11 



in front of the mid-length ; umbo narrowly rounded ; apical angle about 

 90 ; front margin broadly rounded or gently convex ; sides, in the upper 

 half, somewhat straight and uniformly converging from a little below the 

 mid-length to the beak ; in the lower half uniformly rounded into the 

 front margin. The beak is not visible in any of the specimens examined, 

 but is incurved, at the least, nearly down to the plane of the margin. 

 This valve is moderately and evenly convex, the outline on a side view 

 most strongly curved in the upper half. The cast of the interior shows a 

 straight groove commencing at the beak and extending along the middle 

 about half way to the front. This is caused by the mesial septum. The 

 dorsal valve has not been recognized. Length of the best preserved speci- 

 men 16 lines ; greatest width 18 lines. Near the west end Light-house ; 

 H. R. J. Richardson. 



Genus Trematis, Sharpe. 



T. Ottawaensis, B., Pal. Foss. vol. i, p. 53. — Macasty Bay ; H. R. 

 One specimen 12 lines wide, shows the foramen ; it is a small notch on the 

 hinge scarcely a line in depth. This proves that this species is quite 

 distinct from T. Hiironensis in which the foramen extends nearly to the 

 centre of the valve. 



Sharpe in describing T. cancellata, Sowerby, brought by Dr. Bigsby 

 from Lake Simcoe, says " the fissure in the ventral valve is small and 

 close to the hinge." It may be therefore, and indeed it seems probable, 

 that our species is identical with T. cancellata. Mr. Davidson has ex- 

 pressed the same opinion in a letter lately received from him. It would 

 however be imprudent to unite the two under one name without comparing 

 specimens with the original. 



Genus Strophomena, Rafinesque. 



S. NiTENS,B. Can. Nat. Geol., vol. 5, p. 54. — Charleton Point, Macasty 

 Bay, Enghsh Head, and many other localities ; H. R. 



S. Ceres, B. op. cit. p. 51. — Charleton Point; H. R. A species which 

 is either, identical or closely allied also occurs in the Anticosti group, and 

 is widely distributed. 



S. FLUCTUOSA, B. op. cit. p. 54. — Charleton Point and at various other 

 locaHties ; H. R. Also in the Trenton limestone at the City of Ottawa. 



S. Hecuba, B. op. cit. p. 60. — Numerous localities ; H. R. 



S. IMBREX, Pander. — Cape Robert ; H. R. 



S. suBTENTA, Conrad. — English Head ; H. R. 



S. Arethusa, B. Pal. Foss., vol. 1, p. 132. — Observation Cape ; H. R. 



