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and the presence of breaks in the costa. Sc may be complete (extending to costa) or incomplete (not extending to costa, fading out distally or fusing with Ri). Costal breaks are points on the costa where the sclerotization is weak or the vein appears to be broken; they are best seen with transmitted light.

The muscoid flies are divided into 2 groups, the acalyptrates (Section Acalyptratae) and calyptrates (Section Calyptratae, p. 302), chiefly on the basis of the development of the calypters and the structure of the 2nd antennal segment.

Acalyptrate Muscoids: Section Acalyptratae

Calypters absent or vestigial. Second antennal segment without a longitudinal suture (except in some Psilidae); see p. 283.

This Section includes a large number of families, many of which are difficult to separate. The key below should be of value in separating these families. See illustrations on pp. 283 and 287 for technical characters.

1. Coxae widely separated; wingless ectoparasites of the

Honey Bee Braulidae (p. 295)

1'. Coxae close together; not ectoparasitic in habit; wings nearly alway present 2

2'. Sc incomplete 17

3(2). Posterior spiracle of thorax with at least 1 bristle; palps vestigial; head spherical; abdomen elongate and usually narrowed at base Sepsidae (p. 290)

3'. Without this combination of characters 4

4(3')• Dorsum of thorax flattened; legs and abdomen very bristly; seashore species Coelopidae (p. 290)

4'. Without this combination of characters 5

5(4'). Oral vibrissae present 6

5'. Oral vibrissae lacking 8

6(5). 2nd basal and discal cells confluent

Aulacigastridae (p. 294); Curtonotidae (p. 302) 6'. 2nd basal and discal cells separated 7

7(6'). Costa broken only near humeral cross vein; eyes with microscopic pubescence Acartophthalmidae (p. 294)

7'. Without this combination of characters

Piophilidae, N eottiophilidae (p. 292);

Thyreophoridae, Lonchaeidae (p. 294); Clusiidae (p. 295);

Trixoscelididae, Heleomyzidae, Chyromyidae (p. 296) 8(5'). Costa broken near humeral cross vein

Acartophthalmidae (p. 294) 8'. Costa entire, broken near end of Ri, or broken near humeral cross vein and near end of Ri 9

9(8'). Rs cell narrowed, distally; legs long and slender

Micropezidae, Tanypezidae, Neriidae (p. 286) 9'. R5 cell not narrowed distally, or legs not particularly long and slender 10

10(9'). Eyes prominently bulging, vertex sunken; femora enlarged Ropalomeridae, Rhinotoridae (p. 286) 10'. Without this combination of characters 11 11(10'). Tibiae with preapical bristles 12 11'. Tibiae without preapical bristles 13 12(11). Postvertical bristles converging; 2A short, not reaching wing margin Lauxaniidae (p. 292)

12'. Postvertical bristles parallel, diverging, or absent; 2A reaching wing margin, at least as a fold Sciomyzidae, Dryomyzidae (p. 290); Heleomyzidae (p. 291) 13(11'). Ocelli absent; medium-sized to large flies, wings usually patterned Pyrgotidae (p. 288)

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