180 BRITISH COPEPODA. 



longer than the inner, short and broad, four setae on 

 the outer margin, one long plumose apical seta, and one 

 short seta on the inner margin ; inner branch bearing 

 three strong, sub-equal, spine-like setae ; caudal seg- 

 ments short and broad ; internal seta as long as the 

 abdomen, external about half as long; in the female 

 swollen at the bases, but not so in the male. 



Length - 2 ^-nd of an inch (1*1 mm.). 



Thalestris Clausii was described by the Rev. A. M. 

 Norman from specimens found " amongst Laminariae 

 in Bressay Sound, 1867 ; and also at Tobermory, in the 

 Isle of Mull, in 1866." It occurs also in gatherings 

 made recently by Mr, Norman at Oban. It is, in fact, 

 one of the commonest, perhaps the commonest, British 

 species of Thalestris, often occurring plentifully in the 

 littoral zone amongst weeds, and not unfrequently in 

 the open sea, where it is taken by the surface-net. In 

 such situations I have found it frequently on the 

 Northumberland and Durham coasts; in Birtirbuy, 

 Clifden, and Westport Bays (Ireland), the Scilly 

 Islands, and Cumbrae (Firth of Clyde). 



The characters, on the strength of which this 

 species was separated from the rest of the genus, are 

 certainly insufficient ; I therefore here return to the 

 old generic term. 



