110 PROCEEDINGS OF THE NATIONAL, MUSEUM tol. i06 



Eighteen specimens of var. normale were collected: 6 (37 to 41.5 

 mm.) washed ashore in September 1949; and 12 (30.5 to 43.5 mm.) 

 were taken in screen traps between Mar. 10 and June 13, 1950, at a 

 depth of 37 feet. 



With the exception of one from 522 feet and one from 213 feet, 

 all 69 of these specimens came from depths of 110 feet or less, and 

 39 were taken in winter by means of screen traps. The shells were 

 frequently partially covered with hydroids. 



Other material examined: About 17 specimens of B. angulosum 

 from Bernard Harbor, Point Barrow, Icy Cape, and Kotzebue Sound; 

 2 from Spitzbergen. 



Four specimens of var. suhcostatum, including the figured type, 

 from Point Barrow, Station 24, Canadian Arctic Expedition, and 

 Icy Cape. 



About 15 specimens, including the type, of var. transliratum from 

 locahties from Point Barrow to Unimak Island in the Aleutians. 



Over 100 specimens, including the type lot, of var. normale from 

 localities from Bernard Harbor to Point Barrow, to Kotzebue Sound; 

 1 from eastern Greenland; 1 from Spitzbergen. 



Discussion: In both true B. angulosum and var. normale there are 

 fine to medium-fine spiral threads that are crossed by about equally 

 strong incremental fines that give the surface a wavy or shallowly 

 reticulate appearance. In the forms of var. suhcostatum and var. 

 transliratum there is more of a tendency toward fasciculation of the 

 fine spiral threads and the incremental fines are not so prominent as in 

 the above two forms, but they are quite evident and exert enough 

 influence to produce a wavy effect and make fines across the shaUow 

 interspaces. 



But if one examines a sufficient number of sheUs, it is possible to 

 find almost every intergradation between the two types of sculpture. 

 In some sheUs of the transliratum variety the spiral fines are nearly 

 evenly spaced and there is fittle evidence of an interspace. It is also 

 possible to find sheUs with both types of sculpture on the same shell. 

 And in some shells of the B. angulosum type the sculpturing approaches 

 that of B. cilialum, with a heavier spiral cord alternating with a weaker 

 one and with the incremental lines no stronger than the weaker spiral 

 cord, or perhaps not so strong. 



One specimen that was assigned to var. transliratum has a much 

 heavier than typical shell with a flaring fip — both characteristics 

 suggesting B. angulosum; it has two spiral carinae that suggest var. 

 transliratum (the anterior carina is weaker than the posterior one and 

 the sheU is slightly nodulous at the junction of the posterior carina 

 and the ribs) ; the sculpture is that of var. transliratum. Four shells 

 that were assigned to var. suhcostatum have discrepancies that make 



