532 FOSSIL FISH OF THE [Ch. XXVI. 



genera were afterwards published by Sir P. Egerton, whose labors in 

 this field (including a synopsis of all the genera known in 1857) have 

 been acknowledged by Professor Huxley as haying powerfully con- 

 tributed to clear up his ideas when he undertook, in 1861, the difficult 

 task of classifying these fishes. To the Russian zoologist, Pander, we 

 are also indebted for a most able treatise on these ichthyolites. Pro- 

 fessor Huxley's masterly essay is of a later date "than Pander's, and 

 contains a systematic arrangement of the British Devonian fish, which, 

 he observes, are of surpassing interest, as comprising the oldest assem- 

 blage of vertebrate animals of which we can be said to have any toler- 

 ably complete knowledge ; for no reptiles have yet been found older 

 than those of the coal, and the Silurian fish are confined to a few 

 isolated specimens, affording us a very scanty insight into the character 

 of the piscine fauna anterior to the period of the Old Red Sandstone. 



The Devonian fish were referred by Agassiz to two of his great 

 orders, namely, the Placoids and Ganoids. Of the first of these, which 

 in the Recent period comprise the shark, the dog-fish, and the ray, no 

 entire skeletons are preserved, but fin-spines called Ichthyodorulites, 

 and teeth occur. On such remains the genera Onchus, Odontacanthus 

 and Ctenodus, a supposed cestraciont, and some others, have been 

 established. There are also some spiny fish of a family called Acan- 

 thodidse, not yet well understood, and thought by Huxley to have 

 some connection with the Placoids, although he admits that they may 

 perhaps have still more claims to rank with the Ganoids, with which 

 they have been usually classed. 



Among the Ganoids are the Cephalaspidas (see fig. 589, p. 526), rep- 

 resented by several genera, Cephalaspis, Pterasjns, &c, and forming a 

 very distinct family, but having, according to Huxley, a considerable 

 relationship with the sturgeon. 



By far the greater number, however, of the Old Red Sandstone fishes 

 belong to a sub-order of Ganoids instituted by Huxley in 1861, and for 

 which he has proposed the name of Crossopterygidce* or the fringe- 

 finned, in consideration of the peculiar manner in which the fin-rays 

 of the paired fins are arranged so as to form a fringe round a central 

 lobe, as in the Polypterus (see a, fig. 598), a genus of which there are 



Polypterus. See Agassiz, " Eecherches sur les Poissons Fossiles." 

 Living in the JSTile and other African rivers. 

 a. One of the fringed pectoral fins. c. Anal fin. 



h. One of the ventral fins. d. Dorsal fin, or row of finleis. 



* Abridged from upooacdTOQ, crossotos, a fringe, and rrrepv^ pteryx, a fin. 



