162 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



narrowed distally, as long as the plumose seta on the second seg- 

 ment; spermatophore sausage-shaped. Total length, 1.25-1.5 mm. 



Male. — Urosome 5-segmented, but the penultimate segment is very 

 short and often poorly defined ; genital orifice on left side ; fifth legs 

 made up of a compion median piece, the fused first basipods, a right 

 ramus, 4-segmented, and a left ramus, 3-segmented; end segment of 

 right leg claw-shaped, swollen in the middle, and forming an imper- 

 fect chela by shutting against a wide process on the inner margin of 

 the penultimate segment. Total length, 1-1.15 mm. 



Reinarhs. — ^Wlieeler's statement that this is one of the commonest 

 copepods at Woods Hole during the summer months still holds true. 

 From the list of localities within the present area where it has been 

 found it is evident that the species can adapt itself to any degree of 

 salinity. Its presence in such fresh-water lakes as John Pond and 

 Barnstable Great Pond suggests an ability for active migration up 

 the rivers forming the outlets to such ponds. A careful comparison 

 of structural details and a series of measurements of specimens taken 

 from fresh, brackish, and salt water, like those made by Ekman for 



Lminocalambs grimaldii and 

 L. maci'urus'^ would undoubt- 

 edly yield interesting results. 



ACARTIA BIFILOSA (Giesbrecht) 



Figure 110 



Bias Mfilosus Giesbrecht, Zool. 

 Anz., vol. 4, p. 257, 1881. 



Acartia hifilosa Giesbrecht, Fauna 

 und Flora des Golfes von Nea- 

 pel, vol. 19, p. 507, pi. 43, 1892. 



Occurrence. — Surface tow, 

 Vineyard Sound, December, 

 1887; recorded by Fish as 

 common in Woods Hole Har- 

 bor from December to June. 

 Distribution. — British seas 

 (T. Scott, Brady) ; Mediter- 

 ranean (Giesbrecht) ; Skager 

 Kak (Cleve) ; tropical and 

 northern Atlantic (Cleve) ; Helgoland (Glaus, Timm) ; coast of 

 Norway (Boeck) ; Baltic Sea (Lindstrom). 



Color. — Body colorless and transparent with just enough of a 

 whitish tinge to make the copepod visible over a dark background. 



Female. — Corners of fifth segment rounded, without spines; 

 urosome about one-third the length of the metasome ; dorsal surface 



Figure 110. — Acartia hifilosa: a. Female, dor- 

 sal (after Giesbrecht) ; ?j, female, fifth legs ; 

 c, male, fifth legs 



' Intemat. Rev. Ges. H. und H., vol. 6, p. 355, 1913, 



