10 CONTRIBUTIONS TO CANADIAN PALiEGNTOLOGT. 



Antei-ioi- side veiy short, obliquely and convexlj' subtruncated at its 

 extremity above and in the middle, but obtusely sub-angular below at 

 its junction with the ventral margin : posterior side elongated and pro- 

 duced into a long and narrow pointed beak, which is either straight or 

 curved slightly upwards and whose upper margin is strongly angulated. 

 Ventral margin semi-ovate, very moderately convex, curving up- 

 wards somewhat more rapidly at the anterior than at the posterior end, 

 but very gently at both, the posterior half being often nearly straight 

 or even faintly concave : superior border descending abruptly and 

 obliquely in front of the beaks and confluent with the margin of the 

 anterior end in one unbroken line which descends oblicj^ucly from the 

 heaks to the base, — descending gradually behind the beaks in either a 

 straight line or with a shallowly concave curve to the upper termina- 

 tion of the posterior side : beaks obliquely flattened on all sides, placed 

 in advance of the middle, that of the right valve carved inwards and 

 downwards, that of the left erect but somewhat incurved and with a 

 slight forward inclination. Posterior area large and very distinctly 

 defined, flattened at a right angle to the valves and in some cases 

 shallow.lj' excavated, broadlj' lanceolate in outline as viewed from 

 above, and bordered by the strong keel which also forms the upper 

 margin of the beaked posterior extremity' of each valve. 



Surface markei.l with a few coarse and rather distant but irregulai-ly 

 disposed lines of growth, with much finer and close set concentric 

 strite between them. Tost rathei' thick : hinge teeth as in Corbula 

 proper, muscular impressions unknown. 



Dimensions of a full sized and perfect specimen : length, forty 

 millimetres : maximum height, twenty-five millimeti'cs : thickness 

 through the closed valves, nineteen millimetres. The maximum 

 thickness of another specimen of the same length and height is only 

 sixteen millimetres. 



In young individuals the anterior end of the shell is regularly 

 rounded, and the po-terior ai-ea is not so much flattened down as it is 

 in the young shell. Th..' beaked posterior side is usually pointed at its 

 extremity, but in some specimen- there i- a distinct truncation at its 

 extreme tip). 



Eye-Gras- flat. Old Man Eiver, G. 51. Dawson, ISSl and T. C. We-ton. 

 1S83. extremely abundant. ITppor Belly Eiver, twenty-three miles 

 above the mouth of the "Waterton, and Scabby Butte," seven miles 

 north of the confluence of the Belly and Old Man Eiver- : E. G. 

 MeConnell, ISSl. All from the Si. Mary E. Series. 



A very distinct species, apparently belonging to the same section of 

 the genus as the Corhula pyrifonnis of Meek. Sjiecimens of the la iter 

 -shell from the Bear Eivei- Laramie of S. TV. Wvemiino-. kindly for- 



