609 



one in the sinus ; 3 S, ventral view ; 3 (?, front view, showing 

 prominent mesial fold and deep sinus ; 3 d^ ventral view of 

 another specimen with a second smaller plication in sinus, and 

 a third on the fold. Hudson river ( Cincin.) formation^ IIIl). 



Orthis (Platystrophia) biforcata, Var. laticosta, James. 



Pal. Ohio, Yol. 1, 1873, p. 116, pi. 10, figs. 4 a, back; 5, belly 

 valve; <?,- front, showing prominent mesial fold in the wide? 

 deep bay (sinus) ; d^ inside of belly valve; e^ inside of back 

 valve, showing the obscure muscular scars, very small linear 

 cardinal process, and the tooth-like brachial processes ; /', mag- 

 niiied granular surface. — Cincinnati^ Illi, 



Orthis biforata (Platystrophia) Var. lynx. Von Buch. 



Pal. Ohio, I. 114, pi. 10, 

 fig. 1 a^ back of medium- 

 sized adult shell ; 1 5, 

 front of same (should 

 be turned upside down) ; 

 1 c, ventral of same; 1 

 d. hinge, double area, 



