HAMILTON PERIOD. 



285 



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

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

 species of the genus, with a flaring aperture. • 



Fiss. 486-493. 



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

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

 492, Chonetes setigera ; 493, Productus subalatus. 



(d.) Cephalopods. — Fig, 498, Goniatites Mareellensis Van., a species sometimes 

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



Figs. 494-497. 



Coxchifers— Fig. 494, Orthonota undulata (X %)•- 495, Avicula Flabella (X K); 

 Grammysia Hamiltonensis : 497, Microdon bellistriatus. 



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

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



