CLASSIFICATION OF DEVONIAN FOSSILS. 



27 



stiff- walled lungs of Lepidosiren, a structure more nearly repre- 

 senting the ossified air bladder of the Coelacanths than any with 

 which we are at present acquainted, among recent or fossil fishes. 

 Furthermore, Lepidosiren is the only fish whose teeth are compa- 

 rable in form and arrangement to those of DipterusJ^ Though 

 Lepidosiren may not be included among the Crossopterygidse, nor 

 even in the order of the Ganoidei, the relations just pointed out are 

 not the less distinct ; and, perhaps, they gain in interest when we 

 reflect, that while Polypterus, the modern representative of the 

 rhombiferous Crossopterygidse, is that fish which has the most 

 completely lung-like of all air bladders, Lepidosiren, which has 

 been just shown to be, if not the modern representative of the 

 cycliferous Crossopterygidse, yet their ''next of kin," is the only 

 fish which is provided with true lungs. These are unquestionable 

 facts. I leave their bearing upon the great problems of zoological 

 theory to be developed by every one for himself. 



The preceding discussion of the afiinities of the Devonian genera, 

 Osteolepis, Diplopterus, Glyptolwmus, Glyp>topomus, Gyropty chins, 

 Holoptychius, Glyptolepis, Dendrodus, Phaneropleuron, Dipterus, 

 was an indispensable preliminary to the consideration of the main 

 question with which I proposed to deal in the present essay, viz., 

 What, and how many, groups of fishes are represented in the Fauna 

 of the Devonian epoch? a Fauna which presents a surpassing interest, 

 when we recollect that it comprises the oldest assemblage of ver- 

 tebrate animals, of which we possess a more than fragmentary 

 knowledge ; that its constituents abound in certain localities ; and 

 that, for many years past^ they have been the subject of careful and 

 repeated collection and investigation. An examination of the data 

 collected up to the present time has led me to the following con- 

 clusions, some of which are already current, while others are new :— - 



1. No vertebrate animal higher in the scale than fishes is as yet 

 certainly known to have been found in any rock of Devonian age. 

 In fact, until demonstrative stratigraphical evidence of the Devonian 

 age of the well-known Elgin beds is obtained, the bearing of the 

 palseontological evidence against that conclusion is too strong to 

 allow of its being entertained. 



2. Of the six orders of the class Pisces, three, namely, the Dipnoi, 

 Marsipobranchii, and Pharyngobranchii, are certainly not repre- 

 sented by any known Devonian fish. In endeavouring to estimate 

 the value of this negative fact, we nmst recollect that no fish 



* Prof. Pander has drawn attention to the resemblance of the teeth of his genus 

 Holodus to those of Lepidosiren, Tbut it is not clear that he regards Holodus as a Cteno- 

 dodipterine. 



