142 The Ottawa Naturalist. [October 



outline, the umbo being proportionately broader laterally, and the 

 beak straight rather than incurved. 



TrIMERELLA BOREALlS, (Sp. nov.). 



Plate III, figs. 2 and 3. 



Shell unknown ; cast of the interior ot both of the closed 

 valves small, compressed, not far from circular in marginal out- 

 line, but a little wider than long. 



Supposed pedicle valve (Fig. 3). On the cast of the interior 

 ot this valve there are five linear grooves, of unequal length, that 

 radiate forward and outward from the umbo. The middle one, 

 that corresponds to the median plate, extends as far forward as 

 a little past the midlength, the two next to it, on either side, are 

 a little shorter, and the two outer ones shorter still. 



Supposed brachial valve (Fig. 2). On the cast of the interior 

 of this valve there are two flattened conical casts of the platform 

 vaults In the umbonal region, and between them there is a median, 

 longitudinal linear groove, tha: is, however, widest posteriorly 

 and th^t represents the median plate. Each of these casts of the 

 platform vaults is bounded externally by a short but deeply im- 

 pressed linear groove, and the groove that represents the median 

 plate extends from the umbo to within a very short distance from 

 the front margin. 



The only specimen collected is not sufficiently perfect to admit 

 of exact measurements, but the two figures are of the natural 

 size. 



Equan River, first rapid ; one imperfect and slightly distorted 

 cast of the interior of both valves. 



The specimen would seem to indicate a much smaller species 

 that the preceding, with different markings on the interior of at 

 least one of its valves, and a much less produced umbo on the 

 brachial valve. It can scarcely be mistaken for any other Ameri- 

 can species of Trimere/la. 



