DAVIS : OSTRACACANTHUS DILATATUS. 
191 
OSTRACACANTHUS DILATATUS (GEN. ET SPEC. NOV.), A FOSSIL 
FISH FROM THE COAL MEASURES SOUTH OF HALIFAX, 
YORKSHIRE.* BY JAMES W. DAVIS, F.G.S., &c. 
The fossil remains of a fish, which I introduce in this paper, 
were found in a bed of cannel or stone coal, occurring south- 
west from Halifax in this county. The coal is extensively 
wrought, and occupies what appears to have been a number 
of depressions on the surface of the land during carboniferous 
times. The beds of coal are found to be thickest in the 
centre, and, thinning off in every direction, disappear in 
the course of a few miles. There were probably several of 
these lagoon-like depressions, and they are known to have 
extended over twelve to sixteen square miles. f In some 
cases the coal is found to contain a large number of fossil 
fish; but this is by no means universally the case. In far 
the greater majority of the districts worked, the fish 
remains are extremely rare. I have however obtained from 
the bed from which this ichthyodorulite was got the remains 
of both ganoids and sharks, including Megalichthys, Rhizo- 
dopsis, Coelacanthus, and Gtenodus. Spines of Gryracanthus 
Ctenacanthus, and a series of Pleuracanthus and Orthacan- 
thus, including some new species which demonstrate that 
the two genera ought to be united and also include with 
them the teeth Diplodus. Teeth of Helodus and Ctenopty- 
chius, and some others. Labyrinthodont remains are also 
common. By far the most predominant fish is Coelacanthus; 
compared with all the others it is, individually, the most 
numerous. 
The special object to which I wish to draw attention 
is a very peculiar form of "ichthyodorulite," connected with 
what appears to be a portion of the exoskeletal plates of a 
* Read at British Association, Sheffield, 1879. 
+ See Prof. Green's Geology of the Yorkshire Coal Field, pp. ;>22-4. 
