ETHEEIDGE DEVONIAN BOCKS AND POSSILS. G59 



8. Devonian and Carhoniferous Bracliiopoda. — It has been before 

 stated that 99 species of this class are in the Devonian rocks of 

 Britain. Table II. shows every species in Xorth Devon, arranged in 

 the order of time or succession. Those species occurring in South 

 Devon and Cornwall are compared with them ; in other words, every 

 species in Xorth Devon is collated with the same in Cornwall and 

 South Devon. Of the 99 known forms, we have, then, in the Xorthern 

 area b2 common ; and of 2Q genera known in British Devonian rocks 

 22 occur in Xorth Devon, 5 only, viz. Camaroplioria, Davidsonia, 

 Leptcena, Pentamerus, and JRetzia, being required to complete the 

 generic equivalence of the two areas. This Table also shows that 

 27 of the 4S Xorth-Devon species also occur in the foreign Con- 

 tinental rocks, and that 13 are common to the Carboniferous above ; 

 but these are related chieflv, as will be seen, through the passage- 

 scries (vide Table YIII. p. 658, and Table IX. p. 669). 



We will now see how far the species occurring in the Lower De- 

 vonian (Lowest or Lynton) beds agree 'uith those of the Upper and of 

 the Carboniferous south of PickweU Down at Baggy, Garwood, Sloly, 

 and Pilton — the two groups of rocks which Mr. Jukes states are on 

 the same geological and paleeontological horizons, and that both are 

 the " Carboniferous Slates " of Ireland. In this comparison I 

 neglect aU but the Brachiopoda. The mass of species in other 

 classes and orders will be compared hereafter in their proper place. 

 The species occurring in the Lyuton Slates are the following : — 



South of TicJcinell. 

 Chonetes Hardrensis, Thill. 



Lynton. 

 Athyris concentrica, V. Buch. 

 Chonetes sordida, Soxc. (velC. Hardrensis ?, PhilL). 

 Spirifera canalifera, Valen. 



hysterica, Schloth. 



lajvicosta, Valen. 



Orthis granulosa, PhilL 



arcuata, Phill. 



Streptorhynclius unibraculum, Schloth. 



The only species, therefore, believed to be common is the Chonetes 

 Hardrensis ; and there is much doubt still as to the Lynton, C. (Lej).) 

 sordida, Sow., being the Upper Devonian and Carboniferous Chonetes 

 Hardrensis of Phillips. It is, however, retained. Should they on 

 closer research prove to be distinct, we then have no sjyecies in'this 

 or any class common to the Lower Devonian slates of the Lynton area 

 and the Upper Devonian, or to the Carboniferous Slates, ^or to the 

 Lower Limestone shales, anywhere. Casts of Crinoidea cannot be 

 received as of specific value ; and the dubious FenesteUa antiqua, said 

 to be in eveiy bed, has yet to be understood. However much, then, 

 at a casual glance, the slates and grits of Lynton may be said to 

 physically resemble the beds of Baggy, Marwood, Croyde, Braun- 

 ton, and Pilton ifec, on close inspection and zoological analysis, 

 they bear scarcely any resemblance. The physical conditions, 

 structure, arrangement, and cleavage of the Lpiton Slate group 

 generally, altogether differ from the associated slates, brown 

 sandy grits, and limestones in the Baggy and Croyde area — to say 



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