AND MESOZOIC FISHES. 
4.0 
It is further to be observed that the essential distinction now discovered be- 
tween the nietapterygial and other elements of the paired fins, must be maintained 
in our future studies of them. A clear distinction between baseosts and axonosts 
in the paired fins has been hitherto wanting. For the present it may be convenient 
to regard the nietapterygial elements as axonosts, and those which have originally 
been brandies of that axis, as baseosts. The scapular base of the Selachian fin 
(Fig. 2) consists then of one axonost and two baseosts. The Actinopterygian fin 
will have as its scapular base, according to (legenbaur’s homologies, baseosts only, 
the nietapterygial (axonost) elements having entirely disappeared (Fig. 8). 
Taxonomy . — As a result of the preceding observations, I have removed the 
Cladodontidae’ from the Ichthyotonii, where Dr. Woodward placed them, and have 
relegated them to his order of Acanthodii. The definitions of the three orders de- 
rived from the fins, will then be as follows ; those of the second and third Inung the 
same as given by me in the American Naturalist f()r 1889 (October, p. 8b4): 
Paired fins ptychopterygial ; Acanthodii. 
Paired fins archipterygial ; Icliylhotomi . 
Paired fins basilo-metapterygial ; Sclachh. 
Char. Specif . — This species is established on the anterior jiart of the skeleton 
of an individual from the shales of the Coal Measures near (lalesburg. Knox (A)., 
Illinois. The fragments include parts of the skull, hyoid arches and pectoral andi, 
in a damaged condition. The jaws, which are preserved, display a considerabh' num- 
ber of teeth more or less displaced. One mandibular ramus is i<lenti(iable, but the 
other tooth-bearing elements are not certainly determinable. 
The teeth display all their surfaces, so that their characters an* readil\' a.scer- 
tainable. They are all alike, differing only in size, those near the center of the 
specimen being smaller than those more distant, and representing probably a more 
posterior position on the jaws. The base of the tooth is renifonn in outline, the 
anterior border concave, the posterior convex, and the extremities obtnsidy rounded, 
or subtruncate. The principal cusp is about as high as the base is long. It is flat- 
tened anteriorly, and very convex posteriorly, and is curved backward. The 
anterior surface is finely^ striate, and the posterior face is more strongly and sharply' 
striate with clo.se and fine ridges. The two faces are sepanited by a cutting i-dge. 
The apex is smooth, and pjresents a low angle on the anterior lace. There are two 
ba.sal cusps on each .side, the external larger, but much smaller than the median. It 
is curved backward, has no cutting edges, and the .surface is striate-groovcil. I he 
middle cusps are smaller, and acutely conic. All the cusps stand on the anterior 
border of the base. 
The characters above enumerated show that this species diflers from ea<di of 
the numerous forms de, scribed by Newberry in the reportsol the ( icological Surveys 
of Ohio (Vol. II). and Illinois (Vol. 11), or by St. John in the same (\ol. \ I). or by- 
Newberry in his work on Paleozoic Fishes in the Monograph No. X \ 1 of the I . S. 
Geological Survey. It resembles most C. lanmotdes Newb. and C. intercostaius, 
' Anier. Naturalist, 1898, Nov., p. 999. 
