36 [February, 



The true Nemocera never have a holoptic head, and hence the 

 differentiation of the sexes in the breadth of the front, and the size 

 and shape of the eyes, if it exists at all, is reduced to a minimum. 

 The eyes round, oval, or lunate, are placed on the sides of the com- 

 paratively very small head, and are separated by a more or less broad 

 front ; when lunate, their upper or lower ends are often approximate, 

 but there is never that broad contact which constitutes a holoptic head. 

 The development of the antennae is large, and, in comparison to the 

 small head, sometimes, we may say, excessive (for instance, in some 

 male Cecidomyiae) ; the contrast in this respect with Bibio and Simii- 

 lium, with their large heads and small antennse, especially in the male 

 sex, is striking. The distinctive character of the antennae of the 

 Nemocera consists in the homology of the majority of the joints of 

 the flagellum ; hence their name (from oiema, thread). Another dis- 

 tinctive character consists in the large development of what we may 

 call sensitive hairs, which adorn the antennae, and are arranged, 

 especially in the male sex, in the shape of verticils, pencils, and plumes 

 (the MycetophilidcB form in this case an exception). The Jegs, 

 although sometimes very long, are generally weak, and but little fitted 

 for walking ; structural peculiarities, useful for classification and de- 

 scription, occur only as exceptions (in Geratopogon, hairy fringes in 

 CTiironomi, &c.). Emjwdia occur, but in rather weak development ; 

 pulvilli seem to be rare (I perceive something like them in some 

 Cliironomi') . 



In general aspect the true Nemocera are distinguished by slender- 

 ness and lightness ; the elongation of the abdomen in comparison to 

 the thorax is especially noticeable (Psychoda, which is more thick-set, 

 forms an exception). Their habits are rather crepuscular ; they prefer 

 shady places and evening hours. Their larvae, peripneustic in the 

 MycetophilidcB and Cecidonujidce, meta- or amphipneustic in the other 

 families, correspond to the two natural sub-groups of the section 

 Nemocera. 



Of course, all these generalities suffer exceptions, but we must 

 bear in mind that the larger the group is which we are considering, 

 the more we must look to the majority of chai-acters only, and the 

 less be embarrassed by exceptions. 



In the five small families, for which I propose to adopt the section 

 Nemocera anomaJa, peculiar structures of the head and eyes sometimes 

 (but not always) occur, which, as far as I know, never appear among 

 the genera of the other Nemocera. Holoptic eyes occur, not only in 



