650 



PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Nucleohranchiata. — Bellerophon andPorcellia, with perhaps ConU" 

 laria, are the only three genera known in the Middle Devonian rocks 

 of South Devon ; 3 species occur, and all are confined to that area, 

 viz. BelleropJion striatus, PorcelUa Woodwardii ?, and P. striata. 



Cephalopoda. — The species in this class are singularly distri- 

 buted through the Devonian series, and seem to have here been 

 localized in groups or colonies, the two genera Clymenia and 

 Cyrtoceras especially so. The former {Clymenia), both in Europe 

 and Britain, seems confined to the Upper Devonian, and notably so 

 with us, at Petherwin and Landlake, the genus not occurring higher 

 in the series ; and, with one exception, the species are all localized, 

 or confined to one area. Eleven species are found in the Upper 

 Devonian beds, below the Marwood group, and south of the great 

 Culm-trough. The species of the genus Cyrtoceras seem to have 

 been equally locally colonized, 12 species being confined to the 

 Middle Devonian of Newton Bushel in South Devon, C. rusticum 

 being the only form recorded as coming from the upper series at 

 Petherwin. However difficult it may be to account for this speciality 

 and colonization of a definite area by a group of MoUusca pelagic 

 in their habits, the evidence, as it is, must be received in both 

 cases, viz. of the Clymenice in the Upper Devonian, and the Cyrtocerata 

 in the Middle. The species typifying the Goniatites, Orthoceratites, 

 and Nautili are, on the other hand, as widely scattered through 

 the Devonian of North Cornwall, South Devon, and North Devon ; 

 6 species of Orthoceras occur in the Middle Devonian of South 

 Devon, and two species of each genus recur in the Carboniferous 

 beds, viz. Goniatites eoccavatus, G. serpentinus, Orthoceras cinctum, 

 and 0. undulatum. This analysis of the 235 Middle or Eifelian 

 species of South Devon will show a marked feature of close affi- 

 nity with forms occurring in beds of the same age in Rhenish Prussia, 

 the Eifel, and Erance, as a large percentage of the species common to 

 each can be adjusted to, and collated with, our Devonian types. 



Table YI. — Showing the species common to the Middle Devonian 

 rocJcs of North Devon, South Devon, and West Somerset. 



Species. 



North 

 Devon. 



South 

 Devon. 



West 

 Somerset. 



Stromatopora coneentrica, Groldf. 



•5S- 

 ■Sf- 



•St 



•5f 

 •Sf 



•5f 



•X- 







Cyathophyllum sequiseptum, M.-Edw 





coBspitosum Groldf, ■ 





helianthoides Goldf. 



obtortum, M.-Edw 



Cvstiphyllum vesiculosum, Groldf. 



Favosites cervicornis, Blainv 



fliiVfia, Tilni.vi) 





