4 i2 NORTH AMERICAN INDEX FOSSILS. 



anterior side a little more regularly curved than the posterior, and 

 by the subacute beak. 



New Scotland : New York. 



130. M.? lamellosa Hall. (Fig. 533.) Devonic. 



Both ears separated from the body of the shell by a depression. 

 Lamellose striae more or less prominent. 



Oriskany : New York-Maryland. 





^ 



Fig. 533. Megambonia? lamellosa. (Pal. N. Y., III.) 



XXXVIII. Ortonella Ulrich. 



Equivalve, very inequilateral. Beaks and umbonal ridge mod- 

 erately prominent. Surface marked with concentric striae. Hinge 

 like that of Cyrtodonta but with cardinal teeth stronger and 

 placed immediately behind the beaks. Adductor scars subequal. 

 Ordovicic. 



131. 0. hainesi S. A. Miller. (Fig. 534.) Upper Ordovicic. 



Concentric striae fine. Umbonal ridge rather strong. Type of 

 the genus. Uppermost beds of Cincinnati Group of Indiana. 



XXXIX. Vanuxemia Billings. 



Differs from Cyrtondonta in the more nearly terminal beaks, and 

 in the anterior adductor muscle scars being excavated out of 

 the hinge plate. An internal umbonal ridge is well developed. 

 Ordovicic. 



