35 



NORTH AMERICAN INDEX FOSSILS. 



centric growth lines. Length equalling or greater than the 

 width. 



Niagaran of Ohio, Tennessee, Kentucky, Indiana, Illinois, Wis- 

 consin. 



CXXI. Athyris McCoy (emend. Hall and Clarke). 

 Subequally biconvex, varying in outline from subcircular to 

 transversely elliptical. Beak of pedicle valve incurved, perforated 

 bya'round foramen which encroaches upon the umbo. Surface 



medially sinuate. Teeth prom- 

 inent and recurved at the tips, 

 supported by stout dental 

 lamellae. Brachial valve with 

 broad and deep dental sockets 

 and strong hinge plate; the 

 large muscular areas well de- 

 fined. Spirals laterally di- 

 rected, with a large saddle shaped jugum, the anterior portion of 

 which divides, each branch uniting again with the primary lamella. 

 Siluric-Mississippic. 



411. A. fultonensis (Swallow). (Fig. 460.) Devonic. 



Differs from A. angelica in its subquadrate form and somewhat 



KlG. 460. Athyris fultonensis ( Ind. Geol 

 Survey). 



Fig. 461. Athyris spiriferoides (Pal. N. Y., IV. 



