309 



apical pvoeesscs; or upon i)eiiultimate or antepenultimate seg- 

 ment ; body not shagreened or visibly striated 3 



2. Head not retractile; body flattened, surface finely shagreeiied, 



sometimes with lateral abdominal spiracles, without vestigial 

 pseudopods ; spiracular fissure transverse, sometimes rather small ; 

 pupae enclosed in larval skin Stratiomyddae (p. 315). 



— Head retractile; body cylindrical, surface not shagrcened, usually 



longitudinally striated, abdomen with a girdle of pseudopods on 



each segment ; spiracular fissure vertical ; pupa free 



Tabanidae (p. 355) . 



3. Posterior spiracles situated upon apical segment .4 



— Posterior spiracles situated upon penultimate or antepenultimate 



segment . 



10 



4. Projecting portion of head and flattened apical plate of terminal ab- 



dominal segment heavily chitinized: the former cone-shaped, en- 

 tirely closed except at extreme apex, not retractile; the latter 

 obliquely truncate and with projecting processes 5 



— Projecting portion of head more or less retractile, not cone-shaped, 



the movable portions not enclosed; apical abdominal segment 

 without a heavily chitinized flattened terminal plate 6 



5. Head about twice as long as its greatest width; thoracic segments 



not chitinized above, each with 2 internal separated chitinized 

 plates ; body without long hairs ; apical plate very large, spiracles 

 vertically elongated, apical paired protuberances small, widely 

 separated, each with a short hair on inner side ^- • • 



COENOMYIIDAE (p. 351) . 



— Head at least 3 times as long as its greatest width ; at least the first 



and second thoracic segments chitinized above, no internal chitin- 

 ized plates present; body with a number of long hairs, 4 of which, 

 in a vertical series on each abdominal segment, are very notice- 

 able; apical plate rather small, spiracles rounded, apical paired 

 protuberances large, fused basally, each with a number of rather 

 long hairs Xylophagidae (p. 346) . 



6. Posterior spiracles widely separated, located in an apical transverse 



cleft; head very small,' retractile Nemestrinidae (p. 368). 



— Spiracles not located in an apical transverse cleft 7 



7. Apical alxlominal segment ending in 2 long processes which are 



fringed with long soft hairs; abdomen with paired pseudopods 

 and fleshy dorsal and lateral appendages. .Leptidae, pt. (p. 362). 



— Apical abdominal segment not as above, paired abdominal pseudo- 



pods usually, other appendages always, absent 8 



8. Apical abdominal segment ending in 4 short pointed processes or 2 



fleshy lips ; internal portion of head with a large, arched, chitin- 

 ized upper plate, the longitudinal rods and other cephalic parts 

 on a horizontal plane Leptidae, pt. (p. 362). 



