ETHEEIDGE DEVONIAN ROCKS AND FOSSILS. 677 



this through the three genera, Goniatites, Orthoceras, and'Po^e- 

 rioceras. (See Tables IX. and X.) 



Pisces. — The 113 described species in the three recognized divi- 

 sions of the Old Eed Sandstone of England, Wales, Scotland, and 

 Ireland, until lately had no known or well- authenticated representa- 

 tives in the British marine Devonians. "\Ye now know of three 

 species : — Phyllohjns concentricus* , from the Lower Devonian slates 

 of Cornwall ; HdoptycMus, from the Upper beds of jS"orth Devon ; 

 and Coelacanthus, from the Upper beds of the Old Red Sandstone of 

 Ireland, associated with Adiantites Hibejmicus and Anoclon JuTcesii. 



We have, therefore, clearly shown in Table X. (in which are enu- 

 merated all the species known common to the two formations) that 

 fifty-six species out of the 383 known Devonian forms are common 

 to those rocks and the Carboniferous, and that forty-seven of the 383 

 are allied through the Upper Devonian beds only ; i.e. they are not 

 known to the nortli of the PickweU-Down Old Red Sandstone (Upper 

 Devonian) ; whereas twenty-eight others of the fifty-six (and of the 

 383 named in Tables I. and 11.) occur in the Middle Devonian, 

 and are found to the north of PickweU Down or elsewhere, and also 

 common to the Carboniferous ; and three only of the fifty- six (or 

 383) pass through the whole Devonian series (or connect the Carbo- 

 niferous and Lower Devonian). Two of these three I doubt ; they 

 are CyatJiocrinus pinnatus and Fenestella antiqua ; and if the Chonetes 

 sordida of the Lower or Lynton beds be that species, and not the 

 C. Hardrensis of the higher beds and also Carboniferous, we then 

 have scarcely a single species in common between the Lower and 

 Upper Devonian themselves, or between the Lower Devonian and 

 the Carboniferous. 



There are therefore fifty-six species common to the whole Devo- 

 nian formation and to the Carboniferous ; forty-seven of these fifty-six 

 are species common to the Upper Devonian and Carbouiferous ; and 

 twenty-eight of the fifty-six to the Middle and Carboniferous, and 

 three (?) to the Lower Devonian and Carboniferous. Vide Table X., 

 where the names and range of the above species are enumerated. 



YII. Steatigeaphical considerations on the Devonian Fossils, 



The many Tables which have been prepared, based upon the known 

 species and their distribution thi'ough the Lower, Middle, and 

 Upper Devonian rocks, will enable us to establish some conclusions 

 by comparing them amongst themselves as local groups, and also 

 by comparison with those of other localities. 



The chief important question arising from a critical examina- 

 tion of a set of organic remains resolves itself into the determination 

 of the horizon, age, or stratigraphical position to which they should 

 be referred. 



The rocks and their fossil contents in North Devon belong to two 

 ages, the Devonian (so called) and the Carboniferous ; and to one or 

 the other, or both, we have to refer them. 



» PengeUy, Report Roy. Geol. Soc. Cornwall, 18G0-C5. 



