TELEOSTOMI. 25 
Suspotass TELEOSTOMI. (THE TRUE FisHEs.) 
Skeleton usually bony, sometimes cartilaginous. Skull with 
sutures; membrane bones (opercle, preopercle, etc.) present; gill 
openings a single slit on each side; gills with their outer edges 
free, their bases attached to bony arches, normally four pairs of 
these, the fifth pair being modified into tooth-bearing pharyngeals ; 
median and paired fins developed, the latter with distinct rays. 
Ova small; no claspers. Heart developed, divided into an auricle, 
ventricle, and arterial bulb. Lungs imperfectly developed, or modi- 
fied to form a swim-bladder, or entirely absent. 
We here include under one head the Ganoids and the Teleosts. 
The former type is chiefly composed of extinct forms. While 
many of its representatives are extremely dissimilar to the bony 
fishes, there is a gradual series of transitions, and between the 
Halecomorphi of the Ganoids and the Isospondyli of the true 
Teleosts, the resemblance is much greater than that between the 
Halecomorphi and many other Ganoids The Ganoids are, in fact, 
the most generalized of the true fishes, those nearest the stock from 
which the Teleosts on the one hand, and the Dipnoi and Batrachia 
on the other, have sprung. The real value or rank of some of 
the current orders or suborders is still doubtful. (véAeos, perfect ; 
oréua, mouth.) Omitting orders not represented in our waters, 
we have the following analysis of 
Orders of True Fishes. 
w, Arterial bulb muscular, with numerous valves; optic nerves forming a 
solid chiasma; ventrals abdominal; air-bladder with a duct; tail 
strongly heterocercal throughout life; some fins usually with fulcra. 
(Series GANOIDEL.) 
b. Skeleton cartilaginous; ventrals with an entire series of basilar seg- 
ments. (Chondrostei.) 
ce. Maxillary and interopercle obsolete ; skin naked; air-bladder cellular. 
SeLacHostom, VII. 
ec. Maxillary and interopercle present; skin with bony shields; air- 
bladder simple. . . . . + + « « « Guanrostomi, VIII. 
2b. Skeleton bony; ventrals with basitac segments rudimentary; air-bladder 
cellular. (Holostei.) 
d. Vertebra opisthocelian (concavo-convex); maxillary transversely 
divided in several pieces; scales rhombic, enamelled plates. 
GineLymopI, IX. 
