THE THREADFISHES Family XXVIII. Polynemidae This is a small family of tropical fishes bearing superficial resemblances to the Mugilidae on the one hand and the Scioenidae 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. 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 (Polydactylus virginicus) 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; pectoral with irregular black blotches, the filaments white; ventrals dark, paler on margins. The threadfish (Polydactylus octonemus) occurs along our South Atlantic and Gulf coasts from New York to the Rio Grande. It is rather rare northward, but is more common on the Texas coast. It frequents sandy shores. Colour, light olivaceous, tinged with dark punctulations; belly whitish; pectorals pale in the young, black in the adult. The young of some species of thread-fish, probably Polydactylus octonemus, are common along the Texas coast where they are often seen in large numbers in shallow water on sandy bottom. These fishes vary greatly with age, the pectoral filaments becoming much shorter with age. Polydactylus opercularis is an unimportant species found on our Pacific Coast from Cape San Lucas to Panama. It is generally common and reaches only a few inches in length.