392 DIPTEKA. 



found the pupae enclosed in smooth oval cells ; they are naked, 

 the thorax gibbous, with the rudimental wings and legs very 

 short. Bibio albipennis Say, a white-winged species, is double- 

 brooded, and flies in swarms in June and October, alighting 

 slowly on the passer-by. 



RHYPHID^E Loew. This family is known by the wings hav- 

 ing a perfect discal cell, while the empodium resembles a 

 pulvillus ; the pulvilli being wanting. The single genus 

 Rhyphus has short fourteen-jointed antennae, the second joint 

 of the palpi swollen, and the legs are not spiny. Rhyphus 

 alternatus Say, is common on windows. 



The succeeding families belong to the Brachycera, or short- 

 horned flies. 



XYLOPHAGID^E (Macquart). This family is known by the 

 three basal cells of the wings being very prolonged, the an- 

 nulated third joint of the antennae always without a style or 

 terminal bristle, and by the spurred tibiae. Xylophagus has 

 ten-jointed antennae, with the ovipositor very long. The larva 

 is cylindrical, with an oblique scaly plate on the tail, while the 

 head ends in an acute horny point. Loew doubtfully refers 

 the genus Bolbomyia, found fossil in the Prussian Amber, to 

 this group. 



STRATIOMYID.E Latreille. The wings in this group have the 

 three basal cells much prolonged, and the costal vein reaching 

 only to the middle of the wing. The third joint of the an- 

 tennae is sometimes subdivided into several portion?. The 

 tibia- are spnrless and the pulvilliform empodium is much 

 developed. The eoarctate pupa retains the larva skin nearly 

 in its original form. The genus Beris is easily distinguished 

 by having seven, instead of five (the usual number) abdominal 

 segments visible. In *sw/v///,s- the eves of the males approxi- 

 mate much closer thai: in the females. They are showy insects, 

 with bright metallic colors, and are widely distributed over the 

 earth. The larva live- in the earth, is oval oblong, narrowing 

 before; the head is scaly, with two ocelli, and armed with two 

 hooks, while the body is hairy. Fig. 313 represents a pupa 



