X 
INTRODUCTION. 
scribed by Agassiz; and all other known Elasmobranchs were 
grouped in a second order, which might be conveniently named 
Selachii. 
Palaeontological Resources. 
Several other descriptions of fossil Elasmobranch skeletons already 
published, in addition to those contained in the present volume, 
permit of a still more satisfactory discussion of the subclass from a 
Palaeontological point of view; but before summarizing the main 
facts at present available, it may be of some interest briefly to note 
the sources whence most of the information has been gleaned. 
The detached teeth of Sharks discovered in the Tertiary deposits 
have been known for a long period • and in the seventeenth and 
eighteenth centuries these formed the subject of several learned 
treatises. The fossils became known as Glossopetrce, and it was not 
until Steno 1 and Scilla 2 3 compared them with the teeth of recent 
sharks, giving excellent figures and descriptions, that their true 
nature could be regarded as definitely established. This happened 
in the eighteenth century; but it was only so recently as the re¬ 
searches of Buckland and I)e la Beche, about 1830, that the fossil 
dorsal fin-spines of Elasmobranch fishes were identified. These 
remarkable petrifactions long perplexed the earlier naturalists, one 
(Asteracanthus) being described and figured in 1753 3 as “ the head 
or snout of some animal of the fish kind, or perhaps of some lizard, 
alligator, or crocodile,” and another (Gyracanthus) was long supposed 
to be the seed-pod of some extinct plant 4 . Buckland and De la Beche 
termed the fossil spines “ Ichthyodorulites ” ; Agassiz named many 
of them, and assigned a few to their correct zoological position : and 
even yet several types remain to be definitely determined. 
The great work of Agassiz was the first to place the study of 
Elasmobranch Paleontology upon a truly scientific basis : and the 
third volume of the 4 Iieoherches sur les Poissons Eossiles ’ (1837 - 
43) still forms the groundwork of the whole subject. Here, for the 
first time, are not only described, in as precise a manner as possible, 
the numerous detached teeth and spines ; but the Lower Lias of 
Lyme Regis, the Lithographic Stone of Bavaria, and the Tapper 
Cretaceous of Westphalia, furnish more or less well-preserved re- 
1 De Solido intra Solidum naturaliter contento, 1669. 
2 De Corporibus marinis lapidescentibus, 1752. 
3 H. Baker, Phil. Trans. 1753, p. 118, pi. vi. 
4 See J. D. 0. Sowerby, Zool. Journ. vol. i. (1825), p. 252, pi. viii. fig. 9. 
