512 



NORTH AMERICAN INDEX FOSSILS. 



Trenton : New York, Canada. Middle Galena : Wisconsin, 

 Minnesota. 

 408. M. concentrica Hall and Whitfield. (Fig. 686, a.) 



Ordovicic. 



Surface marked by regular concentric furrows which become 

 obsolete on the umbonal ridge. 



Cincinnati : Ohio, Indiana, Kentucky. 



Fig. 687. Modiolopsis modiolaris. (After Logan. ) 



409. M. modiolaris (Conrad). (Figs. 687 and 688.) Ordovicic. 



Shell narrowed anteriorly, obliquely truncate posteriorly. Beak 

 not prominent. Surface crossed by concentric undulations. 



Lorraine : New York, Pennsylvania. Cincinnati region. 



Fig. 688. Modiolopsis modiolaris, internal mold. (Pal. O., II.) 



410. M. Orthonota (Conrad). (Fig. 689.) Siluric. 

 Subquadrangular, surface marked with concentric lines only. 

 Medina : New York. 



411. M. primigenia (Conrad). (Fig. 690.) Siluric. 

 Posterior end with ear. Surface marked with strong concentric 



striae and very faint radiating ones. 

 Medina : New York. 



