Dec, 1918] Nearctic Species of the Genus Laphria 147 



This latter character exists in varying degree and probably 

 there is a complete intergradation between the genera in this 

 respect. In some specimens of Lampria rubriventris, the 

 tubercles are evanescent. However, the genus Laphria is so 

 large (more than 300 described species) that it is not desirable 

 to merge with it separable groups even if absolutely trenchant 

 characters are not available. 



The same argument applies in the case of the species grouped 

 under Dasyllis. Professor M. Bezzi has pointed out* the lack 

 of definitely separating characters between Dasyllis and Laphria, 

 but it must be admitted that Dasyllis has a typical general 

 appearance different from most species of Laphria, and that 

 the male genitalia are of a different type (see Figs. 24 and 25) . 

 According to the opinion of Col. J. E. Yerbury, cited by Dr. 

 S. W. Williston,t there is but one species of Dasyllis, the type 

 species, Laphria haemorrhoa Wiedemann. Not having seen 

 this species, I am unable to comment on the case. 



Niisa should be regarded as a genus distinct from Laphria, 

 not on the usually cited character of decided narrowing or 

 closure of the first posterior cell, which is illusory, but on the 

 grounds of a distinct type of genitalia (in which body of the 

 forceps is simple, but one or both sets of claspers are exposed, 

 taking the position of the apex of the forceps in Laphria, (see 

 Fig. 26), and upon habitus, an important feature of which is 

 the full set of thoracic markings, including three pairs of lateral 

 lunules. Many of the species have also swollen femora and 

 curved tibiae. 



Key to the Males of Nearctic Species of Laphria Based Chiefly on Char.'VCTERS 



OF the Genitalia. 



a. Forceps comparatively slender, nearly straight when viewed from above (except 



in aktis, Fig. 3), with a falcate process forming part of outer lateral surface. 



b. Forceps somewhat spatulate, and nearly straight when viewed from above. 



c. Falcate process rather broad and blunt (Fig. 4); pale (golden) pubescence 



most conspicuous on posterior half of thoracic dorsum. . . .janus n. sp. 



cc. Falcate process more slender and acute. 



d. Forceps, viewed from side, decurved at tip (Fig. 1); general pubescence 



reddish tawny vulhir OS. 



dd. Forceps not decurved at tip (Fig. 2); general pubescence golden. . . . 



sericea Say 



bb. Forceps not spatulate, curved when viewed from above; falcate process very 

 slender and acute (Figs. 3, 3a); general pubescence golden — aktis n. sp. 



* Zeitschr. f. syst. Hym. u. Dipt. VII, 2, March 1, 1908, pp. 108-110. 

 t Manual of North American Diptera. Third Ed. 1908, p. 389. 



