MARINE MOLLUSKS — MACGINITIE 103 



bottom) and one was taken on Apr. 12, 1950, at a depth of 80 feet by- 

 means of a trap through a hole in the ice. The remaining specimens 

 were from depths of 120 to 522 feet, the greatest numbers coming from 

 125 feet (14), 175 feet (7), 150 feet (4), 420 feet (4), 216 feet (3), and 

 453 feet (3). Dead shells were usually inhabited by hermit crabs. 

 The largest specimen is about 70 mm. in height; the smallest, 15.5 mm. 



Other material examined: Numerous specimens from localities 

 from Point Barrow to Plover Bay and to the Aleutians; 1 specimen 

 from Labrador; over 10 from Spitzbergen. 



Discussion: B. glaciate is characterized by moderately convex 

 whorls and strong longitudinally oblique folds that are strongest at the 

 sutures and, in the body whorl, terminate at a strong carina that pro- 

 duces an angle about midway of the whorl. It is spirally sculptured 

 by fine threads grouped in bands of from about 4 to 10, sometimes 15 

 or even more, separated by interspaces varying from one-fourth to 

 one-half the width of the bands. The fine incremental lines that cross 

 these spiral threads give them a wavy appearance, and the interspaces 

 and secondary grooves are likewise crossed by these fine vertical lines. 



In some specimens examined the Avhorls are almost flat (pi. 9, 

 flg. 5), in others the}' are much more convex than in typical specimens. 

 The shells var}^ from relativel.Y slender to almost squat, and although 

 the ones with the more convex whorls are usually the more inflated, 

 there are a few wide, squat shells with almost straight whorls. The 

 number and strength of the longitudinal folds vary markedly; in some 

 specimens the folds fade out before reaching the carina (pi. 9, fig. 2) 

 and in others they remain strong and terminate in a nodule at the keel 

 (pi. 9, fig. 4) ; in some shells these axial folds are regular and in others 

 they are wavj'' and occasionally they are interrupted somewhat as in B. 

 tenue. In some shells the carina or keel is weak (pi. 9, fig. 2), and in 

 a few there is no definite carina (pi. 9, fig. G); in others there may be 

 two carinae (pi. 9, fig. 1) ; in still others there may be a cord both above 

 and below the keel; and in still others there may be 3 cords with no 

 angle formed. In a few shells an angle is formed at the termination 

 of the axial folds without a definite carina being present. Sometimes, 

 instead of being drawn into bands, the spiral iirae are more evenly 

 spaced, giving the wavy effect characteristic of B. angulosum,. In 

 some specimens of B. glaciate the mouth is more rounded than oval 

 and the aperture is much less than one half the length of the shell; 

 in others the aperture is nearly as long as the remainder of the shell. 



In all except one of the 29 specimens examined from Plover Bay, 

 the shells average much heavier than those from other localities and 

 they also increase in size more rapidly. With one exception, a carina 

 is present but the angulation is slight; one specimen has 2 carinae 

 but is not angular. The spiral striae also tend to be gathered into 



