EXPLANATION OF TERMS AND MEASUREMENTS CXXlll 



are unbranched, membraneless, closely appressed the one to the other, and in 

 ordinary cases not more than half the length of the fully developed rays. This 

 limitation does not, however, apply to the so-called "club-shaped" short first 

 dorsal ray of certain Cyprinidce {Pimephales and Cliola spp.), which is separated 

 from the ray back of it by a well-developed membrane. The last ray of the 

 dorsal and anal fins is often split nearly or quite to the base and appears as two 

 rays, although counted as only one (Fig. 3). In descriptions, Arabic numer- 

 als are used to indicate fin rays and Roman numerals to indicate spines. If a 

 fin contains both spines and soft rays in a continuous series, a comma is 

 used to separate the numerals indicating the two portions, "Dorsal X, 13," 

 for example, indicating a single dorsal fin with 10 spines and 13 soft rays. 

 Two separate dorsal fins are indicated by a dash separating the numerals, 

 "Dorsal X-12" and "Dorsal X-I, 12," indicating respectively: first, a single 

 spinous dorsal of 10 spines followed by a separate soft dorsal of 12 rays; and 

 second, a spinous dorsal of 10 spines followed by a separate second dorsal fin 

 consisting of a single spine and 12 soft rays. 



The height of a fin is measured on the longest ray. 



The length of a fin is measured along its base. 



The origin or insertion of a fin — identical terms — is that of its first ray, or spine. 

 The position of a fin is, technically, the distance from the tip of the snout to the 

 base of its first ray or spine. For example, it may be said of a fish that the 

 "position of the dorsal fin" is contained more, or less, than twice in the fish's 

 length. 



4. The Scales 



The most ready indication of the size of the scales in a fish is furnished by the enumer- 

 ation of the scales in the lateral line, or, if that is absent, of those in a line along 

 the horizontal axis, as nearly as possible, from the upper comer of the gill-open- 

 ing to the base of the caudal rays. It is customary in descriptions to include 

 also counts of the scales in oblique series from the middle line of the back to the 

 lateral line and including it; and the number between the lateral line (not in- 

 cluding it) and the median line of the belly in front of the anal fin. These 

 counts are expressed in a conventional formula, "Scales 6-42-9," for example, 

 indicating 6 scales in an oblique series above the lateral line, 42 in the lateral 

 line (or in a longitudinal series from the gill-opening to the base of the caudal 

 rays), and 9 in an oblique series below the lateral line. 



