ART. 28 CHALCID FLIES NORTH OF MEXICO BALDUF 66 



Gager C. Davis. Three females and two males in the entomological 

 collection of the Canadian Department of Agriculture, Ottawa, were 

 collected at Tampico, 111., on June 15, 1909, by G. E. Saunders. One 

 of the pins bears a corky gall, probably of Disholcaspis mamma 

 (Walsh). I have 2 females and 10 males from D. mamma on Q. 

 tnacrocarpa at Urbana, 111., reared in indoor cages from April 20 to 

 June, 1923. L. H. Weld presented three females and one male reared 

 by him at Evanston, 111., from the gall of Plagiotrochus {Callirhytis) 

 tumifica (Osten Sacken) on red oak {Q. Tnaanma). A lone male in 

 the collection of the United States National Museum bears data as 

 follows : April, Riley County, Kans., Marlatt, 983 ; a female (Hopk. 

 U. S. 10777'') reared May 14, 1919, and a male (Hopk. U. S. 10777^) 

 dated May 7, 1919, are both presumably from galls, on Q. minor, at 

 Poplar Bluff, Mo., by S. A. Rohwer. 



It is not possible to distinguish positively between some nigriceps 

 Walsh and certain individuals of glohvXi Balduf. The smaller indi- 

 viduals of the latter grade into the larger specimens of the former, 

 and this merging is also true of the form of the heads, the shape 

 and extent of the band on the wing, and the coloration. I do not 

 place as gldhuli any specimens with an imperfect wing band. This 

 band is very often more or less reduced in nigriceps. The head of 

 the nigriceps as described originally by Walsh is subglobose, and 

 about two-thirds as long as broad, whereas it is always about three- 

 fifths as long as broad in glohuli and approaches a transversely rec- 

 tangulate-ovate form as seen from above. But the lots from the 

 Michigan Agricultural College contain specimens that range from 

 abbreviated bands and somewhat rounded heads in the one extreme 

 to complete bands and rectangulate-ovate heads on the other extreme 

 from the same host. They can therefore be classed as either species, 

 and such a classification is valueless. It is possible that these sup- 

 posed species are all one, but this theory leads to trouble when it is 

 recognized that the larger glohuli grade into the smaller, more 

 stocky-headed forms of duhia Walsh, which certainly is a distinct 

 species by virtue of its size and usually the dimensions of the head. 

 I prefer to believe that three species are involved here, which, how- 

 ever, are not sharply definable in terms of structural characters 

 studied to date. Any arbitrary limitations of size, form, and color 

 are not positively practicable for convenience of separation, and 

 certainly are misleading as means of indicating the true natural 

 border lines of these species, but are now our only known aids for 

 making even approximate distinction. A study of the genitalia 

 may prove helpful in the search for means of separating the border- 

 line specimens. 



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