556 CLINTON R. STAUFFER 
the limits of the preserved specimen. It probably bifurcates 
farther out from the calyx. The cross-section of the arms is circular 
and the shape of the arm plates resembles a truncated cone with the 
base upward. It is not quite clear whether the number of arms is 
five or six because the branching in one or two cases begins so 
near the calyx. Dorsal canal extending throughout the arms. 
Horizon and locality.—Onondaga limestone, north shore of Lake 
Erie, three and one-half miles east of Port Dover, Ontario. 
Poterioceras canadensis n.sp. 
PraTE I, Fics. 2-5 
Shell small, tapering both ways from the base of the chamber 
of habitation or last air chamber, and extending to a rather blunt 
point at the apex. Ventral side strongly curved, dorsal side nearly 
straight but curving slightly upward near the apex. Transverse 
section subcircular. 
Chamber of habitation relatively large, bemg about two-fifths 
of the length of the shell, and more or less pear-shaped. 
Air chambers regular, increasing slightly in thickness from the 
apex to the chamber of habitation. Septa smooth, thin, and con- 
cavity rather shght. Suture straight and horizontal. 
Siphuncle small and marginal on the ventral side. 
Aperture subtriangular. Hyponomic sinus well developed. 
Surface of shell nearly smooth, marked only by fine lines of 
growth. 
Horizon and _ locality.—Onondaga limestone. Hamilton’s 
Quarry, Gorrie, Ontario. 
Rhipidomella intermedia n.sp. 
PLATE II, Fics. 1 AND 2 
Shell subcircular and more or less lenticular in transverse 
section. Hinge line equal to slightly more than half the width of 
the shell. Both valves are convex. The pedicle valve with a 
flattened area along the median line just in front of the middle and 
extending to the front margin, where it becomes a broad indistinct 
sinus. Over the corresponding surface of the brachial valve there 
is a broad convexity. 
