180 BRITISH COPEPODA. 
longer than the inner, short and broad, four sete 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 sete; 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 ;';nd of an inch (1'1 mm.). 
Thalestris Clausit was described by the Rev. A. M. 
Norman from specimens found ‘amongst Laminariz 
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. 
