THE CARBONIFEROUS PERIODS 



483 



Fig. 456. — Carboniferous pelecypods : A> Grammysia hannibalensis (Mississip- 

 pian) ; B, Pleurophorus tropidophorus (Pennsylvanian) ; C, Allorisma terminate (Penn- 

 sylvanian) ; D, Aviculopecten occidentalis (Pennsylvanian) ; E, Myalina recurvirostris 

 (Pennsylvanian) ; F, Monopteria longispina (Pennsylvanian.) 



of subsequent periods ; that is, they were simple in structure and 

 united characteristic features of two or more distinct groups, and 

 were therefore probably the ancestors of those insects whose char- 

 acters they combine. One extinct order (Paleodictyoptera, old, 

 netted wing) is especially interesting because it is believed to be 

 the stock from which all insects were descended. Carboniferous 



Fig. 457. — Carboniferous cephalopods : A, Medlicottia copei; B, Aganides rota- 

 torius; C, Waagenoceras cumminsi; D, Temnocheilus forbesianus ; E, Muensteroceras 

 oweni. 



