INTRODUCTION. 
IX 
Isospondylous Scopelidac or to the Acanthoptcrygian Berycid®. 
One very abundant family, that of the Enchodontid®, might perhaps 
furnish the ancestors of both. These exclusively Cretaceous fishes 
are Scopeloids, in which the premaxilla has not completely excluded 
the maxilla from the tooth-bearing margin of the jaw. They are 
variously specialised by the development of large teeth and dermal 
scutes ; and two of them ( Eurypholis and Prionolepis ) are provided 
with a formidable spine at the angle of the preoperculum — a feature 
unknown among existing physostomous fishes. The stoutness of 
their bones indicates that they lived in shallow water or at the 
surface of the ocean during the Cretaceous period; while their 
nearest allies at the present day — the Odontostomidse and Alepi- 
sauridaa — are all denizens of the deep sea. 
Of the family Seopelidae many of the Cretaceous representatives 
scarcely differ from genera widely distributed in existing seas. 
The only remarkable Cretaceous forms — and those provisionally 
placed here — are two genera in which the stout premaxilla forms 
a pointed rostrum. These are Apaleodus and Bhinellus ; the former 
with a short snout, the latter with so slender a rostrum that a very 
superficial study of the fish has caused it hitherto to be erroneously 
classified with Btloru and the Scombresocid®. 
The Gonorhynchid® are only slightly modified Scopeloids, and 
are now shown to date back to the Cretaceous period, when all the 
characteristic features of Gonorhynchus, except the extension of 
scales over the head, seem to have been already acquired. The 
discovery of an early Tertiary freshwater genus ( Noloyoneus ) both 
in North America and Europe, is one of considerable interest. 
Other modified Scopeloids seem to be recognisable among Cre- 
taceous fishes, but their osteology is as yet imperfectly known. 
The remarkable extinct “ flying fishes ” of the family Chirothricid® 
may probably be thus interpreted. 
The Esocidae are essentially freshwater Scopeloids, and the 
Cyprinodontid® are generally admitted to be closely allied to this 
family. Nothing of importance is known concerning their geolo- 
gical history. 
OsTARIOPHTSI. 
The past history of all freshwater fishes is very imperfectly 
known. Freshwater deposits are of such limited extent that they 
rarely escape denudation for long geological periods ; and, except 
perhaps from a few sediments deposited at the mouths of rivers, 
