LEIOSTRACA. 237 



polygyra, A. Adams. solidula, Adams and Reeve. 



porcellana, A. Adams. subangulata, Soiv. 



pusilla, Sotv. teinostoma, A. Adams. 



pyramidalis, A. Adams. tortuosa, Adams and Reeve. 



recta, C. B. Adams. vitrea, A. Adams. 



Genus NISO, Risso. 



Shell subulate, turreted, many-whorled, axis perforated ; 

 aperture oval, anteriorly angulated ; outer lip simple, 

 acute ; umbilicus very deep, extending as far as the 

 apex of the spire. 



Syn. Bonellia, Desh., not Rolando. Janella, Grat., 

 not Gray. 



Ex. N. terebellum, Chemnitz, pi. 25, fig. 2. Oper- 

 culum, N. brunnea, Souerby, fig. 2, a, 2, b. 



In this genus the axis of the shell is widely umbi- 

 licated, and the aperture, besides being angulated, is 

 curiously modified in consequence ; there are about 

 seven species known, some of great beauty and rarity. 



Species of Niso. 



brminea, Soiv. interrupta, Soiv. 



candiclula, A. Adams. splendidula, Soiv. 



gouiostoma, A. Adams. terebellum, Chem. 

 imbricata, Sow. 



Genus LEIOSTRACA, H. and A. Adams. 



Shell turreted, subulate, flattened, widest from side to 

 side, polished, smooth, semipellucid ; sides with a thin 

 varix extending as far as the apex of the spire ; aperture 



