598 



HISTORICAL GEOLOGY. 



904 to 911 represent the most common kinds. The broad-winged species, 

 Fig. 907, Spirifer pennatus, was one of the most abundant. 



904-911. 



MP 



Beaohiopods. — Fig. 904, AtryiKi aspera; 905, A. reticularis; 906, Tropidoleptus carinatus ; 907, Spirifer 

 pennatus ; 908, Athyris spiriferoides ; 909, Ambocoelia umbonata ; 910, Chonetes setigerus ; 911, Product- 

 ella subalata. Figs. 904, 906-908, Meek ; 905, 909-911, Hall. 



5. Mollusks. — In the shaly sandstones of this period Lamellibranchs 

 abound. 21 species have been described by Hall from the Marcellus beds, 

 and 174 from the Hamilton, only one being common to the two. But in 

 Ohio and farther west, where the beds are calcareous, they are few in num- 

 ber. Only 10 New York species occur at the Falls of the Ohio. The follow- 

 ing figures, 912-916, show some of the characteristic species. The Gastro- 



CoNCHiFERS. — Fig. 912, Ortlionota undulata (.x|); 913, Pterinea flabella(x|); 914, Grammysia bisulcata ; 915, 

 Microdon (CypricardeUa) beUistriatus ; 916, StyUoUna fissureUa. Fig. 912, 916, HaU; 913, 915, Conrad ; 914, 

 deVerneuU. 



pods were mostly of the same genera as in the earlier Devonian: Platyceras 

 (many species), Platystoma, Trochonema, Pleurotomaria (many), Euom- 



