CHAPTER XII 

 PERCESOCES AND RHEGNOPTERI 



UBORDER Percesoces. In the line of direct ascending 

 transition from the Haplomi and Synentognathi, the 

 pike and flying-fish, towards the typical perch-like 

 forms, we find a number of families, perch-like in essential 

 regards but having the ventral fins abdominal. 



These types, represented by the mullet, the silverside, and 

 the barracuda, have been segregated by Cope as an order called 

 Percesoces (Perca, perch; Esox, pike), a name which correctly 

 describes their real affinities. In these typical forms, mullet, 

 silverside, and barracuda, the affinities are plain, but in other 

 transitional forms, as the threadfin and the stickleback, the 

 relationships are less clear. Cope adds to the series of Percesoces 

 the Ophiocephalida, which Gill leaves with the Anabantida 

 among the spiny-rayed forms. Boulenger adds also the sand- 

 lances (AmmodytidcB) and the threadfins (Polynemida;} , while 

 Woodward places here the Crossognathida. In the present 

 work we define the Percesoces so as to include all spiny-rayed 

 fishes in which the ventral fins are naturally abdominal, except- 

 ing those having a reduced number of gill-bones, or of actinosts, 

 or other peculiarities of the shoulder-girdle. The Ammodytidce 

 have no real affinities with the Percesoces. The Crossognathida 

 and other families with abdominal ventrals and the dorsal spines 

 wholly obsolete may belong with the Haplomi. Boulenger places 

 the Chiasmodontida, the Stromateidcc , and the Tetragonurid<z 

 among the Percesoces, an arrangement of very doubtful validity. 

 In most of the Percesoces the scales are cycloid, the spinous 

 dorsal forms a short separate fin, and in all the air-duct is 

 wanting. 



The Silversides: Atherinidae. The most primitive of living 

 Percesoces constitute the large family of silversides (Atherinidcz) , 



215 



