172 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



Only the 3 spines nearest base exopodite of first swimming leg with a 

 terminal setule. Base of most median seta on third endopodite seg- 

 ment of legs 2-4 with a group of 3 or 4 strong cilia. Other ornamen- 

 tation as shown in the figures. 



Fifth legs 2-segmented; inserted on ventrolateral corners of thoracic 

 segment. First podomere small and square, almost hidden in dorsal 

 view by a lateral projection (which shows remnant of tergum) of tho- 

 racic segment; its seta, borne on a papilla on outer distal corner, 

 nearly as long as terminal segment. Latter lamellar; with a slight 

 outward and upward curve; bearing 2 spines set stepwise on outer 

 edge of distal half, a long seta on a small papilla and a finely ciliated 

 spine terminally. Terminal segment ornamented with spinules on 

 outer and strong cilia on inner edge. (Several specimens from Puget 

 Sound region have also a "sunburst" of well-developed cilia near base 

 on ventral side.) 



Sixth legs apparently absent. 



Redescription of the male: Body 1.53 mm. in length (mean of 

 6 specimens, range 1.50-1.54 mm.) and 0.65 mm. (0.64-0.70 mm.) 

 wide; paler in color than female. Urosome longer in proportion to 

 prosome and the latter more ovate. Genital segment not compound 

 so that urosome 6-segmented. Paired genital ducts opening ventro- 

 laterally in posterior half of genital segment. Spermatophores (fig. 

 lq) small kidney-shaped structures with a short stalk. (When at- 

 tached to the female, they are rather smaller than indicated by the 

 figure.) Caudal rami shorter in proportion to their width than those 

 of female. 



Ciliated seta on second segment of antennule not as well-developed 

 as in female. 



Antenna occasionally without patch of spinules on inner distal 

 corner of second segment. 



Posterior limit of labium difficult to distinguish; denticles present 

 in female here reduced to small spinules or cilia. 



Mandible and maxillule very similar to female condition, but for- 

 mer may apparently lack second seta on one or other side. 



Figure 3. — a-c, Hemicyclops thysanotus Wilson, female: a, Right second swimming leg with 

 coxal plate, ventral (anterior) view, b, Right third swimming leg with coxal plate, 

 ventral (anterior) view, c, Right fourth swimming leg with coxal plate, ventral (anterior) 

 view, d-j, Hemicyclops adhaerens (Williams), female: d, Left antennule, dorsal (anterior) 

 view, e, Right antenna, ventral (anterior) view. /, Labrum from ventral side but with 

 microscope focused so that dorsal structures are apparent, g, Labium, right paragnath 

 and part of roof of mouth cavity, ventral view, h, Apex of left mandible, dorsal 

 (anterior) view, i, Left maxillule, ventral (anterior) view, j, Distal half of right maxilla, 

 dorsal (anterior) view (flattened, setule-bearing seta partly detached from base). Scale C 

 (fig. 2) applies to c; D to a-b; E to d; F to e-g; and G to h-j. 



