MYODARIA 



77 



That the group is a difficult one, even for the expert, 

 is only too true. Full descriptions and figures are al- 

 most indispensable in many, if not most cases for allay- 

 ing doubt as to genera, especially in the present chaotic 

 condition of the nomenclature of the Calypterae. I have 

 used the more commonly employed distinctions for the 

 'families' of the Calypterae, and there can be no question 

 but that these, oftentimes trivial, characters do, for the 

 most part, define natural groups, but not in all cases, 

 and the student must find for himself the divergent, 

 anomalous, or homoplastic forms. And, as a general 

 rule in taxonomy, he should remember that differences 

 are of more importance than resemblances in defining 

 relations. That we shall discover more natural charac- 

 ters for their definition soon is without doubt, but, until 

 specialists come to some fairly general agreement as to 

 what these characters are, we must continue to use those 

 which bring together the great majority of the forms into 

 genetic groups. 



Czerny and Hendel place much importance on the di- 

 rection of the postvertical bristles in the arrangement of 

 the Acalypterae, and I am disposed to admit the justice 

 of their claim in large measure. According to these 

 authors these bristles are convergent in the Helomyzidae, 

 Sapromyzidae, Drosophilidae, Geomyzidae, Milichinae 

 and Ochthiphilinae; erect in the Trypetidae; divergent 

 in the Cordyluridae, Heteroneuridae, Ortalididae, Micro- 

 pezidae, Sciomyzidae, Sepsidae and Lonchaeidae, as these 

 authors accept these families. 



Upon the cruciate bristles of the front they also place 

 not a little weight, as present more or less in the Antho- 

 myidse, Heteroneuridae, Ephydridae, etc. It must be 

 remembered, however, that all these bristles are usually 

 minute, often exceedingly so; or absent in forms closely 

 related otherwise to those having them well developed ; 



