180 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



Seta on proximal segment of fifth legs short; distal podomere a 

 shape different from that of thysanotus, with spinules on inner and 

 outer sides mainly in 2 patches near spines; seta on this segment sub- 

 terminal, only as long as spine on its inner side. 



Sixth legs consisting of 3 setae, borne on a papilla sunk between 2 

 flaps, near middle of genital segment. 



No male has yet been reported. A spermatophore was, however, 

 attached to the genital segment of the female depicted (fig. 4a) ; it is 

 similar to those found in this position on thysanotus. 



Remarks: Williams' description and figures make it relatively easy 

 to identify my specimen with his species in spite of some discrepancies. 

 That of maxillipedal segmentation is probably due to a difference in 

 interpretation; others (such as ciliation of some antennular setae and 

 armature of third antennal, terminal maxillar, and last maxillipedal 

 segments) may be differences in observation ; but the presence of a single 

 element on the mandible can only be explained, in my opinion, by 

 supposing that this appendage was mutilated in his specimen. Since 

 the mouthparts are very difficult to dissect free in poecilostome 

 copepods, and since Williams implied in his description that he was 

 uncertain about the exact relation of parts in this region, this assump- 

 tion does not seem unreasonable. 



Wilson (1932b) did not differentiate his species in any way from 

 adhaerens; nor did he state what features of americanus he con- 

 sidered diagnostic. Examination of his type specimens failed to 

 disclose any evidence for partial fusion of the genital with the first 

 abdominal segment, an additional seta on the second antennal seg- 

 ment, the peculiar ornamentation of the terminal curved setae on 

 the antenna, or the extensive spinulation and fourth spine on the fifth 

 leg. In other respects, his descriptions and figures are close both to 

 Williams' account and my own observations, and the name of his 

 species is thus considered a synonym of adhaerens. 



II. adhaerens is quite distinct from thysanotus as the description 

 above indicates. Its differences from the other species discussed in 

 this paper are considered in the accounts of those species. 



Distribution: Specimens have been found only at Wickford, 

 Rhode Island, and in Chesapeake Bay. None occurred in the only 

 collection made locally for it (p. 162). Correspondence with Dr. C. J. 

 Fish and the presence of a single female in a collection made specifi- 

 cally for this copepod by Drs. Moore and Riser suggest that the 

 species may no longer be abundant in the type locality, or that the 

 proper habitat is still unknown. 



