1907 ] Canadian species of Peltoceras 81 



P. atkleta and other known species of the genus, and mav be 

 provisionally named and described as follows: 



Peltoceras occidentale, sp. nov. 



Peltoceras occidentale; a, side view of the only specimen collected; b, 

 portion of .venter of the same, showing four primary bifurcating ribs, 

 alternating with four secondary simple ones ; c, outline of transverse 

 section of the outer volution of the same, near the aperture. All the 

 figures of the natural size. 



Shell widely but very shallowly umbilicated on both sides, 

 the umbilicus occupying fully tv>'o-thirds of the entire diameter. 



Whorls slender, increasing very slowly in size, in close con- 

 tact throughout, but without embracing, flattened and widest on 

 the venter (as shown in figure c) angulated at its junction with 

 each side, and narrowing convexly and somewhat obliquely 

 inward, to the rather narrow dorsum, which is impressed longi- 

 tudinally bv a very shallow furrow of contact. 



Test unknown; surface of the cast of the interior marked 

 with numerous, nearly straight transverse ribs. On each of the 

 sides all the ribs are simple and unbranched (as shown in figure a) 

 which rey^resents one of the sides. But, at the ventrolateral 

 angulation on each side of the outer whorl, each primary rib swells 

 into a comparatively large, circular and flattened tubercle, then 

 bifurcates (as represented in figure b) or trifurcates in passing over 

 the venter, and finally coalesces with a similar tubercle on the 

 ventrolateral angulation of the other side. The secondary ribs 

 are as long as the primaries, but the former are neither tuber- 

 culated on the outer mtargin of the outer whorl, nor divided on the 

 venter, though thev are not infrequentlv interrupted in or by the 

 close proximity of a tubercle on one of the alternating primaries. 



Sutural line unknown. 



