ETHEBIDGE DEVONIAN ROCKS AND FOSSILS. 667 



without some notice of the class Cephalopoda, which, as a 

 group, occupies a very prominent place in the fauna of the 

 Devonian period, and one of marked significance. Pive well- 

 defined genera, all belonging to the order Tetrabranchiata, occur 

 in the British Devonian rocks. Two of these, Clymenia and 

 Cijrtoceras, have no such distinctive zoological parallel in any- 

 other British formation : they would appear to have constituted 

 two colonies of very restricted range, both in time and space ; and 

 this remark applies to either genus at the time of its culmination, 

 the one {Cyrtoceras) in the Middle Devonian of the South Devon area, 

 at Newton &c., the other {Chjmenia) in the Upper Devonian of North 

 Cornwall, at Petherwin, Landlake, &c. Whether the upper portion 

 of the Newton deposit, through synchrony or homotaxis, or both, be 

 regarded as equivalent to that of Petherwin or not*, two more 

 distinct zoological groups do not exist in any known area of the 

 British islands. The species of the genus Cj/rtocents are, with one 

 exception (C. rusticum), confined to the Middle Devonian series of 

 Newton Bushel, where twelve species are known to occur, three of 

 them (C. nodosum, C. ornatum, and C. tridecimcde) being also found 

 in the Rhenish and Eifel beds of the same age. No form is known 

 in the Ui:)per Devonian in any area; and only two, totally distinct, spe- 

 cies occur in the Carboniferous Limestone of Ireland, Derbyshire, and 

 Belgium, viz. C. Gesneri, Martin, and C. Yerneidllianum, Koninck. 

 The distribution of the genus Clymenia, which contains ten species, 

 is yet more remarkable and definite as bearing upon that of the Devo- 

 nian fauna in our own area, and clearly also identifies it with the true 

 Upper Devonian (Clymenia-limestone and Goniatite limestone and 

 shale) of the Rhenish provinces. Ten species colonize this one area, 

 and appear to have been confined to it in Britain; but through C. Ice- 

 vigata and C. striata being found in the Eifel, and C. undidata in the 

 French Devonian beds, we are enabled, aided by other characteristic 

 fossils, to associate the Upper Devonian series of Petherwin with 

 deposits of the same age on the continent. 



These two colonies of Cephalopoda, singularly distinguished by 

 two genera of the same order and numerous species in each, and 

 occupying two geographical areas, may yet have been contempora- 

 neous, and their remains synchronously deposited. Their zoological 

 associations, however, are notably different, and would point to dif- 

 ferent conditions, dependent perhaps more upon province or station 

 than time. The genus Cyrtoceras, with its thirteen species, is asso- 

 ciated with a numerous assemblage of corals and Brachiopoda in the 

 Middle Devonian of Newton Bushel ; whereas the eleven species of 

 Clymenia and three species of Goniatites, with one Nautilus, occupy 

 a marked position in the true Upper Devonian slates and limestones 

 of Petherwin and Landlake, not one of tbcse species occurring in 

 any higher beds ; and of the whole 243 known species comprising 

 the Middle Devonian fauna of South Devon, twenty-eight are com- 

 mon to it and the Petherwin beds ; these added to the twenty-seven 



* Mr. Salter believes, and with good reason, that the uppermost part of the 

 Newton beds are of the same age as the Petherwin series of North Cornwall. 



