THE DEVONIAN PERIOD. 463 



it is probable that they had been living for some time in the sea in 

 the originating tract of the Onondaga fauna somewhere in the northern 

 region. It is not impossible that fish were inhabitants of the northern 

 seas from the late Silurian on, but not of the more southerly seas pre- 

 vious to the time of this invasion, since their relics are absent from 

 the preceding Helderberg and Oriskany formations. Several of the 

 genera of the arthrodirans and sharks have been found in the deposits 

 of Germany (Dinichthys, Macropetalichthys, M achcer acanthus) , implying 

 that they lived in the interior sea of Europe as well as that of America. 



Fig. 209.— Diagrammatic front view of the dentition of Dinichthys herzeri, Huron 

 shales, Delaware, O. (After Newberry.) 



Others (Acanthaspis and Onychodus) have been recognized in the 

 Lower Devonian deposits of Spitzbergen, directly supporting the 

 suggestion of a northerly distribution. 



The profusion of corals. — Another significant feature of the Onon- 

 daga fauna was the extreme abundance of corals. From the rapids 

 of the Ohio at Louisville there have been collected more than two 

 hundred species deemed worthy of illustration. Other localities add 

 greatly to the total list. These embrace both the simple cup form 

 (Fig. 208, b) and the compound type. Some of the former reached 

 extraordinary sizes, as in the case of Zaphrentis gigantea, individuals 

 of which sometimes attained a length of eighteen inches and a diam- 

 eter of three inches. The general range in size was wide, small and 

 large being intermingled, though the large preponderated. The salient 

 expression of the epoch, however, lay not so much in the advance of 



dumosum Con., a capulid shell with large, hollow spines. Pelecypoda: i, Conocardium 

 trigonale Hall, a dorsal view of a common Onondaga pelecypod. The genus occurs 

 in the Silurian and also in the Mississippian. Echinodermata: j, Nucleocrinus 

 verneuili (Troost), a blastoid which occurs in great numbers in one layer of the 

 Onondaga limestone in the Ohio valley. Trilobita: k, Odontocephalus cegeria 

 (Hall), one of the dalmanites, showing the development of ornamentation on the 

 border of the head and tail. Cephalopoda: I, Tornoceras mithrax (Hall). This is 

 the first goniatite to appear in the faunas of America. The goniatites are dis- 

 tinguished from earlier representatives of the cephalopods by their lobed sutures. 

 (Weller.) 



