90 NEW YORK STATE MUSEUM 



£rac7iiopods. Rhipidomella, which culminates in the Meso- 

 devonic, is largely represented. But a few doubtful representatives 

 are known in the Silunc. 



Schizophoria, eminently characteristic of the higher Devonic, 

 is clearly defined in the Helderbergiun. The only earlier species of 

 the genus is generically inchoate. Orthothetes is in the line of 

 progress from its elementary forms in the Niagara to its abundant 

 development in the middle and upper Devonic. It is represented by 

 two species, O. deformis and O. woolworthana. 



Leptostrophia, beginning its development here becomes a 

 large and characteristic Devonic group. 



Brachyprion, well advanced in structure toward the type of 

 Stropheodonta, is represented by two species. Progress along the 

 same line continues in the Oriskany and thereafter the type seems to 

 lose itself in the latter genus. 



Strophonella, starting in the Silunc, attains its culmination 

 in the Helderbergian (S. headleyana H., S. leaven worthana 

 H., etc., and gradually declines to the close of the Devonic. 



Leptaenisca is not known elsewhere in American faunas. 



Chonostrophia is known only in the Helderbergian, Oriskany 

 and Onondaga. 



Spirifer. The lamellose septati, represented by Sp. perlamel- 

 1 o s u s , become culminant in later Devonic faunas. 



The same is true of the Fimbriati unicispinei, (S. saffordi, 

 S. cyclopterus, S. octocostatus) which are preceded by an 

 inceptive representation in the Niagara and followed by several species 

 in the Devonic. 



Of the Aperturati the only species is S. concinnus, the 

 earliest representative of the S. orestes subtype. This entire group 

 becomes culminant in the Devonic and lower Carbonic. 



The genus Merista is known in America only in the Helder- 

 bergian and Oriskany faunas. 



Meristella has a remarkable development in this fauna and its 

 existence is continued through the Mesodevonic. It is not known in 

 the Siluric. 



