PHILIPPINE MACROUROID FISHES GILBERT AND HUBBS. 371 



Sexual dimorphism. — We have been able to demonstrate the ex- 

 istence of sexual dimorphism in this family for the first time. In 

 certain species of C oelorhynchus (C. veUfer and its allies, q. v.) the 

 first dorsal, pectoral, and ventral fins are decidedly longer in the 

 adult males than in the females or the young males. The wide varia- 

 tion 1 in the length of the outer ventral ray in the subarctic Cory- 

 phaenoides cinereus upon reinvestigation is shown to be due likewise 

 to sexual dimorphism : the ray is produced into a long strengthened 

 filament in the male. In most species of the family no marked sexual 

 variation in the length of the fins is evident. 



Age determinatioTis. — We have made a short study of the scales of 

 the species of Gadomus, as presented in more detail under the head 

 of the four species of that genus here reported on. The scales of G. 

 denticulatus especially show certain marks which greatly resemble 

 the so-called " annuli " of certain littoral fishes, and are probably 

 indications of a yearly check in the growth of the fish. These marks 

 are very obscure or entirely absent in the species inhabiting the 

 greater depths. 



Subspecific intergradation. — The intergrading of the geographical 

 subspecies of IlymenoPephalus striatissimus has been w r orked out in 

 detail. So far as known to us this is the first demonstration of its 

 kind among the bathybial fishes. 



Distribution correlated with temperature and depth. — The region 

 of the Jolo or Sulu Sea forms a partly inclosed basin connected 

 with open waters by narrow and comparatively shallow channels; 

 the water of the sea is consequently rendered warm, retaining a 

 temperature of more than 49° F. to depths of over 1,000 fathoms. 

 Though of comparatively small size, the Philippine faunal sub- 

 region, comprising these waters of unusually high temperatures at 

 great depths, contains a large proportion of peculiar and frequently 

 very distinct species, which have probably been evolved in this region 

 of peculiar environmental conditions. The process of their evolu- 

 tion has doubtless been aided or hastened by their isolation, more 

 or less complete, in this partly inclosed sea. 2 



III. THE GEOGRAPHICAL DISTRIBUTION OF THE MACROUROID 

 FISHES OF THE PHILIPPINE AND ADJACENT ISLANDS. 



There are now known about the East Indian and the Philippine 

 Islands no fewer than 75 or 76 species 3 of the Coryphaenoididae. 

 In no other area of similar size is there known a fauna comprising 

 such a numerous and varied assemblage of these fishes. 



1 Gilbert and Hubbs, Proc. U. S. Nat. Mus., vol. 51,-1916, p. 107. 



2 Some of the species range northward to southwestern Luzon. 



3 Including the three subspecies of Hymenoccphalus striatissimus; 69 of these species 

 were obtained by the Albatross. 



