PHYLUM VIII VERTEBRATA 1 1 1 



Devonian of the Eifel, Nassau, Westphalia, and Belgium. Gigantic Arthrodires 

 (Dinichthys, 2'itanichthys, Diplognathus) and Selachii are remarkably abundant 

 in the Middle and Upper Devonian ,of Ohio, Wisconsin, and New York. 

 The Devonian fish fauna consists of Arthrodires, Ostracoderms, many Ganoids 

 (Crossopterygii and Heterocerci), Dipnoans (Ctenodipterini), and Selachians 

 (Pleuropterygii, Acanthodii, Holocephali). 



The fishes of the Carboniferous System are obtained partly from the 

 marine Carboniferous Limestone, partly from the shales and sandstones of the 

 productive Goal Measures. The enormous development of the Selachii,^ of 

 which, however, only teeth and fin spines are commonly preserved, sharply 

 distinguishes the Garboniferous fish fauna from that of the Devonian period. 

 The Gochliodontidae, Psammodontidae, and Petalodontidae are almost ex- 

 clusively confined to the Garboniferous Limestone, while the Gestraciontidae 

 are also well represented ; the Acanthodians and Pleuropterygians continue, 

 the Pleuracanthidae begin. The heterocercal Ganoids are the principal 

 associates of the Selachii ; the Grossopterygii and Gtenodipterini are still 

 present, but in diminished numbers. 



The fishes of the Permian system are closely similar to those of the pro- 

 ductive Goal Measures. They occur in the Rothliegenden of the Saar Basin, 

 Bohemia, Saxony, Silesia, and France ; in the Magnesian Limestone of England; 

 in the Kupferschiefer of Thuringia and Hesse ; and in the probably contempor- 

 aneous strata of Texas and New Mexico. The Heterocerci are by far the most 

 numerous. Of the Grossopterygii, Coelacanthus and Megalichthys alone survive in 

 Europe. Among the Dipnoi, the genera Ctenodus and Sagenodus are especially 

 widely distributed. In comparison with the Garboni'ferous fish fauna, that of 

 the Permian period is noticeably destitute of Selachii. Here, however, the 

 remarkable Pleuracanthidae attain their maximum development, and are 

 associated with a few Gochliodontidae {Menaspis), Petalodontidae (Janassa), 

 and Acanthodidae. 



The abrupt break in development, which is observable in most sections of 

 the animal and plant world at the close of the Palaeozoic epoch, is also 

 conspicuous among the fishes, although the Ti'iassic fish fauna exhibits many 

 resemblances to that of the Permian. Among Selachii, the Pleuracanthidae, 

 Gochliodontidae, and Petalodontidae are wanting ; the Plagiostomi, on the 

 other band, are well represented. Teeth and fin spines of the Gestraciontidae, 

 for example, are very numerous in the Muschelkalk and uppermost Keuper. 

 The occurrence of heterocercal scaly Ganoids of the family Palaeoniscidae, as 

 well as the persistence of a few Grossopterygians, is indeed reminiscent of 

 Palaeozoic times ; but the most numerous and best preserved Triassic fishes 

 belong to the enamel-scaled Lepidostei, of which the Permian system aff'ords 

 only a single genus (Acentrophorus). Among the Dipnoi the persistent 

 Ceratodus, represented principally by teeth, plays an important part. The 

 Teleostei are already represented by some small Glupeoids {Megalopterus). 



The fish fauna of the Lias is a direct continuation and further development 

 of that of the Trias. No less than 152 species were described by Agassiz and 

 Egerton, and of these 79 occur only in the Lower Lias of Lyme Regis in 

 Dorset. The Middle Lias contains few fishes ; but the Posidonia shales and 

 bituminous limestone of the Upper Lias e in Swabia and Franconia, as well as 



1 Hay, O. F., The Chiouological Distribution of the Elasniobraiichs (Trans. Amer. Phil. Soc. 

 vol. XX.), 1901. 



