280 APORRIIAIDiE. 



Operculum, T. borealis, fig. G, n, 6, h. Shell, T. bicari- 

 nata, Broderip and Soiverhy, fig. 6, c. 



There are more thau a dozen species, most of them 

 being natives of the Boreal seas; the few from warmer 

 latitudes were dredged from very deep water. 



Species of TricJiotropis. 



acuminata, Jeffr. conica, Moll. 



Atlantica, Beclc. dolium, Petit. 



bicai'inata, Brod. and Soiv. flavidula, Hinds. 



borealis, Brod. and Soiv. inermis, Hinds. 



cancellata. Hinds. iusignis, Midd. 



clathrata, A. Adams. umbilicata, Broivn. 



Sub-gen. iphjnoe, H. and A. Adams. 



Shell thin ; aperture subtrigonal; axis widely and deeply per- 

 forated. 



ciliata, Kriiger. unicarinata, Sow. 



Fam. APORRHAIDJE. 



Lingual membrane with seven series of teeth (S'TS), 

 the median hooked, denticulated, the first lateral uncinate, 

 the second and third claw-shaped. Rostrum elongate, 

 tapering; tentacles subulate, bearing the eyes on slight 

 prominences at their external bases. Mantle with the 

 outer margin expanded or lobed, and with a rudimentary 

 siphon in front, bent to the right. Foot small, oblong, 

 simple. 



Operculum annular, ovate or pointed, the nucleus small, 

 apical. 



