OSTEAGODA. 693 



Krausella arcuata.l 



ventral portion is much less prominent. Of all these differences the most striking 

 and perhaps the only important one is the last. 



Bairdia, or as it should now be called, Krausella anticostiensis Jones, sp., is 

 represented as having a much blunter anterior outline, but in the Cincinnati forma- 

 tion of Ohio and Indiana we have a species that comes much nearer, the anterior 

 end of the right valve being quite as narrow, only the most prominent point is 

 higher. 



Formation and locality. — Lower third of the Trenton shales, Minneapolis, Minnesota; lower Trenton 

 limestone, Mineral Point, Wisconsin, and Dixon, Illinois; Birdseye limestone. High Bridge, Kentucky. 



