GANOID FISHES. 425 



Selachians, Ganoids, and Batrachians. Chimcera plumbea 

 Gill lives in deep water off the coast of New England. 



Subclass 2. G-anoidei (Gar pikes, Lung - Fishes). The 

 term Ganoid was applied to these fishes from the form of 

 the scales, which in most of the species are angular, square, 

 or rhomboidal and covered with enamel, as seen in the com- 

 mon garpike. In others, however, as in the Ami a and Dip- 

 noans, the scales are rounded or cycloid. These fish, i.e., 

 both the genuine Ganoids and Dipnoi, were the character- 

 istic fishes of the Devonian age, which has consequently been 

 called the Age of Fishes, there being no bony fishes (Teleos- 

 tei) at that time. The forms Avere much larger than at 

 present, far more numerous in species, genera, and families, 

 and they, with the sharks, were the rulers of the sea. 



At the present day the type is nearly extinct, being repre- 

 sented by such isolated forms as the sturgeon, the paddle- 

 fish, the lung-fish (Dipnoi), the garpikes, and the American 

 mud-fish (Amid). Like most of the palaeozoic types of life, 

 the Ganoids were both generalized forms and also combined 

 the characters of classes of animals not then in existence ; in 

 other words they were synthetic or comprehensive types. 

 Thus in forms like Amia, the Teleostean fishes were antici- 

 pated ; in the Dipnoi, with their external gills and lungs, 

 not only the Amphibians, but even the reptiles were indica- 

 ted in their hearts with two auricles, just as the Trilobites and 

 Merostomata, as indicated by the structure of the living 

 king-crab, combined with the structure of Crustaceans, fea- 

 tures which became in a degree reproduced in the terrestrial 

 scorpions and spiders which subsequently appeared. Owing 

 to this intermixture of ancient and modern characteristics, 

 this reaching up and out of the piscine type of life over into 

 the amphibian and reptilian boundaries, the classification, 

 i. e., actual position in nature of the Ganoids, becomes very 

 difficult, and the views of naturalists regarding their system- 

 atic position are very discordant. If, as insisted on by Gill, 

 we recognize the fact that the Ganoids are an older, more 

 generalized, and therefore more elementary group, and the 

 osseous fishes a newer, more highly specialized group, and 



