A SYNOPSIS OF THE FISHES OF NORTH AMERICA. 



Iclitbyolog^" {r/Ov-^ fish; ^^yo':, a discourse) is the science of fishes. 

 A "fish," in the ijopular sense, is a member of any one of the four classes 

 of aquatic or fish-like vertebrates, the groups here designated as Pisces, 

 ElasmohrancUii, MarsipobrancMi, and Lcptocardii. A fisli, in this com- 

 l)rehensive and somewhat indefinite sense, may be defined as a cold- 

 blooded vertebrate, adapted for life in the water ; breathing by means of 

 gills; having 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 composed 

 of rays connected by membrane. 



Of a "fish" in the poi)ular 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 gi-s-en 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 Bairachia, EejMUa, Arcs, and Mammalia. 

 These four classes have been thus limited and characterized : 



ANALYSIS OF THE CLASSES OF FISH-LIKE VERTEBRATES. 



* Skull uudovcloped, -witli tbe notocliord persistent aiifl extendiug to the anterior end 

 of the head. Braiu not distinctly diU'erentiated. Heart none. 



Leptocardii, 1. 



** Skull more or less developed, with the notochord not continued forward beyond 



the pituitary body. Brain differentiated and distinctly developed. Heart 



developed and divided at least into an auricle and a ventricle. 



t Skull imperfectly developed, and with no lower jaw. Paired fins undeveloped, 



with no shoulder-girdle nor pelvic elements. Gills purse-shaped, 



Marsipobraxciiii, 2. 



ft Skull well developed and with a lower jaw. Paired fins devel()i)ed (sonictinies 



absent through atrophy) ; and with a shoulder-girdle (lyriibrm or furcula- 



shaped, curved forward and with its respective sides connected below), 



an<l with pelvic elements. Gills not i)ui-se-shaped. (Lykifera.) 



Bull. Nat. Mus. No. IC 1 l 



