72 U.S. NATIONAL MUSEUM BULLETIN 2 02 Vol. 2 



Color tvhen alive. — Top of head and back bright bluish green; a 

 narrow bhie-green line across upper part of eye to snout and a second 

 line from anterior margin of eye just below nostril to snout; lower 

 half of head, sides of body, and belly pure white or grayish white; 

 spiny dorsal smoky purplish; soft dorsal and anal rays dusky, mem- 

 branes faintl}^ yellowish ; upper and lower caudal rays greenish, outer 

 margins blackish, middle rays greenish on scaled portion, yellowish 

 on naked portion, pelvics grayish; pectorals clear hyaline, except 

 upper ray dusky. 



Remarks. — This species may be differentiated from C. caeruleus 

 on the basis of two striking characters: The black axil of the pectoral 

 fin and the greater number of branched pectoral rays (see table 86), 

 usualh^ 17 or 18 in atrip ectoraliSy whereas caeruleus usually has 15 or 

 16. The pectoral axil of caeruleus is pigmented with black dots that 

 form a dusky area only along the dorsal part, thence fading ventrally, 

 where no pigment cells occur, or only a few, whereas atripectoralis has 

 a black axil and the individual black pigment cells are not isolated 

 when viewed under magnification, the outer edge of this black axil 

 sharply contrasts with the pale distal part of the axil. On specimens 

 shorter than about 30 mm. in standard length the axil is not quite 

 as black as in longer specimens. We note that the distal margin of 

 the spiny dorsal fin of atripectoralis may have a duskj^ to blackish 

 line whereas that of caeruleus is pale. 



Although most of the descriptions in the literature for these blue- 

 green damsel fishes fail to mention the colorations of the pectoral 

 axil; some do, and show the spiny dorsal fin with a dark margin. 

 We have listed a few such references in the synonymy. 



Fowler and Bean (U. S. Nat. Mus. Bull. 100, vol. 7, pp. 31, 61, 

 1928) have proposed the subgenus Hoplochromis for C. caeruleus, 

 characterized by having the "front edge of lower jaw with 6 short 

 conic teeth flaring outward." 



Tables 85 and 86 present detailed measurements and counts for 

 certain species of Chromis related to C. atripectoralis. 



CHROMIS DIMIDIATUS (Klnnzinger) 



Plate 83, B 



Heliastes dimidiatus Klunzinger, Verb. Zool.-Bot. Ges. Wein, vol. 21, p. 529, 



1871 (type localitj', Red Sea). 

 Chromis dimidiatus margaritifer Fowler, Proc. Acad. Nat. Sci. Philadelphia, 



vol. 98, p. 140, figs. 9, 10, 194G (type locality, Riu Kiu Islands). 



SPECIMENS STUDIED 



Bikini Atoll: Arji Island, 100 yards off shore, lagoon coral area at depths from 

 to 40 feet, poison and spear, Aug. 7, S-46-308, Brock and Herald, 4 specimens, 

 27.5 to 47.5 mm. 



