622 PROCEEDINGS OF THE NATIONAL MUSBUM. vol. xxix. 



medial cross- vein and the origin of R,; by the position of the medio- 

 cubital cross-vein near the posterior end of the radio-medial cross-vein 

 in Manoxyela (fig. 34), its location about halfway between this cross- 

 vein and the point of separation of media in Xychi (fig. 35), its migra- 

 tion toward the base of the wing until still nearer the origin of media 

 in Megaxyela (fig. 31), and Odontophyes (fig. 32), and finally in Macrox- 

 yela (fig. 33), to a position only a very short distance before the origin 

 of media; by the progressive migration of the free part of M^+Cu, 

 from just before the apex of the first anal cell in Xyelaio just beyond 

 the middle in Macroxyela; by the preservation of the radio-medial 

 cross-vein in the hind wings of Megaxyela^ Odontophyes^ and Maci'ox- 

 yela; and by the location of the free part of R^ of the hind wings 

 near the apex of M^ in these same genera. 



It is worthy of note that the Xj^elidte have departed from the type 

 of wing assumed for the original progenitor of the Hymenoptera only 

 in the loss of the free part of the vein Cu.,. It is also of interest that 

 although their wings are distinctly generalized, yet in many ways they 

 have undergone prominent progressive specializations, and that in each 

 case these specializations have not proceeded in the same order. The 

 variation in the order of specialization of the difi'erent genera will be 

 seen in the following lists of genera which are arranged from gener- 

 alized to specialized. If the modifications of the subcosta be taken 

 they would be arranged, thus, Odontophyes^ Megaxyela^ Macroxyela^ 

 Xyela^ Manoxyela; if the shape of the stigma thus, Xyela^ Manoxyela^ 

 Macroxyela, Megaxyela^ Od()ntoj)hyes; if the position of the medio- 

 cubital cross-vein, thus, Manoxyela^ Xyela^ Odontophyes^ 3fegaxyela^ 

 Macroxyela; if the position of the free part of M^+Cui, thus, Xyela^ 

 Odontop>hyes^ Megaxyela^ Manoxyela^ Macroxyela; if the origin of media 

 thus, Xyela, Macroxyela^ Manoxyela, Odontophyes^ Megaxyela. If now 

 the position of the five genera l)e tabulated for the five characters given, 

 it is found that Megaxyela occupies all the positions ))ut the first, and 

 occupies the fourth twice, OdontopJiyes occupies each of the five places, 

 Macroxyela occupies the third and fifth each twice, and does not occupy 

 either the first or foui'th, Manoxyela occupies each of the five places, 

 Xyela occupies the first place three times, and does not occup}" either 

 the third or fifth. 



This family is divisi})le into two subfamilies on the form of the base 

 of the subcosta of the front wings. In one subfamily, of which 

 Macroxyela (fig. 33) may be taken as the type, the subcosta extends 

 from the base of the wing midway lietween costa and K + M to beyond 

 the origin of media, where it divides into two branches, one going to 

 the costal margin, the other extending transversely coalesces with 

 radius. In the other su])family. of which Xyela (fig. 3.5) may be taken 

 as the type, the base of sulx-osta is closely appressed to K + M ))ut 

 does not coalesce with it, to about the middle of the distance between 



