﻿XV111 INTRODUCTION. 



occurring further backwards, and especially distinct in Cyathaspis l , 

 are exactly such as might result from contact with ridges upon the 

 auditor}' capsules, due to a great development of the upper semi- 

 circular canals, as in Sharks. In short, all positive characters 

 are rather in favour of an alliance with the class Pisces than 

 otherwise ; and although these organisms cannot be defined with 

 scientific precision, it seems advisable at present to regard them 

 as a primitive Piscine subclass of uncertain affinities. 



The name Ostracodermi is preferred for this subclass, because 

 Prof. Cope seems to be the only naturalist who has hitherto ven- 

 tured to remove the Coccostean fishes far from the order that com- 

 prises the Asterolepidae. So long ago as 1848, M'Coy 2 proposed to 

 institute the " family Placodermi " for the Asterolepidae and Cocco- 

 steidae, allowing Ceplialaspis to remain as the type of a distinct 

 family ; and all subsequent authors seem to have adopted this 

 arrangement, with only slight changes in the rank allowed to the 

 great divisions. Even so recently as 1888, Traquair 3 regarded the 

 Asterolepidae and Coccosteidae as separated by characters merely of 

 family value; and in the latest work of Newberry 4 , the same 

 classification, though not systematically formulated, is implied. It 

 must, however, be remarked that both Newberry, Traquair, and 

 other authors have on several occasions pointed out the close 

 resemblance between the dentition of the Coccosteidae and that of 

 the Dipnoi ; and it is by extending this suggestion to its logical 

 issue, in the light of the latest researches, that the classification 

 adopted in the following Catalogue has been attained. The Cocco- 

 steidae and their allies possess ossified jaws and a dentition that are 

 far from incipient or rudimentary. Some are believed to have had 

 pectoral fin-spines (e. g., Dinichihys and Brachydirus) — a circum- 

 stance implying the presence of highly specialized paired fins ; and 

 even where pectorals have not been observed (e. g., Coccosteus), 

 membrane-bones identical with those of an ordinary pectoral arch 

 are certainly well developed. Coccosteus, moreover, is now proved 

 to exhibit highly specialized pelvic fins. These characters suffice, 

 at least in the present state of knowledge, to separate the Coccosteus- 

 like fishes very widely from those now termed Ostracodermi ; and 

 it may be added that even detached fragmentary plates can in many 



1 See Kunth, von Alth, and Lankester's figures already quoted. 



2 F. M'Coy, Ann. Mag. Nat. Hist. [2] vol. ii. (1848), p. 6. 



3 K. F. Traquair, Geol. Mag. [3] vol. v. (1888), pp. 508, 511. 



4 J, S. Newberry, ' Palaeozoic Fishes N. America' (1889). 



