A SYNOPSIS OF THE FISHES OF NORTH AMERICA. 



Ichthyology (l%0u~, fish; Mj-iir, a discourse) is the science of fishes. 

 A "fish," in 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, 

 Elasmobrancliii) Marsipobranchiij 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; 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 popular sense one could hardly say more, without 

 the necessity of the constant introduction of exceptions. Of a "true 

 iish,'' 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 BatracMa, Reptilia, Aves, and Mammalia. 

 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 differentiated. 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, 



MAKSIPOBRANCHII, 2. 



tt Skull well developed and with a lower jaw. Paired fins developed (sometimes 

 absent through atrophy) ; aud with a shoulder-girdle (lyriform or furcula- 

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

 and with pelvic elements. Gills not purse-shaped. (LYRIFERA.) 



Bull. Nat. Mus. No. 1C 1 1 



