THE THREADFISHES 



Family XXVIII. Polynemida 



THIS is a small family of tropical fishes bearing superficial 

 resemblances to the Mugilidce on the one hand and the Scicenidce 

 on the other. They may be distinguished by the abdominal 

 ventrals, the presence of 2 dorsal fins, the anterior of spines 

 only, and by having the lower 5 to 8 rays of the ventral fin 

 detached and filamentous. The family contains 4 genera and 

 about 25 species, only 2 of the former and about 5 of the latter 

 being found in our waters. 



The 2 genera of this family (Polynemus and Polydactylus) 

 both have species in our waters, only those of the latter being 

 of any value. 



Polydactylus differs from Polynemus in the shorter soft dorsal, 

 the serrate preopercle, and the toothed vomer. Numerous species 

 in warm seas, but only 4 within our limits. 



a. Pectoral filaments 6, rarely 5 ; approximans, 261 



aa. Pectoral filaments 7 ; virginicus, 261 



aaa. Pectoral filaments 8 or 9. 



b. Maxillary less than | length of head; pectoral filaments 8; 



octonemus, 262 



bb Maxillary more than % length of head; pectoral filaments 

 usually 9 ; opercularis, 262 



Polydactylus approximans, whose only vernacular name is 

 raton, is found on the Pacific Coast of tropical America from 

 San Diego to Panama. It reaches a foot in length and is a 

 common food-fish at Guaymas, Mazatlan and Panama. 



Colour, yellowish white, darker above; pectoral black in adult. 



The barbudo or barbu (P. mrginicus) is an abundant and 

 useful food-fish, found throughout the West Indies and north to 

 the Florida Keys. About Porto Rico it is common and highly 

 esteemed. It reaches a length of a foot. 



Colour, whitish-olive above, dirty white below; spinous dorsal 

 dark; soft dorsal and anal pale, with dark punctulations; pec- 



261 



