NO. 3582 GENUS ENTOMACRODUS — SPRINGER 13 



7. decussatiis group (E. decussatiis, E. iifrmiculatiis). Largest 

 species, having the upper Up completely creiiulate in adults, generally 

 high meristic counts, dorsal fin attached at, or posterior to, the caudal 

 base. Indian, central and western Pacific Oceans. 



Zoogeography. — Some aspects of this topic are discussed under 

 the individual species accounts (see especially "Relationships" under 

 E. chiostictus) . There is a decreasing number of species of Ento- 

 macrodus in the various oceans as one progresses westward from the 

 central Pacific Ocean around the world to the eastern Pacific Ocean 

 (table 6) . If one subscribes to the hypothesis that the center of origin 

 of a particular taxonomic group is the area where the most species of 

 that group occur, then the central Pacific Ocean is the area of origin of 

 Entomacrodus. The central Pacific is also the only area where as 

 many as six species (fig. 3) have been taken at a single locality. 

 Ekman (1953, p. 18) has stated that the Indo-Malayan (Indonesian) 

 region (here comprised of portions of the Indian Ocean and western 

 Pacific areas of table 6) is the area from which adjacent regions 

 derived their marine shore faunas; however, Ladd (1960), on the 

 basis of geologic evidence, fossil molluscan faunas, and present 

 meteorological conditions, postulated that the Indonesian areareceiv^ed 

 its marine shore fauna by invasion from the central Pacific Ocean. 

 Actually, the distribution of the species of Entomacrodus does not 

 support an Indonesian origin as opposed to a central Pacific origin 

 of the genus. If one eliminates from consideration the isolated 

 island species of Entomacrodus, there are eight species found in the 

 central Pacific and probably eight occurring in Indonesia (assuming 

 that E. niuafoouensis, which has been recorded from the Indian and 

 western Pacific Oceans but not Indonesia, probably does or did occur 

 in Indonesia). There are six species common to both areas; this 

 leaves two species in each area which do not occur in the other. 



None of the areas of table 6 have representatives of all the species 

 groups of Entomacrodus. The eastern Pacific and eastern and west- 

 ern Atlantic are all occupied by the same group, nigricans. The 

 Indian ocean has four groups, and the central and western Pacific 

 areas each have six groups. The central and western Pacific areas 

 together have all seven groups. In spite of the lack of definitive data 

 to support a contention that some portion of the Old World tropical 

 Pacific is the area of origin of Entomacrodus, I find it difficult to 

 believe otherwise. 



Nine of the 15 central and western Pacific Ocean species of Ento- 

 macrodus have their entire distribution either along or near a line 

 circumscribing the periphery of the tropical-subtropical portions of 

 the area (fig. 4: the basis for the construction of the line is the distri- 

 bution of the Pacific coral reefs as given by Wells, 1957, except that 



