341 



Verrall*, but differs noticeably in having two hairs instead of six on 

 the dorsum of the thoracic and abdominal segments. It is quite prob- 

 able that pallipcs is not congeneric with the other species, good charac- 

 ters existing in larvae and pupae which may be used for their separa- 

 tion. 



When emerging the imago withdraws the pupal skin either largely 

 or entirely from the puparium. No other genus of Stratiomyiidae 

 known to me does this. The pupa closely resembles that of Xylophag- 

 idae. 



gi:ne;ric characters 



Larva. — Head large, posteriorly retracted within prothorax; an- 

 tennae sessile; maxillae with slender transverse ridges. Thorax and 

 abdomen with a few strong hairs on each segment. Prothoracic 

 spiracles large. Anal spiracles separated, situated in a terminal cham- 

 ber the margins of which protrude lip-like. 



I give a synopsis of the imagines of the North American species 

 of Xylornyia as the only available ready means of identifying them. 

 The key .presented may prove useful to students and save valuable 

 time otherwise required to look up isolated descriptions. 



Key to Species 



1. Hind femora spinose beneath pallipes. 



— Hind femora unarmed 2 



2. Coxae black parens. 



— Coxae in large part yellow 3 



3. Thorax with 2 well-defined yellow vittae on disc americana. 



— Thorax without well-defined vittae 4 



4. Hind femora entirely blaclv aterrima, 5 . 



— Hind femora wholly or largely yellow 5 



5. Pleurae entirely black ; hind femora reddish yellow 



pallidifemur, 9 . 



— Pleurae partly yellow 6 



6. Halteres yellow with a brown spot at base of knobs ; antennae black 



aterrima, $ . 



— Halteres yellow ; antennae reddish on inner side 7 



7. Hind coxae blackened in front ; hind femora reddish yellow ; eyes 



separated by less than one sixth the head-width; furcation of 

 fourth and fifth branches of radius distinctly distad of a line 

 drawn from apex of third branch of that vein to point of furca- 

 tion of first and second branches of media pallidifemur, $ . 



♦British Flies, Vol. 5, p. 36. (1909) 



