INTRODUCTION 



ROBBER FLIES OF THE WORLD 



11 



44 22 



Text-Figure 3. — The wing of a generalized Recent asilid, Cera- 

 turgus cruciatus Say. Explanation: Costa. 2, Subcosta or 

 auxiliary vein. 3, First branch of the radius, or first longi- 

 tudinal vein (Ri). 4, Second longitudinal vein (R 2 and R3). 

 5, Third longitudinal vein (R4 and R5). 6, Anterior branch of 

 third vein (Ri). 7, Posterior branch of third vein (R5). 8, 

 First branch of medius or fourth vein (Mi). 9, Second branch 

 of fourth vein or anterior intercalary vein (M 2 ). 10, Third 

 branch of fourth vein, or posterior intercalary vein (M3). 11, 

 First branch of cubitus, or fifth vein (CuJ. 12, Second branch 

 of fifth vein (Cu 2 ). 13, Second ana! vein. 14, Main stem of 

 the radius (R). 15, Main stem of the medius (M). 16, Main 

 stem of the cubitus (Cu). 17, First anal vein. 18, Remnant 



of third anal vein. 19, Anterior branch of cubitus. 20, 

 Ambient vein. 21, Radial sector. 22, Humeral crossvein. 

 23, Anterior, small or middle crossvein. 24, Posterior or medial 

 crossvein (m). 25, Discal or mediocubital crossvein. 26, First 

 or basal costal cell. 27, Costal cell. 28, Subcostal or medi- 

 astinal cell. 29, Marginal cell (Ri). 30, First submarginal 

 cell (R 2 and R 3 ). 31, First posterior cell. 32, Discal cell (1st 

 M 2 ). 33, Second submarginal cell. 34, Second posterior cell. 

 35, Third posterior cell. 36, Fourth posterior cell. 37, Fifth 

 posterior cell. 3S, First basal cell. 39, Second basal cell. 

 40, Third basal, anal or lower basal cell. 41, Axillary cell, anal 

 angle (A 2 ). 42, Alula, axillary or posterior lobe. 43, Thy- 

 ridium. 44, Arculus. 



metastemum may be wholly membranous, thinly chitin- 

 ized, or more rarely forming a stout, thick arch of 

 chitin. 



The legs are almost always stout, often swollen and 

 frequently bear numerous, stout bristles. These condi- 

 tions are connected with the active, predatory habits 

 and the need to hold a struggling prey. As Lundbeck 

 (1908) has so well commented, the bristles are of several 

 different categories. They may be stout throughout, 

 or stout basally, becoming fairly attenuate distally ; or 

 in many cases, they are so weak as to render it difficult 

 to decide if they are truly bristles or only bristly, stiff- 

 ened hairs. All tibiae at their apices have several, stout, 

 spinelike bristles. The cluster may contain as many as 

 10 or 12 on the hind tibial apex or as few as 5 or 6 

 bristles. The anterior tibial apex may have a single 

 bristle, which in the course of evolution has thickened 

 into a prominent spine. Its accompanying modifica- 

 tions have been discussed above. The pretarsus ends in 

 pulvilli, sometimes reduced or even absent, and a bristle- 

 like empodium of several forms and variable length, 

 wanting in only one or two Leptogastrinae genera. 

 Claws may be sharp, or blunt, curved or flattened and 

 apically bent; in not pulvillate forms, they become 

 more slender, always finely attenuate and convergent: 



rarely the lateral claw is shortened. 



With few exceptions, the wings have a complete am- 

 bient vein, rarely entirely absent (Nusa Walker) . The 

 radius is 4-branched always, with sometimes a recur- 

 rent spur extending back from the anterior branch of 

 the third vein near the base of this branch. This spur 

 vein is sometimes complete; that is, it unites with the 

 second vein and in Mallophora Macquart and several 

 other genera it simulates a crossvein. It is really 

 equivalent to the posterior branch of the second vein 

 (third branch of radius), which has become lost, and a 

 spur vein, when present, constitutes a vestige of this 

 last vein. The medius has 3 branches, the cubitus has 

 2 branches and the anal cell open or closed and petio- 

 late. In the most generalized condition, the marginal 

 and all posterior and anal cells are open. This condi- 

 tion is seen only in the lower Dasypogoninae and the 

 Leptogastrinae. In many forms, the marginal cell is 

 closed; one and sometimes two posterior cells and the 

 anal cell may be closed or a total of four closed alto- 

 gether. In one instance the submarginal cell is closed. 

 Rarely, the posterior cells may be reduced to four 

 cells; in one instance it is reduced to three cells; the 

 alula is absent in Leptogastrinae and in a few other 

 genera likewise. 



