406 THE CANADIAN NATURALIST. [Vol. 



Vlll. 



and more convex on the posterior part of the hinge margin, is 

 probably referable to that species. 



18. Pleuromya subelliptica, Meek & Hayden. Six or seven 

 specimens of an elongated, nearly smooth Pleuromya, from the 

 Iltasyouco River, which, though very variable in shape, on 

 the whole agree tolerably well with Meek and Hayden's des- 

 cription of Myacites subellipticus from the Black Hills, much 

 better in fact than they do with the figures of that species. M. 

 subellipticus is said to be very similar in shape and sculpture to 

 Panopoza peregrina, D'Orbigny, from the Oxfordien beds of 

 Russia, and so are some of the Iltasyouco River Pleuromyce, but 

 the latter, in shape at least, are equally like some forms of P. 

 Terquemea Buvignier as figured by Agassiz under the name P. 

 tenuistriata, but in that shell the concentric striations are much 

 more numerous and regularly arranged than they are in the 

 specimens collected by Mr. Dawson. 



19. Pleuromya unionides, Roemer, Sp. Six casts of a ribbed 

 Pleuromya, (one from Sigutlat Lake, the others from the Il- 

 tasyouco River), which have been carefully compared with 

 Goldfuss' and Agassiz's descriptions and figures of the above 

 mentioned European Liassic species, and which do not appear to 

 be separable from it even as a local variety. The Sigutlat Lake 

 specimen, and three of those from the Iltasyouco River are much 

 distorted, and have their original shape much altered by pressure, 

 but two from the latter locality seem to have retained their nor- 

 mal form. Pleuromya Carlottensis, from the Queen Charlotte 

 Islands, has a shorter, higher and more ventricose shell ; its 

 beaks are more elevated and curve forwards as well as inwards ; 

 its posterior extremity, too, is more pointed. P. Carlottensis 

 is, perhaps, synonymous with P. Alduini, Bngt. (Sp.) of the 

 European Jurassic. 



20. Planorbis veternus, Meek and Hayden. While breaking 

 a large piece of the Iltasyouco River porphyrite containing a 

 valve of Gramatodon inornatus and a cast of the shell supposed 

 to be referable to Pleuromya unionides, the writer was so for- 

 tunate as to obtain a perfect specimen of this shell, in situ, in one 

 of the fragments. Planorbis veternus, and three other species 

 of fresh water shells, were first found in loose pieces of rock at 

 the base of the Black Hills in Dakota, and some doubt previously 

 existed as to the true geological horizon of these fossils. Writ- 

 ing in 1864, Mr. Meek says, ''they may possibly be Tertiary 



