86 



[Miirch, 



legs are also provided with numerous spines, which are ari-anged in 

 different manners. The wings have the first posterior cell more or 

 less closely contracted and sometimes closed at the end, where it joins 

 the costa, by the apical cross vein, which is formed by the bending 

 upwards of the fourth longitudinal vein. 



It is chiefly by variation in the above characters that the genera 

 and species are distinguished from each other ; and the formation of 

 genera has been found so difficult, owing to the impossibility of de- 

 ciding between generic and specific chai'acters, that some authors have 

 given up generic division of the Family altogether. This, however, 

 has been found so incouvenieut, that some artificial arrangement, with 

 .the adoption of generic names, is absolutely necessary. I have, 

 therefore, drawn up an analytical table of genera, taking the charac- 

 ters from Macquart, Schiner, Rondani, and others, which I will insert 

 before commencing the diagnosis of species. 



TABLE OF GENEEA. 



First posterior wing cell open at the end.* 



Arista with the second joint elongated. 



Arista straight; the second joint much shorter than the third. 



Antennae with the second joint elongated. 



Antennse with tlie second joint longer than the third 



1. EciiiNO.MTiA, Dumcr. 



Antennae with the second joint shorter than the third. 



Palpi rudimentary 2. Micropalptjs, Mcq. 



Palpi normal. 



Proboscis very long, straight, and slender 3. Aphria, Dsv. 



Proboscis rather long, but thick; fronto-orbital bristles in a double row 



in both sexes 4. Demoticus, Mcq. 



Antennae with the second joint short. 



Arista geniculated ; the second joint nearly or quite as long as the third. 



Head wide and swollen. 



Cheeks tumid, facial angle nearly straight 5. Gonia, Mgn. 



Clieeks not tumid, facial angle inclined backwards... 6. Gebmaria, Dsv. 

 ITcad neither wide nor swollen. 



Proboscis long, slender, and twice elbowed 7. Sipiiona, Mgn. 



Proboscis of the ordinary shape. 



Wing-veins setigerous. 



Fourtli longitudinal vein bent in a curve to form the apical cross vein ; 



abdominal segments without discal setae 8. Thbtptocera, Mcq. 



Fourtli longitudinal vein bent at an angle ; abdominal segments with 



discal setae 9. Bigonicheta, Rnd. 



In some genera the aperture in certain species is very small, or eren quite closed. 



