1875. 201 



(Muscides), as the liousc-fly and bluo-bottlo, by having the first pos- 

 terior cell of the wingH open at its extremity, the fifth longitudinal or 

 pra-brachial vein running straight or nearly straight to the margin of 

 the wing, while it is curved or bent at an angle towards the fourth or 

 cubital vein in the true Muscides. They may also be distinguished 

 from the more feebly developed or acalypterate families of Muscidce 

 either by the approximation of the eyes of the male, or by the si/e of 

 the alulets, which, though sometimes small, are always very distinct in 

 the Anfhomyiidce, even in those genera in which the eyes are widely 

 separated in both sexes. 



It is of importance to determine which are the most constant, 

 and therefore most valuable points of structure, for the formation of 

 genera. 



The relative size of the scales of the alulets may first be mentioned. 

 In the more typical species they are generally tolerably large, and the 

 lower scale projects considerably beyond the upper ; but in many 

 others they are small, and nearly or quite of the same size, so that one 

 scale completely covers the other. 



In some large groups the arista or style of the antennae is hairy 

 or plumose, in others only tomentose or bare. 



In many species the eyes are hairy, in a still greater number 

 naked. 



In some divisions the abdomen is always spotted, or provided with 

 sub-anal appendages. 



The body and legs are often furnished with various teeth, spines, 

 hairs, and bristles, which are generally constant in form and position, 

 and become very valuable characters for the formation of genera, when 

 they are similarly placed in a number of allied sjjecies. I am indebted 

 to Mr. Verrall for pointing out to me that there are two rows of dorsal 

 bristles always present upon the thorax, in addition to others scattered 

 on the sides, in which the number of sets is always constant in indi- 

 viduals of the same species. There are two (in a few kinds, only one) 

 in front of the transverse suture, by w^hich the thorax is intersected, 

 in a longitudinal line with either three or four strong bristles behind it. 



In addition to the features I have mentioned, the length and di- 

 rection of the veins of the wings is very characteristic of certain groups, 

 as is also the shape of the head and abdomen ; and two genera may be 

 knowm, one by the peculiar shape of the proboscis, and the other of 

 the palpi. 



I will now endeavour to arrange the genera in a tabular or ana- 

 lytical form, and then make a few illustrative remai'ks upon each genus. 



