270 



joining the auxiliary and 1st longitudinal veins ; it is absent in 

 PTYCHOPTERIXJE and TIPULIN.E. The marginal cross-vein is 

 absent in TIPULINJE, present in many genera of LIMNOBIIN^E, but 

 varying in position and intensity, its presence not always constant 

 in the same genus; its value as a generic character must be 

 regarded as comparatively small. The costal cross-vein is a term 

 herein proposed for the small cross-vein joining the costa to the 

 1st longitudinal nearly at its tip, just before it turns down into 

 the 2nd vein or the anterior branch of the latter. The discal 

 cross-vein is the short veinlet uniting the upper and lower branches 

 of the 4th vein, closing the discal cell and forming its distal side. 

 The anterior cross-vein is nearly always present, being absent 

 in Mongoma, and is nearly always placed over the discal cell, 

 when such is present, joining the 3rd and 4th longitudinal veins. 

 Posterior cross-vein always present, joining the 4th and 5th veins, 

 generally at the discal cell or immediately before it. 



Marginal and submarginal cells varying in number, but normally 

 one marginal cell (which by the presence of the marginal cross- 

 vein may be divided into outer and inner marginal) and two sub- 

 marginal cells, due to the forking of the 2nd longitudinal vein. 

 In rare instances there is only one cell, formed by the coalition of 

 the auxiliary with the 1st longitudinal vein, and the total absence 

 of the 2nd vein. This is quite exceptional and exists only in one 

 Oriental genus, Toxorhina, the cell being known as the marginal. 



Basal cells very elongated, extending practically always beyond 

 middle of wing, thus shortening all the posterior cells. These 

 latter are usually four or five in number, more frequently the 

 former, more rarely six, still more rarely three only.* 



Anal angle of wing of various shapes, in some genera distinctly 

 angled, in others cuneiform, as in some species of Dicranomyia, 

 for which Skuse has proposed the genus Thrypticomyia.-\- 



Life-history. " When the weather is favourable the eggs hatch 

 in little more than a week. The larvae are ash-grey or brownish, 

 more or less transparent, 12-segmented. The head is incompletely 

 differentiated and retractile, and has the maxillae and mandibles 

 more or less horny and stout ; there are short fleshy antennae in 

 most larvae, but they are long and two-jointed in the TIPULIN^. 

 The organs of locomotion generally consist of transverse swellings 

 on the underside of the body, provided with very minute stiff 

 bristles " ( Williston\ 



As a rule the larvae are terrestrial, living in the earth itself or 

 in decomposing wood or leaves, but a certain number are aquatic. 

 A few resemble the caterpillars of Lepidoptera, not only in 

 appearance, but in their colour and mode of life, living on the 

 leaves of growing plants. 



* Anisomera spp., and Dicranomyia whartoni, Needham, a North American 

 species. 



t This genus probably cannot stand, owing to intermediate forms easily 

 and completely bridging the gap between the more cuneiform-shaped wing's 

 and those of normal shape. 



