434 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



reaching a little more than halfway to anal, inserted about equi- 

 distant from base of pectoral and origin of anal; pectoral short, 

 pointed, 1.4 in head. 5.9 in length. 



Color of old preserved specimen brownish above; lighter below; a 

 broad, dark lateral band, about as wide as eye (whether the band is 

 silvery in life is not evident from descriptions) ; dorsals and caudal 

 dusky; other fins pale. 



The Mission did not take this species, and it doubtfully belongs to 

 the marine fauna. It is included here because it has been recorded 

 from Callao, though the specimen upon which that record is based 

 may have been taken in fresh water, where others have been taken 

 as shown by localities cited in the synonymy given at the head of 

 this account. The description is based on a specimen 123 mm. (102 

 mm. to base of caudal) long, taken in the Rio Rimac. The validity 

 of this species was questioned by Jordan and Hubbs (1919), the 

 latest reviewers of the Atherinidae. 



Range. — Streams and possibly the coast of Peru. 



Family POLYNEMIDAE: Threadfins 



Body oblong, compressed; snout conical, piglike, projecting beyond 

 mandible, as in anchovies (Engraulidae) ; eye anteriorly placed, with 

 much adipose tissue in adults; mouth large, nearly or quite horizontal, 

 supplied with bands of small teeth on the jaws, palatines, pterygoids, 

 and sometimes on vomer; gill membranes separate, free from isthmus; 

 gills four, a slit behind fourth; scales on body, head, and usually on 

 vertical fins; lateral line complete, extending on caudal fin; dorsal 

 fins two, well separated, the first with seven or eight flexible spines; 

 caudal deeply forked; anal similar to second dorsal, or longer; ven- 

 trals abdominal, with one spine and five soft rays; pectorals inserted 

 low, in two parts, the lower part consisting of free articulated fila- 

 ments. 



Only one of the two American genera comes within the scope of 

 the present work. 



Genus POLYNEMUS Linnaeus, 1758 



Barbudos 



Margin of preopercle with a scaly flap at lower posterior angle, the 

 margin above it strongly serrate; scales rather thin, ctenoid; second 

 dorsal and anal of nearly equal length, each with about 1 1 to 14 rays. 



KEY TO THE SPECIES 



o. Pectoral filaments 9; origin of anal about under middle of second dorsal; 



scales 67 to 75 opercularis (p. 435) 



aa. Pectoral filaments 6; origin of anal approximately under that of second 

 dorsal; scales 55 to 59 approximans (p. 436) 



