CHAPTER II 
THE GANOIDS—Continued 
LASSIFICATION of Ganoids. — The subdivision of the 
Nl series of Ganoidei into orders offers great difficulty 
from the fact of the varying relationships of the mem- 
bers of the group and the fact that the great majority of the 
species are known only from broken skeletons preserved in the 
rocks. It is apparently easy to separate those with cartilaginous 
skeletons from those with these bones more or less ossified. It 
is also easy to separate those with bony scales or plates from 
those having the scales cycloid. But the one type of skeleton 
grades into the other, and there is a bony basis even to the 
thinnest of scales found in this group. Among the multitude 
of names and divisions proposed we may recognize six orders, 
for which the names Lysoptert, Chondrostei, Selachostomt, 
Pycnodonti, Lepidostet, and Halecomorphi are not inappropriate. 
Each of these seems to represent a distinct offshoot from the 
first primitive group. 
Order Lysopteri.—In the most primitive order, called Lysop- 
teri (Avoods, loose; mrepor, fin) by Cope, Heterocerci by Zittel 
and Eastman, and the ‘‘ascending series of Chondrostei” by 
Woodward, we find the nearest approach to the Chondropter- 
ygians. In this order the arches of the vertebree are more or 
less ossified, the body is more or less short and deep, covered 
with bony dermal plates. The opercular apparatus is well 
developed, with numerous branchiostegals. Infraclavicles are 
present, and the fins provided with fulcra. Dorsal and anal 
fins are present, with rays more numerous than their supports; 
’ 
ventral fin with basal supports which are imperfectly ossified ; 
caudal fin mostly heterocercal, the scales mostly rhombic in 
form. All the members of this group are now extinct. 
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