XXXIV 



INTRODUCTION. 



The Wings vary greatly in extent though little in outline, and they do 

 not extend beyond the anus ; sometimes they are rudimentary and in one 

 genus usually entirely wanting. The number of the nervures is not great, 

 and these vary but slightly in extent and position. There are usually three 

 cubital cell?, but the central one, known as the areolet, is extremely 

 variable in shape, and often has its external nervure pellucid or entirely 

 wanting. The wings are nearly, or (juite, transparent or hyaline, covered 

 with extremely minute bristle.s, and none of our species exhibit the violet 

 or black infumescence of the tropical representatives. The point of 

 junction with the thorax is known as the radi.x, which is partly covered by 

 the squamulae or tegulae. 



The above very brief sketch will serve to connect the more detailed 

 descriptions of individual parts contained in the Glossary, and also a 

 few essential characters, which it is necessary to detail at greater length 

 below. 



DETAILS OF THE HEAD. 



A clear knowledge of the various capital characters is of primary im- 

 portance in following the descriptions, which, it is hoped, the accompanying 

 figure will sufficiently illustrate. In it, i is the vertex bearing (2) the 

 ocelli, with the occiput out of sight behind it ; 3 is the frons, the 

 lower part of which is excavate, glabrous, and forms the antennal scrobes 



(4), and the insertion of the antennae (5) ; 

 6 is the face, the central portion of which is 

 often convex and termed the epistoma ; 7 is 

 the clypeus, with the lateral foveae circularly 

 indicated before (8) the cheeks ; 9 is the 

 labrum, in front of which are (10) the bifid 

 mandibles ; 1 1 is the ligula or tongue; 12 

 one of the two maxillary palpi, and 13 a pro- 

 portionate labial palpus ; 14 are the compound, 

 reniform eyes, with (15 to 15) their orbits, 

 which also extend throughout their posterior 

 circumference. The basal side of the head, 

 i.e., that nearest the prothorax, is attached to 

 the latter by a very slender peduncle. Some 

 distance above this peduncle is a raised mar- 

 gin, which forms the lower edge of the occiput 

 and extends on either side of the head to the lower extremity of the 

 cheeks, known in its lower part as the genal costa. This costa is some- 

 times nearly or quite straight, from level with the peduncle downwards, 

 but at others is inflexed or obtusely angulated some distance from its apex. 

 Viewed from above, the head varies greatly in length and breadth behind 

 the eyes, being of' en very short and narrow, occasionally as long as the 

 eyes themselves appear from that position ; and, when inflated in such a 

 way as to be laterally broader than the eyes, it is said to be buccate. 

 The cheeks in the figure are normal. When so broad and vertically 

 straight as to form a right angle with the clypeus they are termed buccate ; 

 occasionally they are so narrow that the head is triangular, viewed from 

 in front. A genal sulcus is sometimes present upon the disc of either 

 cheek, extending from the lower extremity of the eyes to the base of the 

 mandibles. 



Details of the Head.— i, vertex ; 

 2, ocelli ; 3, frons ; 4, antennal 

 scrobes ; 5, insertion of anten- 

 nae ; 6, face ; 7, clypeus ; 8, 

 cheeks ; 9, labrum ; 10, mandi- 

 bles ; II, ligula ; 12, maxillary 

 palpus ; 13, labial palpus ; 14, 

 eyes ; 15, orbits. 



