56 PEECES0CE3. 



Sub-order III. PERCESOCES. 



The Fishes of this sub-order differ from the Acanthopterygii in the abdominal 

 position of the ventral fins, the pelvic bones not being directly attached to the clavicles. 

 In all the American species there are two well-separated dorsal fins, the first of which 

 is formed of from 3 to 9 spines, the second of a spine and 7 to 15 articulated rays. 

 The anal fin is wholly or partly opposed to the second dorsal and has from 1 to o 

 spines. The ventral fins are inserted well behind the base of the pectorals; each 

 consists of a spine and 5 branched rays. The caudal fin is forked. 



Each of the four families is marine and widely distributed. The majority of the 

 species are shore-fishes which frequent the mouths of rivers and sometimes ascend 

 into fresh water. The Atherinidae and Mugilidae include a number of permanently 

 fluviatile forms. 



Synopsis of the American Families of the Suh-order Percesoces. 



I. Lateral line usually absent, never complete ; pectoral fins placed liigli. 



Anterior dorsal of 3 to 8 slender s])ines ; a single anal spine; vertebrEe 



32 to 60 1. Atherinid^. 



Anterior dorsal of 3 to 5 pungent spines ; 2 or 3 anal spines; vertebrae 



24 to 2G 2. MuGTLiDJi:. 



II. Lateral line present, complete ; pectoral fins placed low. 



Pectoral fin normal . 3. Sphyr^enidjs. 



Pectoral fin with a detached lower portion composed of free filamentous 



rays 4. Polynemid^. 



ram. 1. ATHERINIDiE. 



The Atherinidse occur on the coasts of most tropical and temperate seas ; a consi- 

 derable number of them enter or permanently inhabit fresh waters. Those found in 

 the rivers and lakes of Mexico and Central America have the following features in 

 common : — Body elongate, more or less compressed. Lateral line usually absent, 

 never complete. Two well-separated dorsal fins, the first formed of 3 to 6 slender 

 spines, the second of a short spine and 7 to 13 articulated rays. Anal with one 

 spine and 12 to 25 articulated rays. Pectorals placed liigh ; ventrals abdominal, each 

 with one spine and 5 branched rays. Caudal forked. Prfemaxillaries protractile ; 

 jaws with two or more series of conical teeth ; palate tootliless, or a few teeth on 

 the vomer. A silvery lateral longitudinal band or stripe always present. 



