PLATE XXIII. 



Pteria (Oxttojia) Cornueliana (page 166). 



l-'igure 1. Side view of a large and nearly perfect left valve, from the Rocky 

 Mountains three miles north of the east end of Devil's Lake. 

 Figure la- An imperfect right valve from the same locality. 

 I'igure 1 h. Outline of another left valve from the same locality. 



SOHLCENBACHIA GRACILIS (pflge 1*71). 



Figure 2. Side view of the type of this species. 



Figure -". Outline of the aperture of the same specimen. The unbroken line 

 shews the breadth of the aperture at the summit of one of the 

 ribs, and the dotted line the thickness of the shell in the 

 interval between two of the ribs. 



