VI 
INTRODUCTION. 
himself to impart a life-like aspect to the head in his restored 
figure of the Dipnoan and Crossopterygian genera Dinierus and 
Diplopterus b In the interpretation of fins, again, close comparison 
with existing fishes led to some noteworthy fundamental errors, 
such as the restoration of the dorsal fin of Coccosteus 1 2 , as if it per¬ 
tained to the most modern specialized type ; and many other cases 
might he cited of an essentially similar character. Quite in modern 
times, indeed, the reiterated association of the Cephalaspidse, Astero- 
lepidae, and Coccosteidae with recent Sturgeons by Owen 3 ; the still 
more elaborate comparison of the Coccosteidae with existing 
Siluroids by Huxley 4 ; and the quite recent adhesion to this Silu- 
roid theory by Hewberry 5 6 —all must now be regarded as resulting 
from too narrow a conception of the limits within which certain 
minor skeletal characters may occur. The ascertained facts of 
embryology and the well-established broad principles of palaeonto¬ 
logy are now at the disposal of the investigator ; and it is hoped 
that a detailed review of the whole subject, s^ch as is attempted for 
the first time in the present volume, may tend towards a more 
philosophical understanding of the early representatives of the class 
under consideration. 
The first essential fact requiring special emphasis, at the outset, 
seems to be, that although the Paheozoic fishes certainly belong to 
the most generalized great divisions of their class, a large proportion 
of the known types are extremely specialized members of these 
divisions. This is clearly indicated by the characters of the fins in 
many forms. Just as in the existing fauna, the most striking 
examples of extreme specialization are comprised within the dominant 
higher groups of Actinopterygian Teleostomi, so in the Palaeozoic 
fauna the same instances of development occur almost exclusively 
in the then dominant orders of the Ostracodermi, Elasmobranchii, 
and Crossopterygian Teleostomi. If in the one case specialization 
proceeds sometimes almost exactly in the same manner as it does in 
the other, everything seems to point to the conclusion that this is 
1 L. Agassiz, ‘ Poissons Fossiles du Vieux Gres Fouge,’ (1844), pi. E. 
2 L. Agassiz, ibid. pi. vi. fig. 3. 
3 F. Owen, ‘ Pakeontology,’ ed. 2 (1861), p. 139 ; and ‘Anatomy of Verte¬ 
brates,’ vol. i. (1866), p. 12. 
4 T. H. Huxley, “ Preliminary Essay upon the Systematic Arrangement of 
the Fishes of the Devonian Epoch ” (Mem. Geol. Surv. dec. x. 1861), p. 29. 
6 J. S. Newberry, “ The Palaeozoic Fishes of North America ” (Mon. U. S. 
Geol. Surv. no. xvi. 1889), p, 141, et passim. 
