HOUGH: SOUTH AMERICAN MUSCID.E. 223 



orbit, bucca thinly so, and facial fossa, slaty gray ; the gena 

 and geno-vertical plate, silvery. The small lunula is silvery 

 white. The vibrissa! ridge seems to have a dark yellow ground 

 color, but is so thickly gray poUinose that I can hardly feel 

 certain. The principal vibrissa is on a level, very slightly 

 dorsad the free border of the clj^peus. Ventrad the principal 

 are several secondary vibrissa', and dorsad are a very few small 

 hairs. The gena is naked. The bucca is thickly beset with 

 black, bristly hairs, which are, as usual, larger toward the oc- 

 ciput, and form, along the edge of the mouth opening, a row 

 of tolerably large bristles At the cephalic end of the bucca, 

 along the ventral border of the transverse impression, is a row 

 of about six tiny bristles, which, instead of having the usual 

 direction of the buccal hairs, point caudad and more or less 

 dorsad. A similar row, but of larger bristles, is found in cer- 

 tain species of Hydrotna and Pogonomyia. 



The front of the male is narrow, but not linear, and, more- 

 over, its width is variable in different specimens, being twice 

 as wide in one of my males as in the other. The frontal bristles 

 form a complete series. They are largest at the ventral end of 

 the front, and diminish in size as we pass dorsad, those nearest 

 the ocelli being very small indeed. All are curved cephalad 

 and dorsad, the convexity of the curve being cephalad. Of the 

 bristles at the vertex, the great ocellars are the largest. They 

 are almost parallel, and curve dorsad and cephalad ; convexity 

 of the curve dorsad. The other bristles at the vertex are mere 

 hairs, but one can recognize from their position the inner and 

 outer verticals, the postverticals, the occipito-centrals, and the 

 usual tiny lesser ocellars. The cilia of the posterior orbit, ex- 

 cept the first three or four, are short, but form a well-marked 

 row. On the occiput, parallel to the cilia of the posterior orbit, 

 are other irregular rows. 



The front of the female measures 0.7 mm. in width ; the 

 head is 2.6 mm. wide. The sides of the front are perfectly 

 parallel throughout. The vitta is about four times as wide as 

 one geno-vertical plate, and either black or brown. The geno- 

 vertical plate is silvery poliinose. The transfrontals number 

 about eight, and are of very unequal size. About at the level 

 of the anterior ocellus are two ascending frontals, the more 

 dorsal much the larger. There are no orbital bristles, but lat- 



