GENUS ENTOMACRODU 



SPRINGER 



21 



erosion) liave removed many of tlie formerly existing islands from 

 the ocean's surface. The Hawaiian Islands (on the periphery), for 

 example, were probably once less isolated than presently. Erito- 

 macrodus species, of that island group, possibly arrived during times 

 of decreased isolation. The species existing there now, well dif- 

 ferentiated from their closest relatives, are either relatively un- 

 changed relicts (of an earlier, more widely distributed species) or 

 more recently evolved isolates. Gosline and Brock (1960) have 

 noted the high percentage of fish species endemic to the Hawaiian 

 Islands and have pointed out that some Hawaiian species are obvious 

 relicts: e.g., Chilorhinus platyrhynchus (Norman), from the Hawaiian 

 Islands and New Britain, both peripheral (the only other species of 

 the genus is in the West Indies); Acanthurus leucopareius (Jenkins) 

 from Hawaiian, Marcus, and Easter Islands, all peripheral; Caranx 

 cheilio Snyder, from Hawaiian and Easter Islands. 



The close relationship of the three endemic Marquesan species of 

 Entomacrodus with nonendemic species and the probably younger 

 age of the Marquesas (high islands), as compared with adjacent 

 island groups (Tuamotus, low islands), tend to indicate relatively 

 recent arrival and divergence of Entomacrodus species in the 

 Marquesas. 



The restriction of E. rofeni, E. stellifer, and E. niuafoouensis to the 

 peripheral area is not so easily explained as are the endemics of the 

 Hawaiian, Marquesas, and Easter Islands. I tentatively believe 

 these three species to be relicts. The disjunct distribution of E. niua- 

 foouensis, at least, would tend to support such a belief. The 

 disjunct distribution (fig. 5) of the Pacific populations of E. decussatus 

 (not peripherally limited) resulting in a group of northwestern and a 

 group of southeastern populations, indicates that E. decussatus 



TABLE 5. --Frequency distribution of number of crenulae on ventral margin of upper 

 lip of certain species of Entomacrodus 



