144 Carl 0. Dunbar, 



equally to the narrowly rounded base. Each whorl rises nearly 

 its entire height above the succeeding one, covering- only the 

 inner half of the flattened upper side of the latter. Umliilicus 

 very narrow or lacking. The early whorls more rounded than 

 the later ones. 



Aperture subtriangular, a little higher than wide, notched 

 above by a broad, short slit, and deeply "channelled at the base. 

 Outer lip thin and extending forward as a lateral crest. Inner 

 lip entire and thin. 



A broad slit-band occupies the horizontally flattened shoulder 

 of the whorl, its inner margin lying in the suture and the outer 

 margin being just above (within) the line where the shoulder 

 begins to curve into the outer side of the whorl. The band is 

 delimited by a sharply depressed line along each edge. It 

 varies from depressed convex to more strongly convex along its 

 median line and concave near the outer margin. The lunul?e 

 show an unusual irregularity in their curvature in the most per- 

 fectly preserved specimen, though this may be a pathological 

 condition. The normal direction seems to be obliquely backward 

 and outward for over halfway across the band, and then forward 

 again with a sharper curvature, as in O. laticincta. On the last 

 half whorl of the best preserved specimen, the lunulse are doubly 

 bent, arching strongly backward near either margin and forward 

 near the center of the band. This irregularity is suggestive of 

 an injury to the exhalent siphon. 



Surface marked by tine uneven lines of growth. On that 

 portion of the upper surface covered by the preceding whorl, 

 these lines curve strongly backward to the slit-band, becoming 

 tangential with its inner margin. From the outer margin of 

 the band they first run sharply forward, but having crossed the 

 periphery, they descend nearly vertically and with a gentle cur- 

 vature across the outer side. They arch strongly backward in 

 crossing the narrowly rounded base, conforming to the margin 

 of the deep channel. Certain of the stronger varices of growth 

 can be followed across the band, and they seem to indicate that 

 the slit was only 5 to 7 mm. deep. 



Dimensions: Height, 34 mm.; width, 24 nun.; height of aper- 

 ture, 17 mm.; width of same, 12 mm.; width of band, about 

 4.5 mm. 



