250 

 • 



" Brachial valve regularly but moderately convex, most prominent ex- 

 ternally at or about the midlength, a little wider than long, broadly 

 rounded in front and less so at the sides, as in the pedicle valve, but 

 abruptly contracted at the umbo, which is narrowly rounded and but 

 slightly produced, while its beak is strongly incurved and recurved. Casts 

 of the interior of this valve are marked with a longitudinal, linear, median 

 groove, that represents the median plate and that extends from the umbo 

 almost to the front margin, also with a lateral and slightly divergent lin 

 ear groove, on each side, that extends from the umbo to a little beyond 

 the midlength. 



" Surface of both valves marked only with a few distinct concentric lines 

 of growth." 



Portage road at falls : " one imperfect and badly preserved specimen 

 with both valves in situ, a nearly perfect pedicle valve, three imperfect 

 brachial valves with most of the test preserved, and a cast of the interior 

 of a large brachial valve. 



" Judging by these specimens, this species would appear to belong to the 

 group of T. acuminata rather than to that of T. grandis,tho\igh. it seems 

 to be always much shorter and wider than T. acuminata, T. Ohioensis or 

 T. Lindstroemii. The marginal contour of its brachial valve is not very 

 unlike that of T. Lindatrcemii, but in the latter this valve is represented 

 as flattened anteriorly to the umbo, and its pedicle valve has quite a dif- 

 ferent outline, the umbo being proportionately broader laterally, and the 

 beak straight rather than incurved. 



Trimerella boeealis, Whiteaves. 



Plate 25, figs. 3 <fe 3 a. 



Trimerella borealis, Whiteaves 1902. Ottawa Naturalist, vol. XVI, p. 142, pi. 



3, figs. 2 & 3. 



" Shell unknown ; cast of the interior of both of the closed valves small, 

 compressed, not far from circular in marginal outline, but a little wider 

 than long. 



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

 valve there are five linear grooves, of unequal length, that radiate for- 

 ward 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. 3). "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, that is, however, widest posteriorly and that represents the nledian 



