HAMILTON PERIOD. 



285 



(c.) Gasteropoda. — A few species have been described. They are all without 

 i beaked aperture, like those of older time. The Bellerophon patulus is a broad 

 species of the genus, with a flaring aperture. 



Figs. 486-493. 



Srachiopods. — Fig. 486, Atrypa aspera; 487, A. reticularis ; 488, Tropidoleptus carinatus; 

 489, Spirifer mucronatus ; 490, Athyris spiriferoides ; 491, Spirifer (Martinia) umbonatus ; 

 492, Chonetes setigera ; 493, Productus subalatus. 



(d.) Cephcdopods. — Fig. 498, Goniatites MarcellensisVan., a species sometimes 

 foot in diameter, occurring in the Marcellus shale. Two small species, the 



Figs. 4 94-497. 



Conchifers— Fig. 494, Orthonota undulata (X %)\ 495, Avicula Flabella (X %); 496, 

 Grammysia Hamiltonensis ; 497, Microdon bellistriatus. 



G. uniangularis and G. punctatus, are reported by Conrad from the Hamilton 

 beds. The genus Orthoceras is represented by a few species of moderate 

 size. 



