FAMILY TRICHOTROPIDJE. 



Shell thin, turbinated, carinated, the ridges bearing epidermal 

 fringes in fresh or living specimens, umbilicated ; aperture angu- 

 lated or subchanneled below, lip sharp, columella obliquely 

 truncated, operculum generally lamellar, with apical nucleus. 

 (PL 10, fig. 38). 



Animal with a short, broad head ; tentacles somewhat distant, 

 with eyes about their middle ; foot elongated ; siphon very 

 short, but evident. 



Central tooth of the radula subquadrangnlnr, multicuspid, 

 lateral large, transverse with finely crenulated margin, two 

 marginal teeth on either side, curved, sharp, simple (2 ri'1'2). 



PI. 7, fig. 37. 



Genus TRICHOTROP1S, Brod. and Sowb., 1829. 



Characters those of the family. There are about 15 species, 

 inhabiting Arctic seas. Fossil, in the English Crag. 



Trichophora, Desh., 1830, is a synonym. The name signifies 

 " hairy keel." 



The following sections of Trichotropis have been proposed : 

 they have little value : 



Section TRICHOTROPIS (sensu stricto). T. BICARINATA, Sowb. 

 Section ARIADNA, Fischer, 1864. 



Shell without epidermal fringes. T. BOREALIS, Brod. and Sowb. 



Has the epidermal fringes in fresh specimens. 



Verena, Gray, 1857 (not H. and A. Adams, 1854), is a synonym. 

 Section IPIIINOE, H. and A. Adams, 1854. 



Shell widely umbilicated, aperture subtriangular. T. UNICARI- 

 NATA, Sowb. 



The width of the umbilicus varies in the species, so that the 

 group is unimportant in its characters. 



Subgenus ALORA, H. Adams, 1861. 



Shell ovate-fusiform, slightly umbilicated, thin ; spire elevated ; 

 whorls convex, cancellated with elevated spiral ribs and longi- 



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