162 WELLBURN : FISH FAUNA OF YORKSHIRE COAL MEASURES. 
and the following species of Pleur acanthus, viz., erectus Davis ; 
planus Agassiz ; Wardi Davis ; pulchellus Davis ; appear to have 
been founded on spines of Pleuracanthus in various stages of 
erosion. 
The following appear to be good species : — 
P. Icevissimus Agassiz, 1837. 
P. rohustus Davis, 1880. 
P. cylindricus Agassiz, 1843. 
P. alatus Davis, 1880. 
P. alternidentatus Davis, 1880. 
P. tenuis Davis, 1880. 
P. denticulatus Davis, 1880. 
P. horidus Traquair, 1881.* 
P. Wardi Davis ?, 1880. 
Form, and Loc. : See Table of Distribution. 
Genus: Diplodiis Agassiz, 1843. 
It certainly appears to the author that this genus should be 
merged with that of Pleui-acanthus. Teeth of Diplodus gihbosus 
Agassiz are found in the Staffordshire Coal Measures in such 
a close relation to P. cylindricus as to leave little doubt that they 
belong to one and the same fish ; again, in the Yorkshire Measures, 
where P. cylindricus Ag. is somewhat rare, teeth of the type 
D. gihbosus Ag. are less commonly met with than those of the 
type D. tenuis A. Smith Woodward. These facts appear to 
point strongly to the conclusion that the teeth D. gihbosus pertain 
to P. cylindricus, and those of the t3^pe D. tenuis to P. loivissimus 
and others. 
Sp. D. gihbosus Agassiz, 1843. 
Not very widely distributed or common. 
Sp. D. tenuis A. S. Woodward, 1889. 
Widely distributed and common. 
Family : Cladodontidte. 
Genus: Cladodus Agassiz, 1843. 
* There is a spine in the Natural History Museum, Cromwell Road, labelled 
P. horidus Traq. (from the Better Bed Coal), Clifton, near Halifax. 
