CLASSIFICATION OF DEVONIAN FISHES. 



15 



former differ from the latter in the smoothness of their scales ; in 

 the structure of the roof of the cranium, whose constituent bones are 

 anchylosed into a singular shield, presenting some resemblance to 

 the cephalic shield of Acci2JeQiser ; and lastly, and chiefly, in the 

 peculiar form of the lower jaw, which much resembles that of a 

 Ccelacanth, and in their dentition, so well made known by Hugh 

 Miller, whose researches have been fully confirmed by Professor 

 Pander. 



In the next place, the true Ccelacanthini have a no less well-de- 

 fined right to occupy a similar position.* I say the true Ccelacan- 

 thini, because the term " Ccelacanth " has been used by different 

 palaeontologists with such very different meanings, has been made 

 in some cases to include so much, and in others to include so little, 

 that I feel it to be necessary to define precisely the sense in which 

 I employ it here. I intend it, then, to designate that family of 

 fishes of which the genus Goslacanthus of Agassiz is the type, a 

 family which, thus restricted, is as well defined and natural a 

 group as any in the animal kingdom, but, at present, can embrace 

 only the genera Coelacanthus, Undina, and Macropoma. 



In order to make this clear, however, I must enter at some 

 length into a historical and anatomical criticism of the Coelacanths 

 as a family of fishes. 



In establishing this family (" Recherches," vol. ii. p. 108), Professor 

 Agassiz dwells particularly upon the hollow fin rays of the typical 

 genus ; the absence of joints in some part of the length of most of 

 those fin rays ; the presence of interspinous bones in the caudal fin ; 

 the continuation of the vertebral column between the two lobes of 

 that fin, and the prolongation of the caudal extremity beyond it 

 as a filamentary appendage. With Gmlacanthus, Undina, Macro- 

 poma, Hoplopygus, Uronemus, Holoptychius, Glyptosteus, Glypto- 

 lepis, Psammolepis, Phyllolepis, Gtenolepis, and Gyrosteus are 

 associated ; and it is a curious circumstance that while Holoptychius 

 takes its place among the Coelacanths, without any special demon- 

 stration of its right to that position, Professor Agassiz hesitates 

 touching Macropoma, and, while admitting it into the family on 



* Several years ago Sir Philip Egerton strongly drew my attention to the close 

 affinity between the Ccelacanthini (jnihi) and what I have termed the Glyptodipterini, 

 particularly showing the importance of the lobate paired fins and of the double dorsals 

 common to the genera of both families (which Sir Philip Egerton was inclined to group 

 under the one head o^ ^Coelacanths'), and illustrating his views by a synopsis of the 

 genera. From the study of that synopsis I trace the gradual clearing up of my own ideas 

 respecting the difficult subject with which this preliminary essay attempts to deal. 



[X.] 10 B 



