362 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



tractile; maxillary sometimes concealed by preorbital; jaws with, large 

 or small, sharp teeth; vomer and palatine teeth sometimes present; 

 gill openings wide, the membranes separate and free from the isthmus ; 

 gills 4, a slit behind the fourth one; gill rakers long or short, few to 

 rather numerous; scales small, sometimes present only in pectoral 

 region, often forming a corselet; dorsal fins 2, the first composed of 

 rather slender spines, depressible in a groove; second dorsal and anal 

 similar, more or less elevated anteriorly, each followed by about 5 to 10 

 finlets; caudal very broadly forked; ventral fins thoracic, each with I, 

 5 rays; pectorals variable, long or short. 



Six genera are represented in the collections at hand from Peru. 

 Two others, Auxis and Acanthocyhium, each represented by a single 

 species {A. thazard, the frigate mackerel, and A. solanderi, the wahoo) 

 on the American coasts, may be expected in Peru and are included 

 in the key to the genera. The species, if taken, may be identified 

 from the key, and no further mention will be made of them. 



KEY TO THE GENERA 



a. Dorsal fins far apart, distance between them longer than snout and eye; 

 first dorsal composed of 8 to 10 spines. 

 h. Maxillary entirely concealed by preorbital; scales covering entire body. 



Pneumatophorus (p. 362) 

 bb. Maxillary not concealed by preorbital; scales present only on anterior part 



of body, forming a corselet Auxis 



aa. Dorsal fins near each other, the space between them not exceeding diameter 

 of eye, sometimes contiguous; dorsal spines more numerous, rarely fewer 

 than 13. 

 c. Snout of moderate length, much shorter than rest of head, not beaklike; 

 maxillary not concealed by preorbital; first dorsal with 14 to 22 spines. 

 d. Scales present only on anterior part of body, forming a corselet. 



e. Teeth present on jaws only; gill rakers numerous, about 36 to 40 on 



lower Umb of first arch Katsuwonus (p. 365) 



ee. Teeth in jaws and palatines, and sometimes on vomer; gill rakers 



fewer, about 25 to 27 on lower limb of first arch_ Euthynnus (p. 367) 



dd. Scales covering entire body, sometimes enlarged in pectoral region and 



forming a corselet. 



/. First dorsal with 12 to 15 spines; pectoral short or long, equal to or 



longer than head in some species, with 32 to 35 rays- Thtmnus (p. 368) 



ff. First dorsal with 16 to 22 spines; pectoral alwa3's shorter than head, 



with 19 to 24 rays. 



g. Body robust, its greatest thickness much in excess of half the depth; 



palatines with strong teeth; no teeth on vomer; scales enlarged in 



pectoral region, forming a more or less distinct corselet. Sarda (p. 372) 



gg. Body more compressed, its greatest thickness about half its depth; 



vomer and palatines with granular teeth; scales not enlarged in 



pectoral region Scomberomorus (p. 375) 



cc. Snout equal to or longer than rest of head, beaklike; maxillary concealed by 

 premaxiUary; first dorsal with about 26 spines Acanthocybium 



Genus PNEUMATOPHORUS Jordan and Gilbert, 1883 



Head pointed, depressed above; rather robust, not greatly com- 

 pressed, tapering into a slender caudal peduncle; jaws with small 



