656 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



indeed to all that underlie the zone of Upper Old Eed Sandstone to 

 the south*. All research, as far as I know, has failed to detect a 

 single organism in these upper slates of the middle gToup; and, 

 save on the strike of the older or lower slates and limestones, which 

 I doubt not continue on to Belgium and the Rhine, we neither know 

 nor again find a single cognate species. 



7. Analysis of the British and Foreign Devonian Brachiojooda. — It 

 is difficult, amidst the conflicting opinions of distinguished naturalists 

 in this country, Europe, and America, to definitely arrive at their 

 conclusions as to the strict nomenclature of a large number of either 

 genera or species in this important class of Mollusca ; but no group 

 has played so important a part in the history of the past as the 

 Brachiopoda, and particularly in Palseozoic times. Generically and 

 specifically they are of high value in determining the age of the rocks 

 in which they occur, and notably so when we endeavour to trace 

 the history and succession of the series forming the Devonian system, 

 especially as regards the overlying Carboniferous system which at its 

 base is intimately connected with the Devonian. We have no fear 

 of confounding the Silurian with the Old Eed Sandstone or Devonian ; 

 for, except through the fishes f, one doubtful coral, viz. Favosites 

 fibrosa, one Annelide (TentacuUtes annulatus?), one Brachiopod 

 {Atrypa reticularis, and its var. aspera), one Lamellibranch (Cteno- 

 donta'i), with perhaps Orthoceras Ludense and 0. ibex among the 

 Cephalopoda (8 forms in all), there was a complete break between 

 the two, and it is thus quite clear that the 1150 known species of the 

 Silurian fauna in the British area entirely disappeared or changed 

 before any of the Marine Devonian species had existence. The accom- 

 panying Table (Table YIII.) will enable us to understand the distri- 

 bution and relations of the class Brachiopoda through the three groups 

 of the Devonian series, both in our own areas and those of the Rhine, 

 Belgium, and Prance ; and as our standard of comparison must be 

 taken from the species occupying the British area, I adjust the groups 

 amongst themselves, and compare the European species with them 

 and ultimately with the Carboniferous. There are 99 known De- 

 vonian species (see Table II. p. 616). These species are distributed 

 through 26 genera, many of which are peculiar to the Devonian age. 

 21 genera and b2 species of the 99 are common to British and 

 Foreign Devonian rocks, and are found in one or other of the three 

 divisions, or in the Lower, Middle, and Upper Devonian ; 2 species 

 only are common to, or occur in, all three divisions in our two 

 areas, viz. Athyris concentrica and Chonetes Hardrensis (0. sordida). 

 47 of the 52 species enumerated in the Table are found in our Middle 

 Devonian; and out of the total of 52 enumerated, 6 pass up to our 

 Lower Carboniferous system, viz. Chonetes Hardrensis? (O. sordida), 

 Rhynchonella acuminata, B.piignus,Productus scabriculus,Streptorhyn- 

 chus crenistria, and Strophomena rhomboidalis. This is in accordance 

 with what we should expect in the conformable and succeeding system, 

 where no stratigraphical break is known to exist ; none, however, of 



* The Pickwell-Down Sandstones. 



t The fishes on the confines of the Silurian and Old Red being chiefly con- 

 fined to the Passage series, 4 genera and 7 species occmu-ing. 



