billabong at Oenpalli on tihe Alligator River, Arn- 

 hem Land, Australia. Holotype female (USNM 

 125681) and 35 paratype females (USNM 125682). 



Female. — Body form as in figure 26. Total 

 length 725 /*. Greatest width 295 ,x. measured at 

 widest part of posterior portion of cephalon. Ceph- 

 alon subdivided as in E. coleus, but posterior lobe 

 bearing mouth parts and first thoracic legs only. 

 Thoracic segments bearing legs 2, 3, 4, and 5 free. 

 Genital segment (fig. 27) as wide as long (81 ^ by 

 81 n) . Abdomen 3-segmented, each segment some- 

 what narrower than preceding. Caudal rami short, 

 inner distal corner produced to form stout spine- 

 like process; each ramus with three additional 

 setae. 



First antenna (fig. 28) 6-segmented and armed 

 as in figure. Second antenna (fig. 29) 4-seg- 

 mented; second segment enveloped in a thin 

 sheath, surface of sheath somewhat wrinkled in 

 appearance (not as much as in E. coleus). Second 

 antennae completely encircle a gill filament of 

 host. Mouth parts as in previous species. Maxilli- 

 peds absent. 



Legs 1 to 4 biramose. Leg 1 (fig. 30) rami 3- 

 segmented, armed as in figure. Leg 2 (fi^. 31) 

 rami 3-segmented, armed as in figure. Leg 3 simi- 

 lar to leg 2 except last exopod segment with six 

 setae and last endopod segment with four setae 

 and one spine. Leg 4 (fig. 32) exopod 2-segmented ; 

 endopod 3-segmented, armed as in figure. Spine 

 and seta formulas for legs 1 to 4 follow : 



Leg 5 (see fig. 27) a free segment bearing two 

 terminal setae — one subterminal and one near base 

 of free segment. Leg 6 absent. 



Egg sacs 500 fx. long and containing 25 to 30 eggs. 



Color in life unknown. 



Male. — ^Unknown. 



Etymology. — The specific name semicoleus is 

 Latin for "half sheath" and refers to the nature 

 of the second antenna. 



Remarks. — ^This species differs from all other 

 known species in having half of the second antenna 



encased in a sheath. It seems to be closely related 

 to E. coleus and E. am/plectens based on the pres- 

 ence of this sheath and other characters common 

 to all three species. 



Ergasilus inflatipes Cressey, New Species 

 Figures 33 to 41 



Specime^is studied. — ^Three collections contain- 

 ing 28 females from Strongylura senegalensis from 

 the Volta River, Ghana, and a single collection 

 with 33 females from the same host from Ebzie 

 Lagoon, Ivory Coast. Holotype female (USNM 

 125683) and 8 paratype females (USNM 125684) 

 from one of the Ghana specimens. 



Female. — Body form as in figure 33. Total 

 length 625 /x. Greatest width 354 ^ measured at 

 widest part of cephalon. Cephalon not subdi\nded 

 dorsally as in previous two species. Thoracic seg- 

 ments bearing legs 1 to 5 free, each one narrower 

 than preceding segment. Genital segment (fig. 34) 

 slightly wider than long (88 /t by 74 /x). Abdomen 

 (fig. 34) 3-segmented; anterior two segments each 

 with two interrupted transverse rows of spinules 

 and last abdominal segment with a row of fine 

 spinules along posterior border, all on ventral sur- 

 face. Caudal rami short, about as wide as long and 

 bearing four setae, innermost considerably longer 

 and wider at base than other three. 



First antenna (fig. 35) 6-segmented; first two 

 segments incompletely divided, each segment 

 armed as in figure with a plumose seta present 

 on each of the last three segments. Second antenna 

 (fig. 36) in shape of claw with no distinguishing 

 characters. Mouth parts as in figure 37 ; mandible 

 with single seta near base, of terminal process; 

 first maxilla a small lobe with three setae; second 

 maxilla with single seta on terminal segment near 

 base of spinose tip. Maxillipeds absent. 



Legs 1 to 4 biramose. Leg 1 (fig. 38) rami 3- 

 segmented, armed as in figure. Leg 2 (fig. 39) rami 

 3-segmented; coxopod with rows of fine spinules; 

 rami with spines and setae as in figure. Leg 3 

 identical to leg 2. Leg 4 (fig. 40) exopod 2-seg- 

 mented ; endopod 3-.segmented ; rami armed as in 

 figure. Leg 5 (fig. 41) with free segment bearing 

 three setae, outer two plumose; single seta near 

 base of free segment. Leg 6 absent. 



356 



U.S. FISH AND WILDLIFE SERVICE 



