(5n CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



Unio Dewetanus, Meek & Hayden. 



Vi-iio Dciroiamis, Meek & Hayden. 1857. Proc. Ac. Kat. Sc. Phil, vol. IX., p. 145. 



" ' Sleek. 18(37. Rep. U. S. Geol. Surv. Terr., vol IX., p. 519, pi. 41, 



flgs. 2, a, b, c. Illustrated also on pi- 17 (figs. 4 and 5) of Dr. C. 



A. White's Rev. Non-Marine Poss. Moll. N. Am. Washington, 



1883. 



South Saskatchewan, one mile below^ the mouth of the Bow Eiver, 

 T. C. Weston, 1883 ; a few rather imperfect specimens. 



As ah-eady stated on page G, Dr. C. A. "White is of the opinion that 

 C Deweymms is only a variety of U. Daiuv. 



U.N'IO SUPRAGIBBOSUS. (N. Sp.) 

 Plate 10, fig. 1. 



Shell com])i-essed at the sides, the maximum convexity being appar- 

 ently less than half the greatest height, though all the specimens bo far 

 f ollected are more or less crushed laterallj-, — rather tumid a little behind 

 the mid-length and below the middle in some individuals, so that the 

 i.(ntline of a section through the centre of the closed valves at a right 

 angle to their length would be very nearlj^ lenticular : a little longer 

 than high, and very inequilateral : lateral outline obliquely and broadlj- 

 subovate : superior border gibbous behind the beaks : fiosterior end of 

 the base always somewhat pointed. Anterior side ver}' short, its margin 

 abruptly and more or less broadly rounded or receding obliquely and 

 al.iruptljrinwai'ds and downwards from a little above the middle into the 

 base below: posterior side much longer than the anterior, its extremity 

 obliqucl}' tnuicatod above and in the middle and narrowly rounded or 

 bluntly pointed at the base below. Superior border broadly and con- 

 vexly arched behind the beaks and probably winged when quite perfect : 

 ventral margin broadly scmiovate, usually much straighter behind than 

 in front : umbonal region not distinctly detined as such and flattened 

 laterallj-; beaks small, inconspicuous, depressed considerably below 

 the highest level of the superioi- boi-der, and placed very near the 

 anterior end but not quite terminal. 



Sui-fi.u-e concentrically striated. Hinge dentition and muscular 

 impressions unknown. 



Dimensions of the most pei'fect specimen collected . maximum length, 

 sixty millinletres : greatest height of the same, about forty^-six mm.: 

 appi-oximato thickness through the closed valves, about twenty mm. 



