TAXONOMY OF MUSCOIDEAX FLIES — TOWNSEND II 



whrch, if still present, would make a taxonomic system simply 

 impossible. 



Taking these points into consideration, there is evidently but one 

 course open. Draw lines of demarcation between the best marked 

 types, and let the others, with their respective coteries of inter- 

 mediate forms, fall in whatever divisions a preponderance of their 

 characters in each case indicates. Definitions of characters for the 

 higher divisions can not be exact, because the forms themselves in 

 nature do not fall into well defined divisions. 



Such a system as outlined would recognize typical forms as genera 

 and species, and would then intercalate necessary additional genera 

 and species for the convenient reception of the intermediate forms, 

 which group around the typical ones and connect them with each 

 other. The one great difficulty here will be to arrive at the true 

 relationships of the intermediate forms, for their affinities are often 

 so complex that it is very hard to decide with what genus or species 

 they are most closely related. The real truth will ultimately be 

 attained only after many years of continued research into their 

 ontogeny, combined with an exhaustive study of the geological his- 

 tory of the superfamily. 



AYhat have been called typical forms, both genera and species, it is 

 proposed to term typic. The additional genera and species to be 

 intercalated between the typical ones it is proposed to term atypic. 

 We will thus have a system of typic genera and atypic genera for the 

 reception of typical genera and intermediates respectively, and typic 

 species and atypic species for the accommodation of the typical spe- 

 cies and intergrades respectively. This scheme accords with the 

 facts, which do not conveniently admit of the employment of sub- 

 genera and subspecies. The latter concepts are here inapplicable 

 on account of the nature and intricate relationships of the forms. 

 To include subgenera, the genera would have to be too loosely char- 

 acterized. Furthermore, this scheme preserves the binomial nomen- 

 clature, which is highly desirable. It can be designated in each case 

 whether a genus is typic or atypic, if this is found desirable. 



All the more primary divisions — those above the subfamilies, up 

 to the very subordinal divisions themselves — can at present be only 

 imperfectly characterized and defined. Here is where aid will be 

 derived from early stage characters, when these become known. 

 Even the Cyclorrhapha and the Orthorrhapha 1 can not be sharply 



1 The writer is aware that Osten-Sacken claims there is a clearer line of 

 separation between the Nemocera and Brachycera than between the Orthor- 

 rhapha and Cyclcrrhapha, but this is outside our subject. 



