480 TROMOPTERA 



tance with the lower branch of the discal vein, and thereby appearing 

 to be a third veinlet from the discal cell), 

 g- Lower branch of the po.stical fork. 

 h Anal {or 6tk IryagitwUnal) vein. 

 / Axillary vein. 

 Ji Pnefurca = the common stem of the radial and cubital veins. 



Ambient vein = the continuation of the costal vein round the hindmargin of the 

 wing. 



Cross {or transverse) veins. 

 w Humeral ciross-vein. 

 X Discal {or middle) cross-vein. 



y Lower {or small) cross-vein, ahvays absent in the Bomhylidce. 

 z Anal cross-vein = r/"'^, when that vein unites with the anal vein before the wing- 

 margin. 



Cells. 



1 Costal {or mediastinal) cell. 



2 Subcostal cell, sometimes almost lost in Bomhylidce through the close approxi- 



mation of mediastinal and subcostal veins. 



3 Marginal cell. 



4 Submarginal cell. 



4'' (Second submarginal {or cubital) cell {or cidntal fork-cell), which when 

 4 is divided by an adventitious cross-vein as in fig. 278 becomes the 

 third submarginal cell and so on. 



5 First posterior {or suhapical) cell. 



6 Discal cell. 



6=* Second posterior cell. 

 6'' Third jjosterior cell. 



7 Postical {or 4th j^osterior) cell = the 5th posterior cell of the Tahanidce, Therevidce, 



Asilidcf, etc. 



8 Axillary cell. 



9*' Upper {or 1st) basal cell. 

 9'' Second {or middle) basal cell. 

 9" Anal {or 3rd hasal) cell. 

 10 Alula. 



Notes on the Venation of the Bombylid.e. 



The peculiar characteristics of the venation of this family lie in (1) the presence 

 of only Four or Three Posterior Cells, and (2) the complete Absence 

 of the Small Cross-vein. 



(1) The Discal Cell emits (irrespective of the ui:»per branch of the postical vein) 

 only two (or sometimes only one) veinlets towards the wingmargin, of which the upper 

 often bends up to (and sometimes even joins) the lower branch of the cubital fork 

 some distance before the wingmargin, and then closes the first i3osterior cell. There 

 are therefore never more than four nor less than three posterior cells, and this 

 character gives an infallible distinction from the 7Vierevid(e, Asilidct^, Tahanidce, etc. 

 The cubital fork is liable to throw a veinlet from its upper branch to near the 

 end of the radial vein and thereby cause the existence of three submarginal cells, 

 while sometimes other cross-veinlets occur in connection Avith the cubital fork and 

 cause a fourth or even a fifth submarginal cell, l)Ut these extra submarginal cells 

 are very unlike the tiiird submarginal cell which occurs in many Asilidce. as in the 

 latter the veinlet is recurrent to almost the base of the radial vein. 



(2) The Small Cross-vein is entirely absent, as the upper branch of the postical 

 fork forms for a long (or rarely punctiform) distance the lower margin of the discal 

 cell. It is, of course, possible for an inexperienced student of venation to mistake 

 the base of the upper branch of the postical fork for a small cross-vein, but when it 

 is recognised that the ])Ostical vein always has a large open fork in all the families of 

 the Brachycera until after the AsiUda- no such misinterpretation should be 

 possible. This character also distinguishes the family from the Therevidve, 

 Tahanidce, etc. 



Other details worthy of note lie in the frequent close approximation of the 

 mediastinal vein to the subcostal, thereby making the latter for once in a way 



