MITCHELL— ACANTHODES IN PALAEOZOIC EOCKS. 



131 



Scotland, in the summer of the year 1857. From investigations 

 since made, it now appears that an abundant flush of Acanthodian 

 life ushered in the morning of the vast period embraced by the Old 

 Eed Sandstone. Along with the genus Acanthodes there occur also 

 several other genera of the Acanthodian family, such as Climatius, 

 Parescus, and some unnamed. The genera Climatius and Parescus 

 were first founded upon and described by Agassiz, in his great work, 

 from spines, but since the perfect forms have turned up in our 

 northern rocks, it has been found necessary to remove them from 

 among the Cestraciont Placoids into the Acanthodian family of the 

 Ganoids, that is to say, provided we adhere to the classification of 

 Agassiz. Other genera and species occurring with us remain to be 

 described, and we are very much disposed to think that the spines 

 figured from the Ludlow bone-bed in the Upper Silurian must be 

 relegated to Acanthodian forms. Much as has been made of it, have 

 we any evidence of the occurrence of Placoidal fishes in those rocks 

 at all, except pieces of shagreen-looking skin ? What if these, on 

 closer scrutiny, turn out to be Crustacean and not Piscine remains ? 

 Would it not be worth the while of some of the earnest observers in 

 that region to examine carefully those Ludlow beds, or especially 

 their equivalents, where spines occur, for the complete forms ? It 

 was long thought that in our Scottish rocks of the Lower Devonian 

 we had nothing but unattached spines of these fossil fishes. 



It may be observed, in order to remove all doubt of the position 

 here assigned to the beds of the Old Red Sandstone in which Acan- 

 thodes first occurs, that we have specimens on the same slabs with 

 plates of the Pterygotus, and in the same stone with Cephalaspis 

 Lyellii. It may be that other species of Acanthodes occur in our 

 Lower, but it is certain that in the Middle beds of the Old Eed, as 

 they occur in Moray and Caithness, there is a fuller development of 

 species. But in such a feature the genus would resemble many others 



! in the geological muster-roll of being, — presenting us first with a 

 weak dawn, — then culminating into meridian fulness, but again sink- 

 ing into a slow decline and final extinction, yet still preserving 

 throughout the career of their existence the characteristic traits of 

 their generic life, the dying representative of the genus is not how- 



! ever a degraded form, but is as beautiful and as highly a developed 

 creature as its first introduced ally. The outline of the body of the 

 Acanthodes of the Lower Devonian Egerton describes as remarkably 

 graceful, and Kdmer has given the specific appellation of gracilis to 

 the Acanthodes of the Lower Permian, 



It is certainly worthy of remark that the genus Acanthodes is per- 

 sistent through such a lengthened period of geological existence ; and 

 from such a circumstance we are inclined to infer that as the details 

 of the stony record are filled up, all gaps will disappear. We do not 

 and cannot admit the truth of the theory of the transmutation of 

 species, yet the course of creation has not proceeded by sudden 

 bounds, but by a steady, calm advance. There is no evidence, so far 



