GENERA OF AMERICAN AMMONOIDS. 



TcthJi' of J\iJeiiZ(>lf 1/ III monoid (jinera—QonimweA. 



25 



AMMONOIDS OF THE AMERICAN CARBONIFEROUS. 



GENERA REPRESENTED. 



The writer has made no distinction between goniatites and ammonites, 

 because there is none that will hold. Certain families, or genetic series, 

 contain some genera that, on account of simplicity of the septa, would be 

 called goniatites, and others that might approjiriately be termed ammonites. 

 There are other forms that, while having simple or goniatitic septa, have 

 forward-pointing siphonal collars and would thus fall under the definition 

 of anniionites. The form of the aperture has been frequently used as a 

 mark of distinction between these two groups, but this is so commonly 

 unknown as to have little value in systematic work. 



There are at present known in the American Carboniferous eleven 

 families, twenty-four genera, and eighty-nine species of anunonoids, 

 besides two apocryphal species (not ammonoids). Their stratigraphic 

 occurrence is as follows : 



Kinderhook: Prolecanites, Prndromites, Aganides, Prionoceranf , Muensteroceras, Gonioloboceras.^, 

 Pericyclus, Agoniatites. 



Osage: Aganides?, Muensteroceras.'. 



