320 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



Color brownish, with a shght silvery sheen, especially on lower part 

 of side; sides with five dark vertical bars, and with a suggestion of a 

 sixth one at base of caudal, the first one crossing eye, the second 

 crossing base of pectoral, the third narrower than the others, extending 

 down from fourth dorsal spine and disappearing behind base of pec- 

 toral; the fourth extending from posterior spines of dorsal to base of 

 anterior rays of anal ; and the fifth extending from near midlle of soft 

 dorsal to somewhat posterior to middle of anal; dorsals and anal 

 brownish, with dark margins; caudal brownish at base, rest of fin plain 

 translucent; ventral very dark brown; pectoral brownish at base, the 

 rest of fin plain translucent. 



The description is based on a small specimen, 68 mm. (52 mm. to 

 base of caudal) long, dredged near Sechura by the Mission. As far as 

 known, this is the first and only representative of the genus taken in 

 Peruvian waters. This fish agrees well with a specimen from Guay- 

 aquil, and several from Panama Bay and the west coast of Central 

 America and Mexico with which it was compared. In large individ- 

 uals the interorbital becomes considerably expanded, the scales cover 

 all the fins, and the anterior rays of the second dorsal, as well as those 

 of the anal become greatly produced, and the outer rays of the caudal 

 become elongate, making the margin of the fin concave. 



Range. — California to northern Peru. Previously reported from 

 only as far south as Guayaquil, Ecuador. 



Family CHAETODONTIDAE: Butterflyfishes 



Body short and deep, usually strongly compressed; head short, 

 mouth small, terminal; premaxillaries protractile; teeth bristlelike, 

 in a band in each jaw, none on vomer or palatines; gills 4, the rakers 

 short or obsolete, the membranes united with the isthmus; pseudo- 

 branchiae large; scales rather small, ctenoid; lateral line more or less 

 concurrent with the back; dorsal fin single, the soft part often elevated 

 anteriorly, generally densely covered with scales; anal with 3 or 4 

 spines, the soft part usually similar to that of dorsal; ventral thoracic, 

 with I, 5 rays. 



A single genus and species, new to the fauna of Peru, comes within 

 the scope of the present work. 



Genus CHAETODON Linnaeus, 1758 



Body ovate, strongly compressed; snout more or less pointed; mouth 

 very small, terminal; teeth in jaws small, flexible, numerous, in bands; 

 preopercle without an enlarged spine; lateral line arched; scales firm, 

 ctenoid, about 30 to 50 in a lateral series; dorsal fin long, continuous, 

 with about 11 to 15 spines, the anterior ones longer than some of the 

 posterior ones; soft part rather low, with about 18 to 21 rays; caudal 



