144 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Suborder RHEGNOPTERI. 
Aetinosts of pectoral fin of 3 forms, 2 of them normal, supporting the pectoral fin, one of them 
longitudinal, without rays, and the fourth a plate on the coracoid, supporting 3 to 10 free and separate 
rays or feelers; post-temporal and shoulder-girdle normal; vertebrae 10 + 14 = 24; 2 separate dorsal 
fins, the first of a few spines; pseudobranchiae concealed; ventrals subabdominal, behind pectorals. 
One family, Polynemidiv, of uncertain origin and affinities. 
Family XLV1I. POLYNEMID.F. —The Threadfins. 
Body oblong, compressed, and covered with rather large, loosely inserted, ctenoid scales; lateral 
line continuous, continued on the tail, usually forked, with a branch on each lobe; head entirely scaly, 
snout more or less conical, projecting over the mouth, which is rather large, inferior, with lateral 
cleft; premaxillary protractile, its basal process vertical; maxillary without supplemental bone, 
extending much beyond the eye, which is anterior, lateral, rather large, with a well-developed adipose 
eyelid; villiform teeth on jaw's, palatines and sometimes on vomer; pseudobranchise concealed; 
hranchiostegals 7; gill-membranes separate and free from the isthmus; gills 4, a slit behind the fourth; 
2 separate dorsals, somewhat remote from each other, the first of 8 feeble but rather high spines, the 
first and last spines very short, the third longest; the second dorsal of soft rays only, equal to first in 
height, but with base somewhat longer; anal fin either similar to or much longer than soft dorsal; 
caudal fin rather long, widely forked; second dorsal, anal and caudal fins more or less covered with 
small scales; the first 3 or 4 dorsal spines winged; ventrals i, 5, abdominal, but not far removed from 
pectorals; pectoral fins moderate, placed low, in 2 parts, the lower and anterior portion of several fili¬ 
form articulated appendages free from each other, used as organs of touch. In the young, the dorsal, 
caudal, and pectoral fins are dusky, the anal and ventral fins white; all the fins grow darker with age, 
the pectorals usually becoming black, the opercle blackish. Bones of the skull with a well devel¬ 
oped mueiferous system as in Sckmukr. Basis eranii double, with muscular tube; post-temporal bifur¬ 
cate; hypercoracoid with median foramen; superior pharyngeal bones 4; pectoral aetinosts divided, 2 
of them normal, supporting the pectoral fin, 1 longitudinal without rays, and 1 a plate on the coracoid, 
supporting the pectoral filaments; stomach caecal with many pyloric appendages; air-bladder various, 
sometimes wanting; vertebrae 10 ; 14=24. Genera 4, species about 25, inhabiting sandy shores of 
tropical seas, and sometimes entering rivers. .Most of them are valued as food-fishes, their flesh being 
like that of the (jc.umuhr. The relations of this peculiar family appear to be with the Sciacnidx on the 
one hand, and with the Mugilidx on the other, but all these resemblances may be superficial. 
Genus 86. POLYDACTYLUS Lacepede. 
Anal fin not much longer than soft dorsal, of about 13 or 14 rays; vomer with teeth; free filaments 
of pectorals mostly shorter than body; teeth in villiform bands on both jaws, vomer, palatines, and 
pterygoids; preopercle sharply serrated on its posterior margin, its angle with a scaly flap; scales rather 
small, finely ctenoid; first dorsal with 7 or 8 feeble, rather high spines, the first and last short; soft 
dorsal and anal fins about equal; pectoral filaments 3 to 9; pyloric cueca in great number. Species 
numerous, in warm seas. 
Pbl/ldaclylus l.acepude, Hist. Nat. I'oiss., VIII. 181, 1832 (plumicri—virginicus). 
Polynemus Gunther, Cat., II, 319, 1860 ( microstoma ); not of Linnaeus. 
102. Polydactylus sexfilis (Cuvier & Valenciennes). “Moi;” “Moi-lii 
Head 3.3 in length; depth 3.5; eye 4 in head; snout 5.5; maxillary 2.2; interorbital 3.6; preorbital 
2.75 in eye; I*, vim, 13; A. in, 11; scales 8-66-12; third dorsal spine longest, 1.4 in head; ray 1.4; 
longest anal 1.6; 6 pectoral filaments, longest 3.1 in body; pectoral ray 1.5 in head; ventral 2.1; caudal 
peduncle 2; distance from anterior base of soft dorsal to upper edge of gill-opening equal to distance 
from same base to base of caudal fin; this last distance equals distance from posterior base of soft dorsal 
to fork of caudal fin; distance between anterior bases of dorsals equaling distance from anterior base 
of spinous dorsal to posterior edge of eye; base of soft dorsal slightly greater than base of anal. 
