Apropos "Masarygus Brethes 



BY 

 lÍAYMOND ('. RhANNON 



]n a publication, on Syrphidae, 1 placed the ñame Masar ugus as a 

 .subgenerie ñame of Microdon. Doctor Brethes raaintains tliat it slioiüd 

 have generie rank. 



In considering wliether "Masarygus' shonld have generie or snb- 

 generic valué, the following faets shonld be kept in mind. 



1. There is no fixed rnle for defining a genns. In the last 

 analysis it is largely a matter of personal opinión as to what consti- 

 tutes a genns. Aecordingly a genei-ic concept is sul)ject to eliange, 

 and frequently it is based iipon the opinión of the last workev who 

 pnblished on it. Also, it freqnently happens that as more species in 

 a given gronp are stndied, intermediate forms between two so-called 

 genera will be fonnd whieh will definitely elimínate one of them, as the 

 two will then liave to be eombined. (It is easy to find striking diffe- 

 rences between two species from widely separated localities, or even 

 in the extreme types of a genns in the same locality, but when material 

 from intermediate regions, or intermediate forms, are studied it may 

 be found that they cannot be considered separable nnder two generie 

 ñames). As a- striking instance of this very thing, we have recentlj»^ 

 witnessed the placing of thirty-six generie ñames of so-called genera, 

 allied to Anopheles, under the singh' generie ñamo Anophelcs (Christo- 

 phers, Dyav and Root) and of tliis great array of ñames only five 

 have been reserved for nse as subgenerie ñames. This comes as a re- 

 sult of the fact tliat a.t tliis date tlie Anopheline fauna of the entirely 

 world lias been ratlier tlioroughly studied, and the so-called generie 

 differenees have melted away in the process, one by one. 



2, A charaeter, or set of eharacters, which may be considered of 

 generie valué, varies eonsiderably in different groups. In one case a 

 rather insignificant cluiiraeter (at first eonsideration) may be shown 

 to have constant valué in the matter of separating genera in somc 

 groups, but this same charaeter may not have even specific valué in 

 another gronp. Even very striking eharacters which elseM'here would 

 be considered of prime importance in eertain groups are onlj' consi- 

 dered as having specific valué. In other words the definition of ge- 

 nera, should depend largely upon the plasticity of the particular 

 group under eonsideration. 



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