300 U.S. NATIONAL MUSEUM BULLETIN 236 



The carapace has the same pitted structure that is observed also 

 in the female; the cephalic somite, in the region of the oral apertm-e, 

 has a circular hyaline patch in the integument, probably indicating 

 the position of the eye. 



Antennules slightly longer than in female, 6-segmented, subchiroce- 

 rate. No tooth on segment 2, but small, rounded chitinized tubercle; 

 segment 4 big and strongly swollen; apical 2 segments flattened. 

 Setation represented in figure 118a. 



Structure of antenna and mouth parts as in female, not described 

 in detail here. 



There are certain small differences in the structure of the legs 

 (figs. 118c^ though they have the same setal formula as in the female. 



2nd endopodal segment of leg 2 greatly lengthened; internal seta 

 short and strongly haired (fig. 118d). 



Apophysis of 2nd endopodal segment of leg 3 short, differing in 

 small details from that of 0. dubius; external border of 2nd endopodal 

 segment with long spiniform hairs (fig. llSe). 



2nd endopodal segment of leg 4 with long hairs, obscuring presence 

 of 2 setae. Apical seta short, densely haired (fig. 118/). 



5th legs (fig. 118g), as comparison of figures will show, hardly 

 different from those of 0. dubius. Baso-endopodite scarcely elevated, 

 with strong internal and fine external seta. Exopodite well separated 

 from baso-endopodite, with 5 appendages, one of which is strong 

 apical seta. Armature of genital plates composed of 2 setae on each 

 side (fig. 118A). 



Color as in female. 



Remarks. — This new species approaches 0. similis Nicholls, 

 1942a, in many respects, particularly in the furcal structure and the 

 shape of leg 5. There are small differences in setal formulae and no 

 scales appear to occur along the somites in 0. similis. The furcal 

 structure and the peculiar, pitted structure of the carapace make 

 the recognition of this new species fairly easy. It was washed from 

 caulerpas from the reef ridge at Falarik and found in two sand samples 

 taken at various distances from the reef margin at Falarik in the 

 Ifaluk Atoll. 



