94 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



(U.S.N.M. No. 127807) about 160 mm. (136 mm. to base of caudal) 

 long, though imperfect in that most of the fins have been more or 

 less injured, and the scales are mostly missing, has been selected as 

 type. The following enumerations and proportions are based on this 

 specimen: D. 12; A. 60; P. 12; scales about 50; ventral scutes 26; 

 gill rakers 8+24. Head m length 5.4; depth 3.4; anal base 1.9; 

 pectoral 5.0. Eye in head 3.3; snout 5.3; maxiUary 2.8; mandible 2.5. 



0. equatorialis differs widely from 0. dovii (Giinther) in the notably 

 smaller head, much more oblique mouth, smaller teeth, more numerous 

 gill rakers, in the presence of a narrow silvery lateral band, and in 

 a number of other respects. In 0. dovii the head is contained 4.3 

 to 5.15 in the length; maxillary 1.95 to 2.2 in head; mandible 1.8 to 

 2.0; gill rakers 7 to 9 + 15 or 16. 0. equatorialis probably is rather 

 nearer to 0. macrops (Giinther), which I have not seen. However, 

 the body seems to be deeper in equatorialis, the head smaller, eye 

 smaller, and the dark humeral spot is absent, whereas a narrow silvery 

 lateral band is present. According to the description by Gilbert and 

 Starks (1904, p. 41) the depth of the body in 0. macrops is contained 

 2% to 3 in the length; head 4% to 4%; eye 2Yz to 2% in the head. 



Range. — Known only from the Gulf of Guayaquil off northern Peru. 



Genus ODONTOGNATHUS Lacepede, 1800 



This genus differs from Opisthopterus principally in the produced 

 maxiUary in the adult, which becomes narrow posteriorly and reaches 

 the gill opening. However, even in small specimens the maxillary 

 is longer and distally narrower than in Opisthopterus. The teeth in 

 the maxiUary are definitely larger and more prominent, with the roots 

 visible in the thin bone. 



ODONTOGNATHUS TROPICUS, new species 



Figure 19 



Head 4.4; depth 3.65; D. 15; A. 48; P. 14; scales lost, about 48. 



Body strongly compressed ; dorsal outline from snout to dorsal only 

 slightly convex, ventral outline anteriorly strongly convex, very 

 slightly concave under pectoral fin, then gently convex; greatest 

 thickness scarcely equal to depth of caudal peduncle; peduncle much 

 shorter than deep, 2.5 in head; head moderately large, its dorsal 

 outline continuous with general outline of back; snout shorter than 

 eye, 3.8 in head; eye 3.1; interorbital 7.5; mouth slightly superior, 

 very strongly oblique; maxillary with strongly convex margin, ex- 

 tending about under middle of eye (the specimen presumably being 

 too young to have this bone prominently produced), 1.5 in head; 

 mandible 1.5; teeth in jaws fairly prominent, very numerous, espe- 

 ciaUy those in maxiUary, with roots visible in the thin bone; gUl 

 rakers at angle about as long as pupU, those on upper Umb very short, 

 8 on upper limb and 20 on lower limb of first arch; ventral scutes 26, 



