234 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



with a slender spine contained 2.7 to 3.2 in head; pectoral short, 

 scarcely reaching tip of ventral, 1.4 to 1.8 in head, 4.8 to 5.4 in length. 



General color grayish above; silvery below; upper part of side with 

 three longitudinal dark brown stripes, fully as wide as pupil, the lower- 

 most one at about middle of side obscure in some specimens; base of 

 caudal with a prominent black spot; fins all more or less dusky, tip of 

 spinous dorsal and ventral quite dark. 



Ten specimens with more or less damaged caudal fins, about 75 to 

 90 mm. (65 to 74 mm. to base of caudal) long, were secured by the 

 Mission in a rocky inlet in Lobos de Afuera Bay. The largest one 

 (U.S.N.M. No. 127998) has been selected as the type. The following 

 proportions and enumerations apply to that specimen: Head in 

 length 3.1; depth 3.2; fourth dorsal spine 5.7; pectoral 4.95. Eye in 

 head 3.1; snout 3.95; interorbital 5.2; maxillary 2.55; caudal peduncle 

 3.3; fourth dorsal spine 1.8; second anal spine 5.6; ventral spine 2.7; 

 pectoral 1.6. D. XI-I, 18; A. Ill, 18; P. 16; scales 13-69; gill rakers 

 6+16. 



Two small specimens, each 32 mm. long to base of caudal, from 

 Lobes de Afuera (U.S.N.M. No. 77560), identified and listed as Isacia 

 conceptionis by Evermann and Radcliffe, also seem to be of this species. 

 However, the scales are lost, in part, making an accurate count im- 

 possible, and the color has faded, leaving only the black caudal spot 

 visible. 



This species is close to X. xanti Gill (1863a, p. 82), of which no 

 specimens of exactly the same size are available for study. How- 

 ever, in comparing the largest specimen, the type of X. rupestris, and 

 the smallest one of X. xanti at hand, which is 110 mm. (87 mm. to 

 base of caudal) long, and is from Panama Bay, several differences 

 are evident. The differences are set forth in the following compar- 

 isons wherein the proportions are given in percent of the length: 



X, rupestris 



Head deep, rather strongly compressed 

 32.3. 



Eye moderately large, round, not ver- 

 tically slongate, 10.5. 



Interorbital rather broad, transversely 

 convex, 6.2. 



Fourth dorsal spine not reaching origin 

 of second dorsal if deflexed, 17.5. 



Scales in oblique series enumerated just 

 above lateral line 69 (65 to 70 in 10 

 specimens) . 



The color has faded in the smallest specimen of X. xanti at hand, 

 though the dark caudal spot remains. The larger specimens of this 

 species, however, have dark stripes along the upper part of the sides. 



X. xanti 

 Head lower, broader, and longer, 35.6. 



Eye very large, vertically elongate, 



12.0. 

 Interorbital narrower, flat, 5.75. 



Fourth dorsal spine longer, reaching 

 origin of second dorsal if deflexed, 

 19.5. 



Scales lost in type (55 to 62 in 14 other 

 specimens). 



