Plate II. 



Paralegoceras iowense Meek and Worthen, Coal Measures, Iowa. 



Fig. 1, adult specimen. 



The two species of Paralegoceras figured on this plate show a transi- 

 tion from Gastrioceras to ScJiistoceras. 



Paralegoceras Newsomi Smith, Coal Measures, Arkansas. 

 Figs. 2-4, adult shell and septa. 

 Fig. 5, adolescent stage. 



ScJiistoceras Hildrethi Morton, Coal Measures, Ohio. 



Figs. 6 and 7. 



The three species of ScJiistoceras figured on this plate show a distinct 

 step toward the Arcestidae, although it is not probable that any one of 

 them was the family radicle. 



ScJiistoceras fultonense Miller and Gurley, Coal Measures, Illinois. 



Figs. 8-10. 



ScJiistoceras Hyatti Smith, Coal Measures, Texas. 



Figs. 11 and 12, adult shell and septa. 



Fig. 13, adolescent stage. 



The genera illustrated on this plate show an advance of the Glyph- 

 ioceratidae towards the Arcestidae and the Tropitidae. 



All figures on this plate are from J. P. Smith, Carboniferous Am- 

 monoids of America, Mon. XLII, U. S. Geological Survey, 1903. 



