6o6 



NORTH AMERICAN INDEX FOSSILS. 



10. A. deleta (Sardeson). (Fig. 805, c-e.) Ordovicic. 

 Small, elliptical, smooth, apex a short distance from front, 



incurved. 



Black River of Minnesota. 



11. A. patelliformis (Hall). Ordovicic. 

 Small, slightly narrower anteriorly, beak projecting to margin 



of shell ; growth lines sublamellose. 

 Trenton of New York. 



12. A. simulatrix Ulrich and Scofield. (Fig. 805,/, i.) 



Ordovicic. 

 Small, widest anteriorly ; beak slightly projecting anteriorly. 

 Black River of Minnesota. Trenton of Kentucky. 



13. A. cingulata Ulrich. (Fig. 805, £-, /z.) Ordovicic. 

 Large ; beak strongly incurved and projecting slightly beyond 



the somewhat broader anterior end. Growth lines sublamellose. 

 Trenton of Kentucky. 



V. Pal^eacivlea Hall and Whitfield. 



Patelliform, circular or elliptical shells with subcentral apex and 

 broad concentric wrinkles marking the surface. Cambric-Ordo- 

 vicic. 

 14. P. (Parmophorella) acadica (Hartt). (Fig. 809, c) Cambric. 



When uncompressed, oval in outline, with beak one third or one 

 fourth distant from the end. Concentric wrinkles weaker on 



Fig. 806. Archinacella de- 

 formata. (After Raymond. ) 



Fig. 807. Palceacmcea typica. (After Hall & 

 Whitf., 23d N. Y. Mus. Rep.) 



shorter end. When depressed, beak appears subcentral as in the 

 figure. 



St. John formation of New Brunswick (Div. 1, c) and Hay ward 

 argillutytes of Braintree, Mass. 

 15. P. typica Hall and Whitfield. (Fig. 807.) Cambric. 



