THE FAUNA OF SCOTLAND. 7 



marginal and sub-marginal cellules; the number and position 

 of the recurrent nervures ; the form of the " lanceolate " cellule, 

 (the importance of which is too little known); and the form of the 

 neuration in the posterior wings, and the number of cellules in 

 them. It will depend, however, very much on the group as to 

 what value will be placed on any particular nervures or cellules. 

 Thus among the Nematides the first sub-marginal nervure is often 

 absent, either constantly in particular species or groups, or 

 variable in particular species, and the genus Pristoplwra is 

 founded mainly i^^r^his character, but the absence of this nervure 

 occurs in so many different groups of Nematus, that it loses all 

 generic value. In the same way in some groups, e.g., EmpJiytldes, 

 Selandriades, the fact of there being one or more medial cellules in 

 the posterior wings is not of itself of value, since the dividing 

 nervure is as frequently absent as present in particular species, 

 and again with others the females have a medial cell, while 

 the males have none, (c) The structure of the legs, i.e., whether 

 they are provided with spurs or spines; the formation of the tarsi 

 and trochanters, etc. These are the characters which I consider to 

 be of most importance, and they, moreover, can be seen without 

 dissection. But there are other characters which, in connection 

 with the above, are of great value in defining genera. For 

 instance, the form and position of the eyes, of the clypeus and 

 mouth organs, (the form of the palpi appears to be of little value), 

 of the scutellum and of the thorax generally ; so also the form of 

 the abdomen, and especially the form of the ovipositor. It is 

 difficult to say what value is to be placed on the form and habits 

 of the larvae in respect to the question we are discussing. In 

 some genera the larvae are very useful in this way. Thus, in 

 Dineura {sensu str.), all the larvae are very similar in form and 

 markings, and all feed on the flat surface of the leaf, and hence I 

 hold that this genus should be restricted to the Degeeii group, 

 and the small species at present placed in it transferred to 

 Blennocampa, or to whatever genus they are most nearly related. 



Now in other genera, the larvae vary almost with each species. 

 In Eriocampa, for instance, we have slimeless larvae, slimy larvae, 

 and larvae covered with a white flaky substance. In Nematus 

 again, we have round and flat larvae, elaborately coloured and 

 marked larvae, and others which can scarcely be distinguished 

 from the leaf on which they rest. So also all the larvae of 



