ART. 28 CHALCID FLEES NORTH OF MEXICO BALDUF 7 



equal or siibequal, and proportionately longer than those of female; 

 petiole almost three times as long as broad, abdomen subcylindrical, 

 posterior segments six in number when fully extended, but apical 

 ones usually not visible, telescoped, first two combined shorter than 

 third, fourth shorter than third, and remaining three tapering to 

 pointed posterior when exposed, penis often partly exserted on 

 pinned specimens. 



SpeGiflc characters.— li has been very difficult i<y find constant 

 t'haracters for the separation of species of Decatonm. Color and 

 sculpture are subject to such individual variation that they can be 

 used only in a restricted way. Some of the variation in color de- 

 pends on the age at which a specimen is killed, fully matured speci- 

 mens being generally darker. Other variations may be due to the 

 different rates of fading; the submarginal band of the wing, for 

 example, seems to fade more rapidly than the body colors. The 

 form and extent of the sul^marginal band vary greatly in certain 

 species, while in others they are nearly constant. 



Extensive study of the body sculpture has demonstrated very wide 

 variations in nearly all species; and the time and effort necessary to 

 determine the limits of specific variation in sculpture have not 

 seemed justified. 



The vestiture of the body, legs, and wings offers very little of value 

 in the way of specific characters. The general surface vestiture of 

 the wings is for the most part very constant in density and length, 

 though in one species, D. -fiamimnneiventris Girault, it is distinctly 

 shorter than normal. The best characters of vestiture are found in 

 the number of setae on the submarginal vein, which varies somewhat 

 with the size of the individual and apparently within certain limits 

 for each species. 



The dimensions of the various parts of the body offer some spe- 

 cific differences, though the telescoping of the abdomen and the 

 collapsing of the antennal club must be taken into account in the 

 evaluation of characters drawn from those parts. Some of the most 

 available characters of this sort, though these are not without varia- 

 tion, are found in the dimensions of certain joints of the funicle and 

 in the relative length and breadth of the head, and the contour of the 

 eyes, face, and vertex. Certain of these characters are useful in 

 grouping related species. 



The characters that seem to be most useful have been employed in 

 the following key: 



KKY TO SPEXMKS OF DECATOMA 



1. Front wing immaculate (pi. 2, tigs. 23-26) 25. 



Front wiug with a more or less distinct color band extending 

 backward over surface from stigma (pi. 1, tigs. 1-13; pi. 2. 

 figs. 14-22) ^- 



