GENERIC AND SPECIFIC DISTINCTIONS. 57 



number of the radial and cubital cellules, the number 

 and position of the recurrent nervures, the form of the 

 lanceolate cellule, the form of the neuration, and the 

 number of cellules in the hind wings. It will depend, 

 however, very much on the group as to what value 

 will be placed on any particular nervure or cellule. 

 Thus, among the Nematina the first cubital nervure 

 is often absent, either constantly in particular species 

 or groups or occasionally with certain species, but its 

 absence occurs in so many widely separated groups 

 that no generic value can be placed on it. In the 

 same way the posterior wings may have either one or 

 no median cellule in different species in a genus, and 

 even in different sexes of the same species, (c) The 

 structure of the legs, i.e. whether they are armed with 

 spurs or spines, provided with patellse or not, the 

 nature of the trochanters, coxae, tarsi, &c. These I 

 consider to be the characters of most value, but other 

 parts of the body occasionally afford distinguishing 

 points. For example, the form and position of the 

 eyes, of the clypeus and other mouth organs, the 

 structure of the thorax and abdomen. In some 

 instances the ovipositor can be used for the same 

 purpose. 



The larvae can be also used in classification. In 

 this respect they are of great value in defining the 

 tribes and subtribes. They do not appear to be of 

 much use with the genera. A few genera, indeed, 

 have well-marked larvae, but in most cases their forms 

 are too much of an adaptive nature to furnish generic 

 characters. Thus, with Eriocampa we have slimy 

 larvae, slimeless larvae, and larvae covered with a white 

 flaky substance. Both Hoplocctmpa and Blennocampa 

 have spiny larvae ; in Nematus they are of all shapes 

 and colours ; while no distinction can be drawn 

 between the larvae of Tenthredo and Allantus or even 

 Dolerus. 



The discrimination of the species is often very diffi- 

 cult. Colour is the distinguishing mark which most 



