160 WELLBURN : FISH FAUNA OF YORKSHIRE COAL MEASURES. 
With the exception of the Cannel Coal at Tingley — where 
the fish remains are found, not only in the shale or " Hubb," but 
also in the coal itself — the remains are found in the shale imme- 
diately above the coal seams, being most plentiful in the shale 
lying directly on the coal. 
Habits of Life. — When we come to consider under what 
conditions the fish lived, and their habits during the deposition of 
the Coal Measures, we are faced with a rather difficult problem, 
as we find Elasmobranchs, Teleostians, and in some districts even 
Dipnoian fishes mingled together in such a manner as to point 
to the fact that they must have been associated during life- 
Representatives of the Elasmobranchs are found not only above 
the Halifax Hard Bed Coal, which is undoubtedly of marine 
origin, but also in most of the beds higher in the measures, where 
the coal seams appear to have been formed under fresh water condi- 
tions. The ChondroafAan 7'e/^6os^m7is— represented by the families 
PalseoniscidiB and Platysomidfe — are also found in beds of both 
fresh water and marine origin, this going to prove that they — 
like their living representative, the Sturgeon — ^were able to exist 
under both these conditions ; but when we come to the Dipnoi 
— fishes which are represented in the Yorkshire Coal Measures 
by the family Ctenodontidie — their remains have hitherto only 
occurred in beds of undoubted fresh water origin. Again, the 
Crossopteri/gidian Teleostian genera, Megolichthys and Codacanthus 
— whose living representative Polypterus is at present found living 
in the rivers of Africa — are found in all the fish-bearing coal 
shales in both the Middle and Lower Measures — i.e., in beds of 
marine and fresh water origin. These facts may, I think, be 
explained by the supposition that the lakes or lagoons, in which 
the coals of the Middle and the greater majority of the seams of 
the Lower Measures were laid down, were at one time in direct 
communication with the sea, but that subsequently, owing to some 
elevation of the land or some other cause, they became shut off 
from the sea, this producing salt water lakes containing fish of a 
marine type. Then it seems reasonable to suppose that the water, 
being fed by rivers and streams from the land, would become 
