INTEODUCTION. 
The present volume being the first attempt at a systematic treat- 
ment of the Palaeontology of the Elasmohranch fishes, it seems a 
fitting occasion for briefly reviewing the hearing of the newly- 
collected evidence upon the various results that have already been 
attained in the study of the existing members of this great sub- 
class. Notwithstanding its imperfections, Paleontology must neces- 
sarily be employed as the test — if it be »iot adopted as the basis — 
for all morphological and taxonomic speculations ; and though the 
pages of the Catalogue may indicate extreme imperfection in our 
knowledge of the past history of most groups, there are still a few 
well-ascertained facts which may be already profitably discussed 
with reference to the conclusions of recent Zoology. 
It is therefore proposed: — firstly, to enumerate the principal 
stages by which the most modem schemes of classification of the 
group have been elaborated ; secondly, to summarize the known 
and available palaeontological resources ; thirdly, to recapitulate the 
more important palaeontological results ; and lastly, to discuss these 
• results in the light of modern theories of taxonom}’. 
Taxonomic Deductions from the Study of Eecent Elasmobranchs. 
From the time of Aristotle and Pliny, fishes with a cartilaginous 
skeleton have been more or less clearly distinguished from those 
possessed of well-formed bones ; and when \\'illughby and Ray in- 
augurated the era of modern Ichthyologj' in 1686, they assigned to 
the “ Pisces Cabtilaoinei ” the lampreys, sharks, rays, and stur- 
geons *. In 1738, Artedi “ confirmed this arrangement, elaborating 
details, and applying the name of Chonlropterygii to an “ order ” 
comprising the existing types just mentioned; and Linnmus^ after- 
* J. EaiuB, F. Willughbeii de Historia Piscium (1086), p. 22. 
’ P. Artedi, Icbthyologia, pt. v. (1738), p. 89. 
’ C. LinmcuB, Svstenia Natura:. 12th edit. 
