1911] Aldrich — The Dipterous Genus Diostracus 71 



the time of its discovery; at least, there are no references to it 

 in literature, and I have never seen it in any collection examined 

 by me. The discovery of a second species in the Puget sound 

 region enables me to add some chaeto tactic characters, and for 

 convenience I redescribe the genus. 



Generic characters. — Male. Antennae of medium size and simple form, first 

 joint moderately elongated, hairy above, the second short, hairy above and below, 

 the third short with a rounded tip and almost basal arista, which is of medium length 

 and has a very short pubescence. Face wide, short, with a strong transverse suture, 

 the lower part ending in a point in the middle; palpi very large, folded loosely across 

 the front of the large, bulky proboscis, which extends broadly up under the neck. 

 Occiput convex, nearly horizontal above, with a row of orbital bristles extending to 

 the mouth and only sparse beard below; postvertical bristles two, verticals two, aa 

 large as the ocellar. Thorax with absolutely no small hairs on the dorsum except 

 at the extreme front edge; no acrostichals; six strong pairs of dorsocentrals; scu- 

 tellars one pair and several hairs on the edge; humeral one and a few hairs; 

 notopleurals two; posthumeral one; supra-alar two; postsutural one or two small; 

 propleural one rather weak; a row across the first abdominal segment. Pleura 

 bare. Metanotum large, nearly horizontal. Abdomen with six visible segments 

 dorsally besides the hypopygium, which is small but not much embedded; fourth 

 sternite bent out in a V-shape. Hind metatarsus longer than following segment; 

 hind coxa without an erect bristle on the outside. Wings rather long, third and 

 fourth veins nearly parallel, ending in the apex, second vein ending a little before 

 the apex, hind crossvein less than its length from the hind margin. 



Female. Face still wider, palpi not quite so large, more pointed and hairy. Two 

 good-sized postsuturals. 



It will be observed that the added generic characters are not 

 drawn from the type species; but the close correspondence of 

 the new species with the type in all essential known characters 

 of the latter makes it highly probable that the type shows these 

 newly mentioned ones also. The relationships of the genus 

 are evidently with Thinophilus, as stated by Loew; five species 

 of Thinophilus examined by me all agree in having no acrosti- 

 chals, but differ from Diostracus in having the first antennal 

 joint bare and shorter, and in having one notopleural bristle 

 instead of two. In most of their characters, including the large 

 palpi, the two genera are much alike. 



Diostracus olga sp. nov. 



Male. Occiput thickly gray poUinose, showing only a little greenish ground 

 color; postorbitals rather scattering, black, the row extending to the mouth; beard 

 of only a few yellowish hairs; front short and wide, gray poUinose, ocellar tubercle 



