ANNALS OF NATURAL HISTORY. 



XXIV. — Remarks on the Generic Distribution of the British 

 Hydromyzidae (Diptera). By A. H. Haliday. 



1 HE multitude of genera and species contained in the family 

 MuscidcB makes it convenient to employ some intermediate 

 divisions between the family and the genera. At the same 

 time their affinities are so multiplied and intricate that few of 

 the divisions which have been proposed can be considered as 

 generally recognised. This is more particularly the case 

 with the subdivisions of the third grand section AcalyptercB. 

 Meigen has omitted all such intermediate steps, but the order 

 of succession in which his genera are disposed supplies in 

 part the deficiency. Fallen, R. Desvoidy, Macquart and La- 

 treille have each proposed a general arrangement, but their 

 methods vary considerably, and especially in this section of 

 the family. Of the groups instituted, Fallen's tribe of Hy- 

 dromyzidce may be considered as one of the most established, 

 being adopted by Latreille with very little alteration. None 

 of this tribe, except the singularly formed Musca Mantis of 

 DeGeer, had been described before the appearance of Fallen's 

 Essay in the Stockholm Transactions for the year 18 13, in which 

 the tribe first assumed a distinct character and definite limits. 

 The author has here described nineteen genuine species, and 

 characterized most of the genera ultimately admitted. The 

 Dolichopidce were included with this tribe in the first sketch 

 of his arrangement of Diptera, published three years before. 

 How great an advance was made in the interval is evident. 

 Latreille adds to the tribe the exotic genus Ropalomera, and 

 excludes from it the type of Fallen's genus Hydromyza, Musca 

 livens of Fabricius, referred to the Cordylurae in accordance 

 with Meigen's arrangement. There seems no reason to doubt 

 that such is the true affinity of this insect, and it is only un- 

 fortunate that the typical generic name was appropriated by 

 Fallen to the only extraneous species which he has admitted. 

 Ann. Nat. Hist. Vol.3. No. 17- June 1839. r 



