106 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io« 



on living shells. In some specimens the outer portion of the ribs is 

 worn flat. 



Other material examined: Numerous specimens from localities 

 ranging from Point Barrow to Nunivak Island, the Pribilofs, the 

 Aleutians, the Inland Passage, and Puget Sound. 



Discussion : This is one of the commonest species of Bucainum in 

 the area investigated off Point Barrow base. In general appearance 

 it is most closely allied to B. tenue, but the shell is heavier, the throat 

 is whiter, and the longitudinal folds or plications are stronger and 

 appear to be less numerous than in B. tenue. However, because of 

 the broken or interrupted character of the plications in B. tenue, this 

 difference in number is more apparent than real. In B. tenue the 

 spiral sculpturing is fine and nearly uniform, Avhereas in B. plectrum 

 the spiral threads are coarser and are grouped into fascicles of four 

 or more separated by a narrow interspace. 



Shells of B. ])lectrum from Point Barrow are heavier than those 

 from other localities (with the exception of a large specimen from 

 Chichagoff Island). This characteristic applies to both the shells of 

 the present collection and those in the U. S. National Museum that 

 were collected years ago. Not only is the shell heavier but the groups 

 of spiral threads are also heavier and raised higher. The height of 

 the raised sculpture, or groups of spiral threads, seems to be in direct 

 proportion to the weight of the shell. 



In addition to having a heavy shell, the specimen from Chichagoff 

 Island has constricted sutures, prominent ribs (that do not extend 

 to the canal), a flared mouth, and dark color. It might be said to 

 bear the same relationship to B. plectrum that var. rhodium does to 

 B. tenue. 



In some shells of B. plectrum the longitudinal folds are interrupted 

 or broken, much as in B. tenue, but examination reveals that more 

 often than not this interruption has been caused by injury. In some 

 shells, instead of the spiral threads being crowded into fascicles and 

 separated by distinct grooves or interspaces, the spiral threads are 

 more nearl}^ uniformly spaced and the interspaces are shallow, giving 

 the effect of a missing thread rather than a definite groove. In one 

 specimen examined from Afognak Bay the lip had been broken and 

 in the repaired portion of the shell the sculpture was much finer than 

 in the preceding part of the whorl and the spiral threads were not 

 grouped into fascicles or bands. Had two entire shells had such dif- 

 ferent sculpturing, it is probable that they would be assigned to dif- 

 ferent species. There is also variation in the convexity of the wliorls 

 and in the degree of constriction of the sutures. 



Distribution; The Pacific range of B. plectrum is from Point 

 Barrow to Puget Sound; Johnson (1934) gives the Atlantic range as 



