects with Hancock's admirable description, 

 except that the cilia of the epidermis are apparently closer 

 together than in the type, in which they are said to be " not 

 much crowded," whilst in the specimen before me there are 

 about three in the space of a millimetre. The surface of the 

 shell beneath the remarkable epidermis is very curiously 

 wrinkly-striated. The operculum is roundish, greenish yellow 

 on the inner side, and dirty yellow exteriorly ; and the nucleus 

 is rather less central than in B. Belcheri. 



This species is considered a variety of B. groBnlandicum, 

 Chemnitz, by Jeffreys (see ' Annals & Mag. Nat. Hist.' April 

 1877, p. 323). 



Taking into consideration the remarkable difference of the 

 epidermis and of the radula, I think there can be no doubt of 

 the specific distinctness of the two forms. Besides these 

 differences there are others of form and sculpture. 



Trichotro^is tenuis^ sp. nov. 



Shell very thin, light, semitransparent, glossy white, glo- 

 bosely turbinate, widely and openly umbilicated, clothed with 

 a dirty-yellowish epidermis, produced on the keels of the whorls 

 into close-set, very short, bristle-like filaments, and rather 

 coarsely obliquely striated, or rather lamellated, marking 

 periods of growth ; whorls 6, th^ two apical ones smooth and 

 rounded, the three following beautifully sculptured with raised 

 oblique lines of growth and minute spiral strife, keeled and an- 

 gulated a trifle above the middle, convexly sloping above the 

 keel and nearly straight beneath it ; last whorl large, encircled 

 with three faint keels, two near the middle and the third at the 

 base, bordering the umbilicus ; aperture subcircular, occupying 

 about 1 yof the entire length of the shell, whitish within, streaked 

 with irregular, curved, yellowish-olive stripes ; the peristome is 

 continuous, thin, with the epidermis produced beyond its ex- 

 treme edges ; columella white, arcuate, with a slight shallow 

 channel at its base. 



Greatest length 33 millims., diam. of last whorl above the 

 aperture 18, greatest diam. 30; aperture 184 long, nearly 17 

 wide. 



