832 



AN INTRODUCTION TO ENTOMOLOGY 



transform. The pupae of the Stratiomyiidae are enclosed within the last 

 larval skin, differing in this respect from other Brachycera (Fig. 1064). 

 This is a large family ; more than three hundred species, represent- 

 ing more than forty genera, have been described from North America 



Family XYLOMYIID^ 

 I group together here, provisionally, two genera, as representing 



/?> S( 



Fig. 1065. — Wing of Xylomyia. (After Verrall.) 



a separate family, that have been placed by some writers 

 in the Stratiomyiidae and by others in the Rhagionidas. 

 These genera are Xylomyia and RhacMcerus. Both differ 

 from the Rhagionidae, as restricted here, in the form of 

 the antennas, they clearly belong with the Anomalous 

 Brachycera. They differ from the Stratiomyiidae in that 

 the branches of radius are not crowded together near the 

 costal border of the wing and in the possession of tibial 

 spurs. They agree with each other and differ from all 

 other Anomalous Brachycera found in our fauna in that 

 cell M3 is closed (Fig. 1065). 



Xylomia. — This genus includes rather elongate flies, 

 somewhat Ichnenmon-like in appearance, which are mainly 

 of black coloration with more or less yellow markings. 

 The fiagellum of the antennae consists of eight closely con- 

 solidated segments, the last of which usually bears a tiny 

 style (Fig. 1066). Six species have been described from 



our fauna. 



Fig. 1066.-- 



Antenna 

 of Xylo- 

 m y i a . 

 (After 

 Verrall.) 



The larvae of Xylo- 

 myia pdllipes have been 

 found under the bark of 

 fallen trees and are pre- 

 dacious. 



RhacMcerus. — The members of 

 this genus resemble Xylomyia in the 

 form of the body but differ mark- 

 edly in the structure of the antennae. 

 In Rhachicerus the fiagellum of the 

 antennae consists of from twenty to thirty-five segments. The seg- 

 ments of the fiagellum are more or less cup-shaped ; and in some species 



Fig. 1067. — Antenna of Rhachicerus 

 (From Williston.) 



