FISHES OF THE CARBONIFEROUS SYSTEM. 213 
The several species which have been enumerated differ from each other 
in size, the relative height and length of scales, or the ornamentation of the 
head bones. Probably some of these differences are dependent upon sex, 
age, or accidental variation within specific limits, but the great diversity in 
the altitude of the side scales—from double to five times the length—and 
the linear or tuberculated ornamentation of the cranium seem to prove that 
there were at least half a dozen distinct species. Although so numerous in 
this locality that many hundred individuals have been collected, no repre- 
sentative of the genus has been found elsewhere except a single specimen 
which I detected in the collection of Mr. J. C. Carr, of Morris, Il. 
The next most abundant fish at Linton is Celacanthus elegans ; yet while 
perhaps a thousand specimens more or less perfect have been taken from 
one coal mine there, with the exception of a single one found at Morris no 
representative of this world-wide genus has been elsewhere seen in America. 
The Elonichthys (E. peltigerus, N.) which appears in the list recurs in 
the cannel coal at Canfield, Ohio, and at Morris, Il. 
Perhaps the most interesting element in the Linton fauna is Calacanthus 
elegans, N. This is so much like C. leptwrus of the English Coal Measures, 
that I have been doubtful whether it should be regarded as distinct; the 
only observed difference being the greater continuity and parallelism of the 
thread-lines which ornament the scales, jaws, and jugular plates of the Lin- 
ton fishes. They are at least so much alike as to show that they have 
been derived from a common ancestry, and that the inhabitants of the 
widely separated localities where they are found came by migration from a 
common place of origin. 
The similarity, not to say identity, of structure in this highly specialized 
group of fishes is a striking illustration of the tenacity with which organic 
forms hold to their characters through long periods of time and in diversified 
surroundings. The migration of these fishes must have been through bodies 
of fresh water, necessarily very slow and through great changes of environ- 
ment, yet their very complicated structure, in both essentials and ornamen- 
tation, has been entirely unaffected by time—which would favor spontane- 
ous or inherent variation—and circumstance, usually supposed to have 
almost unlimited modifying power. 
