PAGE. 



Figs. 46 and 47. O. (D.) SUB^QUATA var. CIRCULARIS N. H. Winchell 452 



Two views of the type specimen of Orthis circularis Winchell, a brachial and 

 profile. Trenton shales, Oxford Mills, Goodhue county, Minn. Minnesota 

 Geological Survey collection. 



Figs. 48 to 50. OKTHIS (DALMANELLA) AMCENA N. H. Winchell 453 



Dorsal, profile and cardinal views of the type specimen. V Galena limestone, 

 Spring Valley, Minn. Minnesota Geological Survey collection. 



Figs. 51 to 54. PLATYSTROPHIA BIFORATA Schlotheim, sp 455 



51 and 52. Ventral and cardinal views of a large specimen. 



53 and 54. Dorsal and profile views of a specimen of the ordinary size. Galena shales, 

 Goodhue county, Minn. Collections of W. H. Scofleld and G. Schuchert. 



Figs. 55 and 56. PLATYSTKOPHIA BIFORATA var. CRASSA James 458 



Ventral and profile views of a nearly globose specimen. Hudson Kiver group, 

 Spring Valley, Minn. Collection of C. Schuchert. 



