1 () A REVISION 01 tin; BRITISH SPECIES OF 



in size from the first to the fifth, which last is scarcely wider than 

 the first abdominal segment. First abdominal segment rather 

 tumid in front, nearly as long as the following three segments, 

 and bearing on each lateral margin in front of the middle a stout 



Seta : holders of the abdominal segments smooth, except the 



last, which is finely pectinated; camlal rami Blender, elongated, 

 parallel, or slightly divergent, about- five times as long as broad, 

 Lateral seta 1 short, considerably removed from the apex; at tho 

 anterior third, on the outer aspect of the ramus, is a transverse 

 row oi* several short, seta 1 , and the inner margins are minutely 

 ciliated ; the outer and inner tail-sct;e are very short, the outer 



rather the shorter of the two ; of the two median seta^ the inner- 

 most is the longer, equalling in length tin 1 entire 1 abdomen ; both 

 are minutely ciliated. Anterior antennas shorter than the first 

 -body-segment. All tho swimming Eeet have both branches three- 

 jointed ; the outer branch o( the first foot has at tin 1 apex of the 

 last joint a single spine and a seta, and on the outer margin one 

 spine; the remaining feet have the same apical armature, but 

 have two lateral spines. The feet of the fifth pair are two- 

 jointed, the basal joint rather wide 1 and bearing at the distal 

 angle one long seta, second joint long and narrow and bearing 

 two apical sctvo, one as long as tho joint itself, the other more 

 than twioe as long. Length 1'55 mm. 



The only British locality known to me for this species is 

 Duddingston Loch, Edinburgh, where it was found by Mr. 

 Thomas Scott, F.L.S., of the Scottish Fishery Board. Ou coin- 

 paring these British specimens with American ones, kindly sent 

 to rue by Mr. B. W. Thomas, I cannot find any great difference. 

 The antennas in the latter are perhaps somewhat longer. 



It is with considerable doubt that I have admitted C. Thomasi 

 as a distinct species. Probably Herrick may be right in looking 

 upon it as a mere variety of the preceding. Hoek, in his figure 

 of the caudal rami of C, bisetosus, gives the characteristic basal 

 row of seta>, though very feebly developed. 



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