CHAPTER XXVII 
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 Ophtocephalide, which Gill leaves with the Anabantide 
among the spiny-rayed forms. Boulenger adds also the sand- 
lances (Ammodytid@) and the threadfins (Polynemid@), while 
Woodward places here the Crossognathide. 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 Ammodytide 
have no real affinities with the Percesoces. The Crossognathide 
and other families with abdominal ventrals and the dorsal spines 
wholly obsolete may belong with the Haplomi. Boulenger places 
the Chiasmodontide, the Siromatetde, and the Tetragonuride 
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: Atherinide.—The most primitive of living 
Percesoces constitute the large family of silversides (Atherinide), 
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