l6 VERTEBRATE ANIMALS OF THE UNITED STATES 



basis. Since his death in 1873 the school of ichthyologists founded 

 by him has been directed and carried on by David Starr Jordan, one 

 of his pupils, who together with his pupils and associates has made 

 the fishes of North America better known than perhaps those of any 

 other equally large area. The ^^ Fishes of North and Middle America^' 

 by Jordan & Evermann (i 896-1 900) is the foundation of the descrip- 

 tions of fishes in this book. 



On the Identification of Fishes. — The body of most species of fishes 

 is more or less lenticular in shape and compressed laterally. In many 

 species, however, the anterior portion is cylindrical, as it is in the 

 eel, or more or less depressed (flattened), as in the catfish. The head 

 forms the anterior end of the body, the hinder margin of the opercles 

 marking the boundary between it and the trunk. The caudal or tail 

 fin forms the posterior end, the caudal peduncle being the slenderer 

 portion of the body from which it projects. 



Measurements (Fig. i), — The length of a fish, as given in this book, 

 is the distance between the tip of the snout and the base of the caudal 

 fin, expressed in millimeters: the caudal fin is not included. The 

 measurements of the head and of the depth {i.e., the greatest dorso- 

 ventral measurement) of the body are not given in millimeters or by 

 any other absolute scale, but are relative, being the number of times 

 the length of the body is greater than that of the head or the depth 

 of the body, respectively. Thus, the expression "head 3, depth 5" 

 means that the length of the body is 3 times the length of the head 

 and 5 times its own depth. 



Fins (Fig. i).- — The fins of fishes are of two kinds, the median or 

 vertical fins and the paired fins. The median fins are the dorsal, caudal 

 and anal fins: they are the more primitive of the two kinds, and alone 

 occur in cyclostomate fishes. The dorsal fin lies in the middorsal plane 

 and in many fishes is divided, so that there are two or even three or 

 more of them. The caudal or tail fin is usually the largest and the 

 principal organ of locomotion: its hinder margin may be either forked, 

 concave, emarginate (slightly forked or notched), straight or rounded. 

 In the sturgeon and many other primitive fishes the backbone takes an 

 upward turn at the base of the caudal fin and continues in the fin to 

 near its hinder end, so that the greater part of the fin is ventral to the 

 backbone; such a tail is called heterocercal (Fig. 2). In most fishes, 

 however, the caudal fin is homocercal, that is, the backbone extends 

 only to the middle of the base of the fin, which projects fan-shaped back 

 of it. The anal fin lies in the midventral plane behind the anus; it is 

 in most cases single, but in some species is divided. 



