J. R. MALLOCH 229 



many very useful characters for the differentiation of closely 

 allied species are used in this paper for the first time. The lack 

 of recognition of these characters by European workers causes 

 a doubt to arise, as to the propriety of arbitrarily deciding whether 

 or not a species should be placed in one or other of the categories 

 in the key, when the character which I use is not mentioned in 

 any availal)le description. 



Descriptive Tennin ology 



In the keys and descriptions in this paper I have utilized the 

 characters and terminology used in my most recent papers on 

 the family. The names designating the various leg surfaces 

 have been adopted from the paper written on the chaetotaxy of 

 Cyclorrhapha by P. H. Grimshaw, which appeared in the En- 

 tomologists' Monthly Magazine in 1901. That paper was con- 

 sidered by the author at the time of its appearance as the first 

 on the subject, but some years afterwards he informed me that 

 he was in error in so considering it, as the method indicated for 

 the leg surfaces at least had been used or suggested by a con- 

 tinental European author some years before. 



In using the system referred to, the legs are assumed to be 

 viewed when at right angles to the body, thus causing the same 

 surfaces of all of them to lie in the same position and to receive 

 the same names. There has been considerable confusion arising 

 fiom the fact that it has not always been possible to determine 

 whether an author meant what I call the ventral, or the posterior 

 surface of the tibia when he referred to the inner side. The 

 inner side may be in the terminology of one writer that side 

 which lies next to the body, while in that of another it may apply 

 to the surface which is opposed to the ventral or under side of 

 the femur. A terminology which is essentially the same for all 

 legs is indispensible for correct descriptions, especially in dealing 

 with species which are as closely allied as arc those in this family, 

 and in all my papers the one now used has been adopted. I do 

 not hold that it is a perfect system, but it is the only one which 

 is thoroughly descriptive and not cumbersome in terminology, 

 a fact which leads me to believe that it will come into more 

 general use as the Muscaridae and Tachinidae find more students. 



TRANS. AM. EXT. SOC, XLVIII. 



