MARINE AMPHIPODA IN MICRONESIA — BARNARD 533 



having lageniform ejes but head lobes intermediate in shape between 

 E. afer and E. atlanticus. Provisionally these specimens have been 

 assigned to E. pacificus Schellenberg (193Sa), a species described as 

 having the eyes and head lobes of Stebbing's E. atlanticus but ex- 

 hibiting quantitative gnathopodal differences. The gnathopods are 

 smaller in both sexes, with the male second gnathopodal finger over- 

 lapping the less oblique palm and the female gnathopod lacking the 

 definition seen in E. atlanticus. Schellenberg did not figure the head 

 and eyes. The head lobes of the present specimens are clearly dis- 

 cernible from those of E. atlanticus and E. afer as described by Stebbing 

 but approach closely Pillai's figure of the head of E. afer. 



Another species, Eurystheus imminens K. H. Barnard (1916 and 

 1937), is probably a mutant of E. atlanticus and is based on a slight 

 difference in palmar tooth structure of the male second gnathopods. 



If the specimens herein assigned to E. pacijicus are really what 

 Schellenberg described, then Micronesia supports a mutant form of 

 E. atlanticus and a distinct but close relative, E. pacijicus, bearing 

 close resemblance to E. afer, because of its intermediate head and 

 eyes. 



Probably a complex of specific populations exists, each maintaining 

 separation in different geographical areas but assuming different 

 morphological appearances in distantly separated regions. Simply 

 stated, species A in area 1 approaches the morphology of species B 

 in area 2 but species B in area 1 is quite distinct from species B in 

 area 2 ; hence, it differs notably from species A. 



The genus Audulla was described originally by Chevi'eux in the 

 family Ischyroceridae but Stebbing (1906) correctly listed it as a 

 photid. In the Photidae, Audulla chelifera, the type species, keys 

 out to the genus Eurystheus Bate. A comparison of A. chelifera with 

 Eurystheus maculatus (=E. tridentatus) , the type species of Eurystheus, 

 shows that male Audulla differs from male Eurystheus by the following 

 characters: the stouter second antennal flagellum, the very short fifth 

 article of gnathopod 2 and the transverse semichelate palm of gnatho- 

 pod 2. Since 1901 a number of species of Eurystheus have been 

 described carrying a second gnathopod approaching the transverse 

 palm and even the semichelate condition of Audulla. The condition 

 in Audulla might be interpreted as a coarse defining tooth with a 

 medial excavation which, in a qualitative sense, is scarcely different 

 from some of the following species: Eurystheus Una, E. semichelatus, 

 E. crassipes, E. chiltoni, E. longimanus, E. scissimanus, and E. abyssalis. 

 The following three species have a shortened fifth article of gnathopod 

 2: E. anamae, E. ostroumowi, and E. lobatus. The gnathopods of E. 

 semichelatus and E. Una are notably similar to Audulla; hence, 

 only the stoutness of the second antennal flagellum remains as a 



