Acroceridae. 159 



very agile and able to make springs in a similar way as the larva 

 of Piophila caset; after hatching tliey then seek an Arachnid and 

 penetrate into it. 



The Acrocends are very curious and characteristic flies on account 

 of their small head, large, bulbous thorax, inflated abdomen and 

 large thoracic squamulæ. They are sluggish and are often sitting on 

 dead and dry branches; they are recorded also sometimes to hower 

 in the air; they are generally rather rare. 



From the palæarctic region 30 species of Acro.cerids are described, 

 and from North Amei-ica 42 species; none are common to both 

 regions. 



No case of parasitic Hymenoptera on Acrocerids is known to me. 



No Acrocerid has previously been recorded from Denmark. 



Table of Genera. 



1. Antennæ inserted on the vertex, above the eye-suture; three 



ocelli 1 . Acrocera. 



— Antennæ inserted near the mouth, below the eye-suture; 



twd ocelli 2. Oncodes. 



Acrocera ^leig. 



Head small. Three ocelli present. Antennæ inserted above the 

 eye-suture, near to the ocelli, they are small and short, two-jointed, 

 with an apical arista. The proboscis is rudimentary or perhaps quite 

 absenl. Thorax is large, bulbous. Abdomen inflated, consisting of 

 iive observable segments. The male genitalia are seen in the apex 

 of abdojnen as a little knob; in the female the last segments, apically 

 to the above mentioned tive, form a little upwardly bent ovipositor, 

 terminating in two lamellæ. The wings show an incomplete venation, 

 which is somewhat different in different species; it seems to consist 

 almost entirely of convex veins. I shall only speak of the species 

 (flobulus; below the costa there is a dark vein which I take to be 

 the mediastinal vein ; then follows a thick vein, I think the united 

 subcosta and radius, it forms a thickened apical part near to the 

 apex ; the next vein is forked and is probably the cubital vein ; in 

 the lower part of the wing lies a vein, forked almost from the base, 

 this is perhaps the postical vein; flnally there is a last vein, nearly 

 reaching the margin; as it is convex it may be the axillary vein. 

 According to this interpretation there are no discai or anal veins, 

 and there is no discai cell. 



The larvæ are parasitic on Arachnids; A. sanguinea Meig. and 

 trigramma Low, were bred from the cocons of Tegenaria agilis (see 



