122 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



laterally, fully as broad as pupil at widest point, slightly interrupted 

 on median line; the one on lower jaw similar, though not restricted 

 anteriorly; the band on vomer and palatines continuous, crescent- 

 shaped, of about equal width tlu*oughout, and about as broad as those 

 in jaws; gUl rakers little developed, three small ones on lower and 

 none definitely developed on upper limb, of first arch; upper surface 

 of head smooth; fontanel groove extending forward to opposite an- 

 terior margin of eye and backward nearly to occipital plate; this 

 plate without an evident keel; mandibular barbels small, about equal 

 to space bewteen anterior nostril; maxillary barbels broad, reaching 

 to about middle of anal; origin of dorsal an eye's diameter behind 

 upper anterior angle of gill opening; distance anterior to origin of 

 dorsal 3.3 in length; dorsal spine with a long, flat filament, reaching 

 base of caudal; adipose short and high, over posterior half of anal, 

 its base 5.6 in head; caudal deeply forked, the upper lobe much 

 longer than lower one; anal long, with a rather prominent anterior 

 lobe, its base 1.25 in head; ventral moderately long, reaching a little 

 beyond origin of anal, inserted about equidistant from base of pec- 

 toral and middle of anal base; pectoral spine with a long, broad 

 filament, extending to end of anal base, the spine rough but not 

 barbed along outer margin, 1.6 in head. 



Color bluish above; silvery gray to pale below; dorsal and pectoral 

 largely dusky, with pale filaments; adipose bluish, like the back; 

 upper lobe of caudal dusky, the lower one pale; anal pale, with a large 

 dark area within its anterior lobe; ventral pale, with a large dark area 

 most evident on upper side; pectoral largely dusky, its filament, ex- 

 clusive of its brownish membrane, pale; upper half of maxillary barbel 

 pale, lower half dusky brown. 



The description is based on the only specimen known from Peru, 

 which is 600 mm. (450 mm. to base of caudal) long, taken in the Rio 

 Moche, near Salaverry, by W. L. Schmitt. The long filament at- 

 tached to the dorsal spine, and the dark blotch on the anterior part of 

 the anal readily distinguish this species from B. panamensis. 



Range. — Gulf of California to northern Peru. Previously recorded 

 from only as far south as Guayaquil, Ecuador. 



Genus SCIADES MiUler and Troschel, 1849 



This genus is distinguished from related genera by the enlarged 

 dorsal shield, which often is pointed anteriorly, though sometimes 

 convex to nearly straight, and the occipital shield is scarcely longer 

 than broad. The vomerine patches of teeth are narrowly separated 

 from the much larger triangular patches of palatine-pterygoid teeth. 



Only one species of the genus is known. 



