150 mPTERA OF NORTH AMERICA. [PART IV. 



nota Zett. Dipt. Scand. X, p. 3181 ?) which have the anterior 

 branch of the fourth vein forked. Whether we enlarge the genus, 

 so as to admit these species, or whether we leave it in the accep- 

 tation of the Fauna Austriaca, Trichosticha will contain very 

 heterogeneous elements. The genus Erioptera, in Dr. Schiner's 

 limited acceptation, is a natural group, which I have retained 

 below. It is to be regretted, however, that the author transferred 

 to this group the name of Erioptera, which belongs much more 

 legitimately to his genus Trichosticha, as containing Meigeu's 

 most numerous and typical species.* 



In the Proc. Acad. Nat. Sci. Philad. 1859 (p. 225), I have 

 indicated the principal groups of the North American Eriopterse. 

 They are substantially the same as those which have been more 

 fully defined in the present publication. If I have retained them 

 in the position of groups or subgenera, it is because, in my opinion, 

 the characters which all these species possess in common consti- 

 tute between them a link of afiinity more important than the 

 structural differences which some of them show. Even the- genus 

 Rhypholophus, as defined above, proves by the position of its 

 subcostal cross-vein, the manner in which the second longitudinal 

 vein originates, and, in some species, by the arcuated course of 

 the seventh longitudinal vein, a strong affinity to the genus 

 Erioptera in its present definition. If I have adopted these two 

 genera, it is because the difference in the pubescence of the wings 

 of both affords a ground of subdivision as simple as easily appli- 

 cable to all the species at present known. But it remains to be 

 shown yet, whether the difference in this character is indicative 

 of some corresponding modifications in other organs. Another 

 potent reason for not further subdividing the genus Erioptera in 

 my case was, my unacquaintance with the European species, the 

 rather small number of the North American ones, and the com- 

 paratively large number of subdivisions which they require. For 

 all these reasons I have preferred to indicate the natural affinities 

 existing between the North American Eriopterse, and to distri- 

 bute them in groups accordingly, leaving these groups in the 

 position of subgenera. 



' It may be said in favor of Dr. Schiner's nomenclature, that Meigen, in 

 his earlier work (Klassljicaiion, etc. 1804), has figured Erioptera aUa as 

 if it was the type of the genus. In his principal work the species art} 

 arranged in a different order, and this figure is not reproduced at all. 



