COPEPODA FROM IFALUK ATOLL 23 



endopodal segment doubled, similar spine on 2nd endopodal segment 

 small. 3rd endopodal segment with 4 internal, 2 apical, and 2 ex- 

 ternal setae. 2nd exopodal segment with, well-developed spine at 

 base of internal seta; spine at external margin flanked by two small 

 spines. 3rd exopodal segment with 2 spines at external margin, 4 

 setae at internal margin and at apex with strong apical spine and 

 internal seta. External and apical spmes preceded by smaller spines. 

 Length of apical spine slightly exceeds that of 3rd exopodal segment. 

 3rd exopodal segment of 2nd pair asymmetrically developed; that on 

 left side has structure described above; on right side the 2nd (distal) 

 external marginal spine greatly developed, curved backward (fig. 4c). 

 Endopodite reaches shghtly beyond middle of 3rd exopodal segment. 



Leg 3 as 2nd, with exception of 3rd segment of exopodite, which 

 has 3 external marginal spines. Distinct, slender spine on basis on 

 left and right side of insertion of exopodite. Endopodites and 

 exopodites of nearly same length (fig. 4(/). 



Leg 4 almost as 3rd. No spines occur near insertion of exopodite, 

 but tooth between insertion of endopodite and exopodite well de- 

 veloped. 3rd endopodal segment with total of 7 setae, 3 at internal 

 border, 2 at apex, and 2 at external border. Endopodite and exopo- 

 dite of same length (fig. 4e). 



5th legs complexly built (fig. 2/). Coxae of both sides fused. 

 Right basis more or less triangular, carrying unsegmented endopodite 

 and chelate exopodite, composed of communal segment, carrying 

 articulating external spine, and two blades forming claw. Point of 

 internal blade drawn out in fine filament, basal part with 2 setiform 

 spines. Left basis either completely fused with coxa or of diminutive 

 size. Left endopodite curiously shaped: external border deeply 

 invaginated; apex with 4 setae, with strongly swollen bases, and some 

 spines. Left exopodite with two strong but very unequal marginal 

 spines and 3 curiously formed, lobated appendages representing 

 segments or spines. 



Color completely faded, opaque whitish. 



Remarks. — The present new form is undoubtedly closely allied to 

 P. umbricatus Giesbrecht, from which it easily may be differentiated 

 by the structure of antennules and furca. The asymmetrical de- 

 velopment of the 2nd pair of legs has not been described for any of 

 the previously known species of this genus, but in the present instance 

 it may represent an individual aberration, which I could not check 

 since I had only one individual at my disposal. 



P. 'pacificus undoubtedly inhabits the sandy parts of the reef and 

 its presence in sponge washings must be considered as entirely 

 accidental. 



64&-471— 64 3 



