A SYNOPSIS OF THE FISHES OF NORTH AMERICA. 
Ichthyology {ixOu~, fish; a discourse) is the science of fishes. 
A “fish,” ill the popular sense, is a member of any one of the four classes 
of aquatic or fish-like vertebrates, the groups here designated as Pisces, 
Elasmohrancliii, Marsipohrancliii, and Lcptocardii. A fish, in this com- 
prehensive and somewhat indefinite sense, may be defined as a cold- 
blooded vertebrate, adapted for life in the water ; breathing by means of 
gills ; ha ving the limbs, if present, developed as fins ; the fingers and toes 
being represented by cartilaginous rays connected by membrane; the 
exoskeleton obsolete or developed as scales or bony plates ; and one or 
more fins developed on the median line of the body, usually comiiosed 
of rays connected by membrane. 
Of a “fish” in the popular sense one could hardly say more, without 
the necessity of the constant introduction of exceptions. Of a “true 
fish,” a fish in a strict zoological sense, — that is, a member of the class 
Pisces, — a definition will be given further on. 
Among the fish-like vertebrates, the writers, following Professor Gill 
and other eminent authorities, recognize four classes, considered as 
co-ordinate with the classes Batrachia, ReptUia, Aves, and Mamhualia. 
These four classes have been thus limited and characterized : 
ANALYSIS OF THE CLASSES OF FISH-LIKE VERTEBRATES. 
* Skull undeveloped, •with the notochord persistent and extending to the anterior end 
of the head. Brain not distinctly dilferenti.ated. Heart none. 
Leptocardii, 1. 
Skull more or less developed, with the notochord not continued forward beyond 
the pituitary body. Brain diftercutiated and distinctly developed. Heart 
developed and divided at least into an auricle and a ventricle, 
t Skull imperfectly develojied, and with no lower jaw. Paired tins undeveloped, 
with no shoulder-girdle nor pelvic elements. Gills purse-shaped, 
AIarsipobranctiii, 2. 
ft Skull well developed and with a lower jaw. Paired tins developed (sometimes 
absent through atrophy) ; and with a shoulder-girdle (lyrifoi-m or furcula- 
shaped, curved forward and with its respective sides connected below), 
and with pelvic elements. Gills not pui'se-shaped. (Lyrifera.) 
BuU. Nat. Mus. No. 1C- 1 l 
