18 U.S. NATIONAL MUSEUM BULLETIN 236 



side formed as clasping antennule. Segments of left antennule 

 notably thick, with the exception of ultimate and penultimate seg- 

 ments, which are slender. Setation of antennule represented in figure 

 3a; setation of segments 2-14 uniform, composed of two setae, one 

 small, one large. 1st segment much larger than following segments, 

 with 3 sets of each 2 setae. In addition, there are 2 aesthetascs. 

 Segment 15 with 1 seta at external border; segment 16 with large 

 seta at external border and a smaller seta at internal border. Segment 

 17 with internal and external apical seta; ultimate (18th) segment 

 with internal and external marginal seta and 5 apical setae, one of 

 which has a swollen base and resembles an aesthetasc. Proportional 

 lengths of the antennular segments: 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 



140 30 30 30 20 30 30 30 40 40 40 50 60 40 60 80 130 120=1,000. 



Right antennule shaped as clasping organ, hinge developed between 

 14th and 15th segments (fig. 36). My preparation proved to be 

 unsatisfactory for studying the setation of this appendage. Spines 

 on 15th and 16th segments: that on 15th small and externally directed, 

 that on 16th stronger and internally dii'ected. Setae of antennules 

 nude. 



Preparation of antennae unsuccessful; exopodites of both sides be- 

 came detached during preparation (fig. 3c). Coxa small, without 

 seta, almost fused with much larger, elongate basis, with single seta 

 at apex of internal margin. 1st endopodal segment elongate, with 

 one internal seta at % of border from apex. 2nd endopodal segment 

 very elongate; apical part, apparently representing external lobe and 

 carrying 6 marginal setae and 1 appendicular seta, articulating with 

 rest of segment. That part of 2nd endopodal segment with 4 mar- 

 ginal and 3 terminal setae. 



Cutting edge of mandibular praecoxa in unfavorable position in my 

 preparation, with the result that it could not be studied. Coxa small, 

 basis much larger, elongate, with single seta at internal margin. 

 Endopodite 2-segmented, 1st segment small, with 3 subapical setae; 

 apical (2nd) segment large, with 8 marginal setae and 1 appendicular 

 seta. Exopodite small, apparently 4-segmented, basal 3 segments 

 each with remarkably strong, densely plumose seta; apical (4th) seg- 

 ment with 3 smaller, plumose setae (fig. 3d). 



Figure 2. — Pseudocyclops pacificus, new species, loc. 709, ad. cT, holotype: a, whole animal, 

 dorsal view; b, same animal, lateral view from right side; c, distal part abdomen and furca, 

 dorsal view; d, idem, lateral view from left side; e, head, lateral view from right side, 

 antennules removed;/, 5th legs, (a, b, X 100; c, d, X 275; e, X 145;/, X 460.) 



