Family TRICEOTROPID.^. 



Shell thin, turbinated, cnrinated, the ridges bearing epidermal 

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

 lated or subehanneled below, lip sharp, columella obliquely 

 truncated, operculum generall}' lamellar, with apical nucleus. 

 (Pi. 10, .tig. 38). 



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

 with eyes about their middle ; foot elongated ; siplion very 

 short, but evident. 



Central tooth of the radula subquadrangular, multicuspid, 

 lateral large, transverse with 'finely crenulated margin, two 

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



PI. 7, fig. 37. 



Genus TRICHOTROPIS, Brod. and Sowb., 1829. 



Characters those of the family. Thei'e 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. 



Fere?!a, Gra}', 1857 (not H. and A. Adams, 1851), is a synonym. 

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



Shell widel}' 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, 18fil. 

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

 whorls convex, cancellated with elevated spiral ribs and longi- 



(40) 



