INTRODUCTION. 29 



in number on each tibia, and occur on all the three pairs of tibice; 

 I have not observed a single case of spurs occurring on one or 

 two pairs of tibite only.^ The last tarsal joints show a sexual 

 character, the very general occurrence of Avhich has, I believe, 

 not been observed before: in the male, the interval between the 

 last and the penultimate joint is excised on the under side, which 

 enables this joint to be bent under the preceding (a similar 

 structure in a Tipula is figured by Westwood in AValker's Ins. 

 Brit. Dipt. Tab. XXYIII, fig. 5 d). In such cases the last joint 

 itself is modified in its structure, generally more elongated, 

 slender, somewhat curved, and beset with bristles on the under 

 side. This structure prevails through nearly all the genera, 

 although it is sometimes wanting in single species of a genus in 

 which it otherwise prevails. 



The prothorax (collare) varies in breadth and the remaining 

 parts of the thorax in shape. These modifications, although 

 mentioned in the descriptions, have not served to establish any 

 important subdivisions. On the front part of the mesonotuni 

 there is often a pair of black dots, one on each side, immedi- 

 ately back of the humerus ; sometimes they assume the appeai*- 

 ance of small pits, with a brown or black, shining bottom. I do 

 not know what they are ; they may have some connection with 

 the prothoracic spiracle, which is not far from them, immediately 

 below. There is no vestige of them in some species and genera 

 (for instance in Pedicia and Amalopis). In other cases, they 

 are quite conspicuous, as in the group of Limnophilae, represented 

 by L. luteipiennis. These latter species have, besides the pits, 

 two closely approximated shining dots, black or brown, near the 

 point of contact of the intermediate thoracic stripe with the 

 collare. 



The abdomen is nine-jointed ; the eighth joint is often narrow ; 

 the ninth usually consists of an upper half segment and of the 

 genitals. The external sexual apparatus of the male consists 

 of a forceps, by means of which the end of the female abdomen 

 is seized from below, a little before the ovipositor, in such a 

 manner, that the latter organ is stretched out on the upper part 

 of the abdomen of the male. This done, the male with a second, 

 inner, clutching apparatus seizes the orifice of the inner genital 



' Atarha may, perhaps, form an exception ; compare this genus. 



