276 Evolution and Distribution of Fishes 



future pages, we may next refer to Professor John Young's 

 "Catalogue of the Western Scottish Fossils" (///). On 

 p. 60 he says, "the remains of fishes extend from the lower 

 beds of the Calciferous series, up through the several 

 divisions of the Limestone strata, Middle Coal and Iron- 

 stone, Millstone Grit, and Upper Coal Measures. Two 

 groups are represented viz. lepidoganoids and plagiostom- 

 ous fishes. The former are chiefly confined to the fresh- 

 water or brakish water strata^ being very rarely met with 

 in any of the beds of purely marine origin. The remains 

 of plagiostomous fishes, on the other hand, are found in 

 both maj'ine and freshwater strata, certain genera being 

 peculiar to each of these groups." 



He then gives an extensive list that includes upwards 

 of sixty elasmobranchs, but of these nearly half are from 

 marine limestone rocks. All of the others are from coal, 

 from shale associated with coal, or from blackband iron- 

 stone, which, by its fossils the present writer has proved to 

 be usually associated with plant remains, eurypterids, etc., 

 while marine organisms are absent. Young fortunately 

 quotes extensively ecological associations of animals, in the 

 latter part of his paper, from which we may extract the 

 following: 



( 1 ) From the roof shale of the Palace Craig iron- 

 stone he gives the amphibians Pholadej'peton sp. Pteroplax 

 corniita, Anthracosaurus russelli and Loxomma allmanni, 

 the freshwater crustacean Anthrapalaemon grossartii, the 

 mollusc Jnthracosia, several species of Lepidostrobus 

 cones, the elasmobranch fishes Acanthodes wardi, Gyracan- 

 thus formosus, G. tuberculatus, Ctenacanthus major, Diplo- 

 dus gibbosus, and Cladodus; the dipnoans Ctenodus 

 cristatiis and C. tuberculatus; the crossopterygians Strepso- 

 dus sauroides, Megalichthys hibberti, M. coccolepis and M. 

 rugosus. Here, therefore, a goodly list of fishes is directly 

 associated with amphibians that cannot tolerate saltwater, 

 as well as with many other freshwater types. 



(2) In Broadstone beds S. E. of Beith he describes a 

 'lot of typically marine organisms, but gives with them the 

 elasmobranchs Psammodus rugosus, Ctenoptychius serratus, 



