008 UNITED STATES GEOLOGICAL SUEVEY OF THE TERRITORIES. 



the breadth of the outer whorl from Oie dorsal to the ventral side, showing 

 about one-third of each inner volution. Whorls increasing rather vapidly in 

 size, particularly in convexity, sloping on each side from near the umbilicus 

 (with a slightly convex outline) toward the periphery, and rounding abruptly 

 into the umbilicus on the inner side, each of those within deeply embraced 

 by the succeeding turn. Aperture transversely reniform or sublimate. Sur- 

 face ornamented with rather small, regular, rounded costa?, which pass nearly 

 straight across the sides of the whorls, and arch slightly forward in crossing 

 over the periphery, on which from thirty-six to forty of them may be counted 

 to every turn ; each of those commencing at the umbilicus, usually there a 

 little enlarged, especially on the larger whorls, so as to form a small sub- 

 nodose prominence. Beyond these, they all (particularly on the inner whorls) 

 bifurcate regularly once, near the middle of each side, and on the larger turns 

 others are also intercalated between, so as to make the number on the periph- 

 eral side five or six times as great as at the umbilicus. 



The septa are rather crowded, and provided with branched and deeply 

 sinuous lobes and sinuses. The siphonal lobe is about one-fourth longer 

 than wide, nearly obovate in form, and ornamented with three principal 

 branches on each side, the two terminal of which are larger than the others, 

 and each provided on the outer side with two or three more or less digitate 

 lateral branchlets, while the inner parallel margins are merely sharply ser- 

 rated. The first lateral sinus is of about the same size as the siphonal lobe, 

 a little oblique, nearly oblong in form, and divided at the extremity into two 

 tripartite and obtusely digitate branches, of which the one on the outer side 

 is larger than the other; behind these, it is provided on each side with two 

 alternating lateral branches with sinuous margins. The first lateral lobe is 

 narrower and shorter than the siphonal lobe, and provided with two principal 

 branches on each side, the two terminal of which are much larger than the 

 others, and of unequal size, the one on the right or peripheral side being the 

 larger. Both of these terminal branches are distinctly bipartite, the subdi- 

 visions being ornamented with several branchlets and smaller digitations. 

 The second lateral sinus is about half as wide and nearly two-thirds as long as 

 the first, more or less oblique, and rather deeply divided at the extremity 

 into two subequal, bifurcating, and obtusely digitate terminal branches. The 

 second lateral lobe is as long as the second lateral sinus, but a little narrower, 

 and ornamented with three variously digitate terminal branches, the middle 



