580 



GEOLOGY 



were abruptly bent, and suture lines which were lobed (i, Goniatites, 

 Fig. 416). This was the first notable step in a remarkable series of 

 crumplings of the septa which developed later. Gastropods, similar 

 to those of the earlier Devonian faunas, were present and the spines 



Fig. 416. Onondagan Fossils: a, Zaphrentis ponderosa Hall, a medium- 

 sized, simple horn coral; b, Nucleocrinus verneuili (Troost), a blas- 

 toid abundant in one layer of the Onondagan limestone in the Ohio 

 valley; c-h, brachiopods: c, Stropheodonta concava Hall; d and e, Pro- 

 ductella spinulicosta Hall, an early representative of a genus which 

 became abundant in the Upper Devonian, and gave rise to the typical 

 productus of the Mississippian and Pennsylvaman faunas; /, Spirifer 

 acuminatus (Con.), a characteristic Onondagan brachiopod; g and h, 

 Crytina hamiltonensis Hall, two views of a species having a wide geo- 

 graphic distribution and a great geologic range in the Middle and I'pper 

 Devonian; i, Tornoceras mithrax (Hall), the first goniatite in AmenV:i. 

 The goniatites are distinguished from earlier cephalopods by their lobed 

 sutures; /, Conocardium trigonaie Hall, a dorsal view of a common Onon- 

 dagan pelecypod; k, Platyceras dumosum Con., a capulid gastropod 

 with large hollow spines; I, Odontocephalus cegeria (Hall), a trilobite 

 showing ornamentation of the border of the head and tail. 



of the shells had now become pronounced among the capulids, which 

 perhaps signifies the necessity of defense against the abundant 

 fishes and cephalopods. Peleci/pods were also abundant, and many 

 of them resembled those of the Helderberg and Oriskany faunas, 



