GENUS NEMATUS. 45 



beyond the middle. In one or two sections (appendi- 

 culatus, Ericlisonii) the first transverse cubital nervure 

 is completely absent. In other species it is often 

 very faint or entirely obliterated in the middle. 



The body is usually smooth, shining, impunctate; 

 in only a few species is the thorax and head punctured ; 

 the body is seldom pilose to any extent. 



The larvae have twenty or only eighteen legs ; when 

 the latter is the number it is the penultimate pair which 

 are wanting. They have mostly cylindrical bodies, but 

 a few which feed on the surface of the leaf are flattish. 

 Many (especially those with gaudily coloured bodies) 

 have glands between the ventral legs from which a 

 fetid odour can be emitted. In habits they vary much ; 

 some are gregarious, others solitary ; most feed ex- 

 posed, while a few live in rolled-down or folded-down 

 leaves, and some of the smaller species raise galls on 

 leaves. The pupa is green, but may also be more or 

 less orange. 



The cocoon is single or double. The eggs are laid 

 singly or in masses on the surface of the leaf, along 

 the midribs or in the twigs; they may be merely 

 glued to the leaf, or more generally they are sunk in 

 the leaf or twigs as the case may be. 



This is one of the largest, and also one of the most 

 difficult genera of the Tenthredinidae. The species 

 differ but little in structural details, there is very little 

 variation in sculpture, the vast majority of the species 

 being smooth and shining, seldom or never punctured ; 

 there is equally little variety in pubescence. In colo- 

 ration there is not much variety either ; the species fall 

 in this respect into five groups : (1) Species with 

 entirely black bodies, and with either entirely or more 

 or less reddish legs, or with white or white and black 

 legs ; (2) black species with the abdomen banded 

 with red ; (3) the black and yellow species, (4) the 

 wholly yellow species, or yellow marked with black, 

 (5) the green species. 



These, however, become mixed the one with the 



