114 ROYAL SOCIETY OF CANADA 



a concave doreal side and a i-oundod. convex, ventral side ; about one- 

 third of the iloi-stil side is concave and the remainder toward the hiteral 

 angles, convex. The ventral side of this species has not been seen, but a 

 section of the tube near the orifice shows it to have been rounded and 

 stroiii^Iy convex. 



The rate of tapering is about 1 to 8. A})icai angle about 1°. 



Sculj/ture. — The dorsal side of the tube has line, closely set striic of 

 growth, directly transverse, just discernable with a strong lens. 



Size. — This species has a width at the aperture of 2 mm, and a length 

 of about 15 mm. 



This species belongs to Holm's division Plicati of Orthotheca and is 

 related to JI. (0.) alunis, Holm, which in Sweden extends through the 

 Paradoxidea Beds ; but it is not half of the diameter of that species, and 

 is a more elongated form. 



Orthotheca bayonet (PI, VII.. ligs. la to e), 



Orthotheca bayonet, Nat. His. Soc, N.B., Bull, xviii., p. l'J3, pi. iii., tigs, la to e. 



Tube thin ; section triangular ; the two ventral slopes as flat as the 

 dorsal. The dorsal side slightly concave in the middle, but somewhat 

 convex toward the lateral angles ; it has two faint longitudinal ridges, 

 which in some cases are scarcely discernable, bounding the dei)ressed, 

 central area ; this area is more than two-thirds of the whole width of the 

 dorsal side. 



The ventral side is strongly convex at the middle, with a rounded 

 angle at the axial line ; on each side of this is a faintly marked narrow 

 longitudinal ridge, sometimes not traceable. Each half of the ventral 

 side is convex toward the median Hne of the tube and concave toward the 

 lateral angle. 



The oritice declines at the lateral angles on the ventral side, where 

 it is notched ; the edge of the orifice on the dorsal side is slightly convex 

 outside the longitudinal ridges near the lateral angles, and concave in the 

 space between these ridges ; the aperture is thus somewhat lower on the 

 dorsal than on the ventral side. 



Sculpture. — The outer surface is finely granulated, and is traversed 

 by very tine stria? (visible only with a lens) that conform in their course 

 to the shape of the aperture ; there are also large shallow undulations of 

 growth on the two slopes of the ventral side. 



Size. — This tube has been found only in fragments ; the largest 

 observed would indicate an aperture 8 mm, across, and the taper of the 

 shell is as 1 to 5 (one is 1 to 4). Apical angle 10°. The length of the 

 complete shell may be 40 mm. 



This tube is so thin that it is liable to distortion, and also liable to 



