42 PALEOZOIC FISHES OF NORTH AMERICA. 
lines, forming a pattern which does not correspond with the plates below; eye orbits 
conspicuous, inclosed in the orbital (frontal ?) plates; nasal plate (ethmoid ?) wedge- 
shaped, the apex turned backward, and reaching to the center of the cranium; occip- 
ital plate (supra-occipital) oblong, emarginate behind, prolonged anteriorly iuto a 
point, which meets the opposing point of the nasal plate; teeth and scales unknown, 
probably wanting. 
Since the publication of the above description numerous heads of Ma- 
cropetalichthys have been found at different places in the Corniferous lime- 
stone, and two of these which I have examined show the under surface. 
This is in a general way flat and smooth, but is marked by a transverse 
furrow, which probably indicates the position of the mouth. No jaws or 
teeth are visible, and it is almost certain that fishes of this genus had no 
bony jaws or teeth; otherwise they would long since have been discovered. 
It seems probable, therefore, that the mouth of Macropetalichthys was like 
that of the sturgeons, with which I am inclined to associate it, soft and suc- 
torial. Whether there were rudimentary jaws like those of Acipenser 
attached to the head of Macropetalichthys we cannot say, but it is quite pos- 
sible. Yet, even if jaws were wanting, that would seem to me no good 
reason why this should not be considered a fish and a member of the order 
Chondrosteide. 
Professor Heeckel has made the possession of an under jaw a condition 
of the acceptance of any organism as a member of the class of fishes; but 
this seems to me to be unphilosophical and unwarranted. No one can say 
to what limits the atrophy, by modification or disuse, of any single organ 
among the vertebrates may be carried. Perhaps nine-tenths of the organs 
might remain distinguishable and even normal while one perished, and it 
is a short-sighted philosophy which would classify the animal kingdom by 
arule so narrow. A wing is generally regarded as a characteristic and es- 
sential organ in a bird, but we know that in Apteryx and Dinornis the wings 
are practically obsolete, and yet no one would dare to exclude these from the 
class of birds. Macropetalichthys was evidently a large and doubtless nor- 
mal member of the great group of fishes which led and gave character to 
the life of the Devonianage. As I have elsewhere urged, it was undoubtedly 
a fish, and probably an ancestral form of the sturgeons of to-day. Indeed, 
it has been a matter of surprise to me to find that it represented so well the 
