BREEDING HABITS OF THE EEL. 443 
The bony fishes date back to the Jurassic period, but did 
not become numerous until the Cretaceous and especially the 
Tertiary Period. The Green River beds of Wyoming abound 
in their remains. 
The Teleosts are divided into eight orders, in an ascending 
series as follows : Opisthomi, Apodes, Nematognathi, Scypho- 
phori, Teleocephali, Pediculati, Lophobranchit and Plectog- 
nathi. 
Order 1. Opisthomi.—The fishes of this group are char- 
acterized by the separation of the shoulder-girdle from the 
head. The ventral fins are either abdominal or wanting. 
The typical genus is Votocanthus, in which the body is elon- 
gated, with a proboscis-like snout. 
Order 2. Apodes.—In this group, also, the scapular arch 
Fig. 400.—Common Eel, Anguilla acutirostria. 
is free from the skull, while the maxillary bones are rudi- 
mentary. The branchial apertures are unusually small, and 
there are no ventral fins, while the body is very long, cylin- 
drical, snake-like. The order is represented among many 
other forms by the common eel (Anguilla), the conger-eel, 
and the Murena of the Mediterranean Sea. The conger-eel 
(Conger oceanicus Gill) ranges from Newfoundland to the 
West Indies. Gill, as well as Giinther and others, regards a 
long transparent ribbon-like fish, described under the name 
of Leptocephalus as the young of the conger-eel. 
The common eel, Anguilla acutirostris (Fig. 400), occurs 
on both sides of the Atlantic, on the North American coast 
as far south as Cape Hatteras, and in inland rivers and lakes. 
The sexes do not differ externally, and internally only 
