﻿STRUCTURE OF THE PALjEONISCIDjE. 



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The Palaoniscidce are thus seen, as far as our present information goes, to have first 

 appeared in the Old Red Sandstone formation, and finally to have died out in the earlier 

 part of the great Jurassic era. Their remains are, however, most abundant in and 

 characteristic of rocks of Carboniferous and Permian age. 



STRUCTURE AND SYSTEMATIC POSITION OF THE PALiEONISCIDvE. 



Hitherto there has been very little done in the way of accurate research into the 

 anatomical structure of the Palaoniscida, especially as regards their cranial osteology, and 

 consequently the opinions of naturalists as to their relationships with other groups of 

 fishes, living and extinct, have not rested on a very secure basis. This is in a great 

 measure due to the condition in which their remains usually occur ; the delicate 

 internal skeleton of the trunk being usually more or less completely obscured by the 

 external scaly covering, while the bones of the head are in most cases so crushed, 

 broken, and squeezed together as to render their interpretation a very difficult matter 

 indeed. 



The information derivable on these points from the writings of Agassiz is not very 

 extensive, or of a very definite character ; in fact, the Palaoniscida as a group were not 

 understood by the illustrious author of the ' Poissons Fossiles.' For, notwithstanding 

 certain obvious structural correspondences between the various Palseoniscoid genera with 

 which he was acquainted, they were classed by him in three separate families, and in 

 each case associated with the most dissimilar neighbours. While Palceoniscus, Ambly- 

 pterus, Gyrolepis, and Centrolepis were included in the family of " Lepidoides," Pygopterus, 

 Acrolepis, and Tkrissonotus found a place among the " Sauroides," and Cheirolepis among 

 the " Acanthodiens " — the mere size and arrangement of the teeth being relied on as the 

 great mark of distinction, and, in the aberrant genus Cheirolepis, the minuteness of the 

 scales. And although from some of the descriptions in the text it is evident that he was 

 acquainted with many of the bones of the head, yet his restored figures, some of which, 

 like that of Palaoniscus (Atlas, vol. I, tab. A, fig 4), have been so often copied into 

 other works, are very erroneous, and completely ignore the peculiarities of the family. 



Quenstedt in his ' Handbuch der Petrefactenkunde ' (Tubingen, 1852, pi. xviii, figs. 

 3, 4, 5, 6) gives a few figures illustrating the bones of the head of Palaoniscus and 

 Pygopterus, which, so far as they go, are very accurate. We may note here especially 

 his recognition of the true form of the maxilla, of the peculiar backward slope of the 

 operculum, and the enormously wide gape characteristic of the family. The figure of 

 Amblypterus latus (fig. 5) is not, however, so great a success. 



In 1869 I published a description of the fish from the Wardie Shales named by 



