442 Silurian and Devonian Fossils of Canada. 



times less. Usually, it is transversely broad-oval ; the apex of the 

 dorsal valve obtusely angular, and that of the ventral rather acute. 

 The dorsal valve is moderately and pretty uniformly convex ; the 

 ventral valve depressed-convex. The beak of the ventral valve 

 projects about two lines above that of the dorsal valve, and ex- 

 hibits a wide, scarcely concave area, with a triangular excavation 

 representing the obsolete foramen ; the surface is smooth, or with 

 a few concentric imbricating furrows of growth. In' the inside of 

 the dorsal valve there are near, but above the centre, two pyri- 

 form muscular impressions, with their pointed extremities close 

 together and directed downwards, while in the upward direction 

 they diverge outwards; they are separated by an obscure round- 

 ed ridge, and surrounded on the lower side by an elevated angular 

 border, which forms a projecting point just below their lower ex- 

 tremities. Beneath and close to the hinge there is a narrow and 

 deep fiexuous furrow. The muscular impression at the cardinal 

 angles figured by Davidson in 0. Apollinis (Eichwald), 0. trans- 

 versa (Salter), and 0. Davidsoni (Salter), are very indistinct in 

 this species ; the area of the ventral valve does not appear to be 

 striated. The interior of the ventral valve is not clearly shewn in 

 any of our specimens. Width usually about two inches, but some 

 of the fragments undoubtedly belonged to individuals which were 

 three inches wide. The length from the beaks to the base, is ei- 

 ther equal to or a little greater or less than the width, the dimen- 

 tions being variable. 



Locality and Formation. — Occurs abundantly at the Fourth 

 Chute of the Bonne-chere, Pauquette's Rapids, and in the Town- 

 ships of Stafford and Westmeath, County of Renfrew, associated 

 with fossils of the Trenton and Black River limestones. 



Collectors. — Sir W. E. Logan, J. Richardson, and E. Billings. 



Genus Eichwaldia (Billings.) 



Generic Characters. — Large valve perforated on the umbo for 

 the passage of the peduncle ; the place of the foramen beneath 

 the beak occupied by an imperforate concave plate ; the interior 

 divided by an obscure medio-longitudinal ridge ; interior of 

 smaller valves divided throughout from the back to the front by a 

 very prominent medio-longitudinal ridge ; no hinge, teeth, 

 sockets, or other articulating apparatus in either valve. 



After a great deal of examination and comparison I have not 



