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PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



true Carboniferous Limestone, the two together would represent 80 

 genera and 170 species, 17 genera and 22 species being peculiar to 

 the Lower Limestone Shales. No one can doubt that these dark, 

 impure, argillaceous limestones were the commencement of the purer 

 calcareous series above ; and palaeontologieally they cannot be sepa- 

 rated. Closer research will probably show that the 17 genera now 

 known to occur only in the Lower Limestones exist in the succeed- 

 ing series. 



Carboniferous Limestone. — This finely developed group of rocks 

 in the British Islands, which has received so much attention both 

 under geological and palseontological aspects, is possibly better 

 understood than any other division of the Carboniferous system. 

 The limestone beds known as the Mountain Limestone have yielded 

 no less than 63 genera and 147 species of fishes ; but the Yoredale 

 series which succeed them yield none ; and only 3 genera and 3 species 

 are known in the Millstone Grit (Megalichihys Hibberti, Ehizodus 

 Hibberti, and Acanthodes Bronni). This sudden cessation or non- 

 occurrence can scarcely be accounted for on lithological grounds, or 

 original sedimentary accumulation, such as would be applicable to 

 the habits of certain genera of the Mollusca. Bathymetrical con- 

 ditions may have influenced this paucity in the whole fauna of the 

 Yoredale and Millstone Grit, which is so apparent on inspection of 

 the Table of Distribution. 38 genera of Placoidei are confined to 

 the Carboniferous Limestone ; and 12 genera of the same order are 

 from both Lower Limestone Shale and Carboniferous Limestone : on 

 the other hand, it is remarkable that only 6 genera of Ganoidei are 

 strictly or essentially confined to that horizon ; they are Acrolepis, 

 Asterolepis, Coccosteus ?, Cycloptychius, Phyllolepis, and Platycanthus. 

 (I give them as near the truth as possible, as the species of Ganoidei in 

 the Carboniferous system are in as much confusion as the Placoidei*.) 

 As before stated, the Yoredale rocks (Upper Limestone Shale of some 

 areas) have not yielded remains of fishes. We are in doubt as to the 

 real position of the Upper Limestones of Durham and Northum- 

 berland, or what, if any, should be assigned to the Yoredale group. 

 Nevertheless I am not aware of any Vertebrata occurring in the 

 Yoredale beds. The Millstone Grit, as before stated, has only (so 

 far as I know) yielded 3 genera and 3 species, and these in the 

 form of scales. 



Lower Coal-measures. — Whatever conditions caused so complete 

 a break in the distribution of the fishes in our area zoologically, 

 stratigraphically, and geographically during the deposition of the 

 rocks mentioned, the return of the same genera and many of the 

 same species in the Lower Coal-measures is equally important. We 

 have evidence of the remains of 52 genera and 112 species, the 

 whole composed nearly equally of the orders Placoidei and Ga- 

 noidei. The numbers may be thus expressed : — In the Lower Coal- 



* The Ganoid Fishes are under revision by Dr. Traquair, whose accurate 

 knowledge of the order will be brought to bear upon their structure and classi- 

 fication. 



