INTRODUCTION. 
There is no more striking instance of the difficulty of interpreting 
fossil remains by a close comparison with the skeletons of existing 
animals, than that presented by the Palaeozoic Pishes. 'When 
the first fragments of Coccostean plates from the Lower Old Eed 
Sandstone of Caithness were noticed by Sedgwick and Murchi¬ 
son sixty years ago, nothing more closely similar among existing 
animals could be found than the dermal plates of the mud-tortoises. 
Trionyx was accordingly entered in the list of Caithness fossils h 
Nearly eight years later, the Russian geologist Kutorga 1 2 , when 
attempting to interpret fragmentary teeth and dermal plates from 
the corresponding formations of Livonia, was led to name a long 
series of mud-tortoises, lizards, and Ichthyosauri from that country, 
giving good figures and detailed descriptions of the evidence upon 
which the restoration of so remarkable and unexpected a fauna was 
based. Even when such entirely erroneous impressions were re¬ 
moved by the discovery of more satisfactory specimens, and when 
the far-reaching researches of the ichthyologist, Louis Agassiz, had 
shown that all these remains pertained to fish-like organisms no 
longer existing, the same tendenc}- to interpret the past by a rigorous 
comparison with the present everywhere prevailed, and the frequent 
result was a distortion of the facts of structure in the fossils to con¬ 
form to arrangements observed in the present fish-fauna. Not only 
was Hugh Miller induced, by Agassiz’s researches, to compare in 
detail the skulls of some of the Old Eed genera with that of the 
living cod-fish 3 , but this recent gadoid was actually used by Agassiz 
1 Trans. Geol. Soc. [2] vol. iii. (1829), p. 144, pi. xvi. fig. 6. 
2 S. Kutorga, ‘ Zweiter Beitrag zur Geognosie und Palaontologie Dorpai’s/ 
1837. 
3 H. Miller, ‘ Footprints of the Creator,' (1849), p. 48. 
