612 



HISTORICAL GEOLOGY. 



Bracliiopods were far more numerous in the Chemung beds than in the 

 Portage. The figures 939 to 942 represent common species ; 941, an Atrypa 

 of ornate type, lilce the young of A. reticularis ; 940, a species of Productella. 



933-938. 



93?.. 



934. 



936. 



937. 



Beachiopods. — Fig. 933, Spirifer IfevisCP.) ; 934, Leiorhyncus quadricostatuin (G.) ; 935, Lingula spatulata, (x 3) 

 (G.): 936, Orbiculoidea Lodensis, (x 2)(G.). La.mellibranchs. — Fig. 987, Lunulicardium fragile (G. and P.); 

 988, Glyptocardia speciosa (G. and P.). Hall, except Fig. 934, King. 



4. Mollusks. — Lamellibranchs were few in the Portage, but very numerous 

 in the xsew York and Pennsylvania Chemung beds, outnumbering all other 

 Mollusks. Hall describes 252 Chemung species, and only 11 from the 

 Portage and Genesee beds, Avith 174 from the Hamilton. Figs. 939, 940, 

 943, 944, 945, represent some common forms. A compressed specimen of a 

 New York Catskill species is represented iu Fig. 948. It has the form of a 

 freshwater Unio, and the name Amnigenia, of Hall, alludes to its suspected 

 freshwater habitat. It is from the " Oneonta sandstone " of Chenango and 

 Otsego counties, IST.Y., and has been found also in the Catskill beds of Bedford 

 Countj^, Pa. 



The '' Black shale " of Ohio and the states west and south, which repre- 

 sents the G-enesee with more or less of the Portage and Chemung beds, is 

 remarkable for the great rarity of fossils. In Ohio the lower beds have 

 afforded the Portage species : CJionetes scitulus, Goniatites complanatus, Coleo- 

 lus acicida, StyUolina fissurella ; and the upper and middle portion, the 

 Chemung species: Leiorhynchus mesacostale, Spirifer clisjunctus, S. alius; 

 also species of Lingula and Orbiculoidea. Southern Indiana has afforded 

 Lingida spatulata, Discina (Schizobolus) truncata, Ghonetes lepidus, Leiorhyn- 

 chus quadricostatum (Genesee species), L. limitare (a Marcellus sp.), StyUolina 

 fissurella. Fossil plants also are rare ; but wood of Gymnosperms, referred 

 to Dadoxylon and Cordaites, is found in it. In most parts of the shale, 

 Sporangites are in great abundance, S. Huronensis of Dawson, -^-I-q to y^^ 

 inch in diameter. 



Gastropods are few in both the Portage and Chemung beds. The prolific 

 genera of the earlier Devonian, Platyceras and Platystoma, have a number 



