1902] Whiteaves On the Genus Trimerella. 141 



those that have previously been described, and that may be pro- 

 visionally named and characterized as follows : 



Trimerella Eouanensis (Sp. nov.). 

 Plate II, figs. I & 2, and Plate III, fig-, i. 



Shell rather large, attaining to a length of upwards of three 

 inches. Pedicle valve flattened somewhat obliquely, most convex 

 and deepest at a short distance from the beak, nearly as wide as 

 long, broadly rounded in front, more narrowly rounded at the 

 sides, and obtusely pointed behind, the umbo and beak being 

 moderately produced, their lateral margins meeting at an angle 

 of about gS'', and the beak gently incurved. Characters of the 

 interior of this valve unknown. 



Brachial valve regularly but moderately convex, most pro- 

 minent externally 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 nar- 

 rowly 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 repre- 

 sents the median plate and that extends from the umbo almost to 

 the front margin, also with a lateral and slightly divergent linear 

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

 beyond the midlength. 



Surface of both valves marked only with a few distant con- 

 centric lines of growth. 



Falls of the Equan River ; one imperfect and badly preserved 

 specimen with both valves in siiii, 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 bo- 

 long to the group of T. acuminata rather than to that of T. grandis, 

 though it seems to be always much shorter and wider than 

 T. acuminata, T. Ohioensis, or T. Lindstrwniii. The marginal 

 contour of its brachial valve is not very unlike that of T. Lind- 

 strwmii, but in the latter this valve is represented as flattened 

 anteriorly to the umbo, and its pedicle valve has quite a different 



