150 AMERICAN JOURNAL 



* Whorls shouldered ; aperture broadest above. 



B. Polare, Icy Cape, Arctic Ocean north of Behring's 

 Straits. 

 ** Whorls scarcely shouldered ; aperture broadest be- 

 low. 

 B. Grcenlandicum, Davis' Straits, Fossil at Montreal. 

 2. Shell thick and strong ; aperture patulous, outer lip 

 sinuated. 



* Shell elongated. 



B. Donovani, New Foundland, Greenland ? 



** Shell ovate. 

 B. glaciale, Arctic Ocean, Greenland, Spitzbergen. 

 b. Primary transverse ridges convex; secondary grooves 

 very distinct. 

 B. angulosum, Behring's Straits, Icy Cape. 

 B. Body-whorl not angulated. 



a. Aperture narrow. 



1. Primary ridges flat. 



B. striatum, Sea of Ochotsk. 



2. Primary ridges convex ; a strong, tooth-like plait on 



the columella. 



B. ciliatum, Behring's Straits to Greenland, South to Nova 

 Scotia. 



b. Aperture broad. 



1. Longitudinal folds numerous, often interrupted, or in- 



terposed. 



* Primary ridges flat. 



B. plectrum, BehriDg's Straits, Fossil at Portland, Maine* 



* Variety ? If distinct, Dr. Stimpson proposes for it the name Bucci- 

 num Packardii. 



** Primary ridges obsolete; secondaries conspicuous, 



crowded. 



B. tenue, Arctic Ocean, South to Labrador. 



2. Longitudinal folds not interrupted or interposed. 



* Shell thick and coarsely striated. 



f Sinus of outer lip near the suture, columella short. 

 B. undulatum, Labrador to New Jersey. 



ft Sinus of outer lip near the middle, columella pro- 

 jecting. 

 B. undatum, Coast of Europe from Southern Norway to 

 Portugal. 



