0|C> I March, 



upon the dorsuin of tlie thorax, some species having four, many only 

 three, and a few only two, behind the transverse suture (see figs. 

 1, 2, 3). 



Besides these important characters, there are some others of 

 secondary value, which are often useful for the determination of nearly 

 allied species ; for instance, the presence or absence of the costal 

 spine upon the wings, the width of the frontal space between the eyes, 

 the size of the bristles upon the cheeks, &c. 



To facilitate the description of the species, T shall first arrange 

 them in an analytical manner, and in so doing, shall closely follow the 

 method adopted by Eondani in the 5th vol. of his " Prodromus Diptero- 

 logiae Italicae," a work from which I have derived much valuable in- 

 formation respecting this genus. 



ANALYTICAL ARRANGEMENT. 



A. Apex of aljilomen black or grey in both sexes. 



B. Wings without spines upon the second longitudinal veins. 



C. Posterior tibia; of i bearded ou their inner sides. 



D. Abdomen with two spines in the centre of the edge of the second segment. 



E. Thorax with four bristles behind the transverse suture in the two dorsal rows. 



1. Caknaeia, Lin. 

 EE. Thorax with only three dorsal bristles behind the suture. 

 a. First anal segment shining black in <J . 



2. Albiceps, Meig.* 

 3. Atkopos, Meig. 



4 SiiiiLis, sjj. 71. 



aa. First anal segment grey in 6 . 



DD. Second abdominal segment without central dorsal spines. 



F. Thorax with four dorsal bristles behind the suture. 



FP. Thorax with three dorsal bristles behind the suture. 



6. First anal segment of <J extruded and shining black. 



5. Melasuka, Meig. 



Ih. First anal segment of <J mostly retracted, and, when exposed, grey, not black. 



C. Ar.KicoLA, Meig. 

 CC. Posterior tibia; of <J without beards on their inner sides.f 



G. Abdomen with two central spines upon the edge of the second segment. 

 H. Arista with short hairs. 



a. Arista almost bare. Third joint of antenna; thickened. 



7. Laticoknis, Meig. 



aa. Arista with short, but distinct, hairs at the base. Third joint of antenii;e of the 



ordinary shape. 



8. NiGEiTENTKia, Meig. 



HH. Arista with long hairs. 



b. Posterior tibia; of S with a few long hairs upon their inner sides. 



c. Surface of abdomen tessellated in the ordinary manner. 



9. JuvENis, Rond. 

 CC. Abdomen marked with three longitudinal black lines. 



10. Clathrata, Meig. 



♦ In this and the following species, {^s well as in many others, it is exceedingly difficult to 

 determine the ? unless it is captured along with the <J , as the distinctive characters are peculiar 

 to the latter sox.— R. H. M. • 



+ In soino .-species there are a few scattered haii-s. — R. H. M. 



