CARBONIFEROUS FISH-FAUNA 
the fish-fauna are proved to be without real foundation. Tar 
from displaying a “ Mixture of Lower Devonian, Upper Devon- 
ian, and types related to some of the Calciferous Sandstone 
series,” as McCoy supposed, the Mansfield fishes are typically 
and essentially Carboniferous, as the following technical descrip- 
tions will demonstrate. Of the six genera represented in the 
collection, one ( Eupleurogmus) is too imperfectly known for 
discussion ; four of the others ( Acanthodes , Ctenodus, Strepsodus, 
and Elonichthys) have hitherto been discovered only in the 
Permian and Carboniferous of Europe, and in the Carboniferous 
of North America; while the sixth (Gy vacant hides) is related to 
an essentially carboniferous fish in the northern hemisphere and 
bears every mark of belonging to the same late Palaeozoic period. 
The genus Gyracanthides is, indeed, a remarkable discovery. 
As correctly recognised by McCoy, it is closely allied to Gyracan- 
thus , which is widely distributed as a characteristic fossil in the 
Carboniferous of the northern hemisphere and seems to be also 
represented by a few small spines in the Lower Devonian. The 
new specimens prove that Gyracanthides is a typical Acantho- 
dian, belonging either to the Diplacanthidoe or to a distinct 
family which marks the culmination of the Diplacantli series. 
The enlargement of the pectoral fins, the reduction and forward 
displacement of the pelvic fins, and the absence or peculiar modi- 
fication of the intermediate spines, are features indicating its 
high degree of specialisation. It occupies the same position 
among Diplacanths as that occupied by the Permian species of 
Acanthodes among the Acantliodians with one dorsal fin . 1 It 
shows that the direction of specialisation was identical in the two 
great groups of Acantliodians, and was analogous to the speciali- 
sation observable in later geological periods among Selachians and 
Teleosteans. 
The total assemblage of fishes in the red rocks of Mansfield is 
such as occurs usually in estuarine or freshwater strata in the 
northern hemisphere ; but all the genera are likewise met with 
1. A. S. Woodward, “ Catalogue of Fossil Fishes in the British Museum,” pt. ii (1891) 
p. 5. 
