276 Oithorrhapha brachycera. 



present in all. Scutellum with two to foiir marginal bristles, or (in- 

 cana) without bristles. Metapleura without hairs. Abdomen some- 

 wbat flattened, consisting of eight distinctly visible segments. Tbe 

 male genitalia are large or somewhat large, they consist of a large, 

 arched plate belovv, and some complicated, more or less hook-shaped 

 pieces above, forming a forceps. In tbe female tbe abdomen is 

 pointed and terminates witb two styliform lamellæ. In all species 

 tbe abdomen bas a fme pruinosity, which is arranged in siich a way, 

 tbat wben abdomen is viewed in a certain direction one balf of it 

 looks grey tbe other blackisb or at all events a difference in tbe 

 colom* is seen, tbe dividing Hne lying along tbe middle; wben ab- 

 domen is tben viewed in anotber direction tbe difference in tbe bue 

 cbanges to tbe reverse. Tbe legs are somewbat robust, not long; 

 front coxæ only very sligbtly elongated; front femora more or less, 

 but generally not mucb tbickened. Tbe legs are mainly short-baired 

 or a little longisb baired, and more or less beset witb bristles; tbe 

 tibiæ generally witb subapical or apical bristles or spurs. Tbere are 

 two claws, two ratber large pulvilli and a small, linear empodium 

 with bristles below. Wings witb tbe mediastinal vein not reacbing 

 tbe margin; tbe cubital vein unforked and tbus one cubital cell; tbe 

 discai vein likewise unforked, tbus tbree posterior cells; no discai 

 cell; tbe low^er brancb of tbe postical vein and tbe anal vein absent, 

 tbus no anal cell; tbe two basal cells of equal lengtb. No stigma. 

 In one species (arenaria) tbe wings are small, but witb a normal 

 venation. Tbe axillary lobe somewbat developed, tbe axillary angle 

 sballow, Alula not developed, tbe margin bere fringed. Alar squamula 

 very small, with long hairs at tbe margin. 



Tbe developmental stages of Chersodromia are not known. 



Tbese small flies are very characteristic among the Empids; w^ben 

 running on tbe sand they are at first sight often not recognised as 

 Empids, as their exterior may to some degree recall tbat of small 

 Muscids or Borborids. They occur on sandy sea-sbores, some species 

 (e. g. cursitans) may also occur at streams and lakes. Tbe Danish 

 species have bitberto been taken only in a few localities, but they are 

 probably mucb more widely distributed at our shores. In one locality 

 I took cursitans, difficilis, arenaria and incana together, but it was 

 interesting to see, tbat tbere seemed to be some difference with regard 

 to the exact piaces, on which they occurred; cursitans and difficilis 

 were especially running on tbe wet sand and quite down to the 

 water; the bright grey incana on the other band w^as seen a little 

 longer inwards, where the sand was dry and hence of white colour; 

 arenaria was especially running betw^een stones and in the sea-weed 



