Description of a New Dipterous Insect. By J. Deby. 185 



lower margin, the breadth of which fringe is equal to the diameter 

 of the wing. The halteres are distinct and spatulate. No traces of 

 nervures are discernible on the surface of the wings. 



The total length of the wings in the males is l* 20-1 •26 mm., 

 in the female • 51 mm. only. The maximum width is only * 15 mm. 

 The halteres measure in the male 0'12 mm. in length. These 

 abortive wings seem to be useless to the insects. 



Abdomen. — The tergites in both sexes number eight. A few 

 scattered bristles occupy the dorsum of each of them and a trans- 

 verse trachea, seen by transparency, runs near and parallel to their 

 anterior border, curving down along each side. This is best seen by 

 means of the paraboloid. The tergites of the male measure in length 

 • 36 mm. each ; equal to 2 • 88 mm. for the whole length of the 

 abdomen ; those of the female measure ° 45 mm ■. each in length ; 

 equal to 3 • 60 mm. for the whole length of the abdomen. The 

 maximum breadth of the tergites is 0*57 mm. in the male and 

 • 75 mm. in the pregnant female. 



Abdominal Appendages. — $. Each branch of the powerful 

 anal forceps of the male is bi-articulate ; the basal joint being 

 massive and carrying long scattered bristles. The terminal joint is 

 less than half as long and half as broad as the preceding one which 

 supports it. The apex of this small joint is provided with a number 

 of short, hard, acute teeth intermixed with which are some fine 

 bristles. The apical joints articulate into the basal joints, so as to 

 permit their folding back between these last, when not in use, so 

 that their points are turned inwards. 



The ovipositor in the female is formed of two plates or valves 

 which cover two internal styles. These protecting plates, viewed 

 laterally, are somewhat lunate and rounded below, obliquely truncate 

 at the apices and clothed with a very short or obsolete pubescence. 

 The inclosed stylets are delicate, membraneous, and end very acutely 

 at some short distance from the tip of the outer sheaths of the 

 ovipositor. The length of the ovipositor is • 33 mm. 



The total length of the imago averages for the males 3 ■ 99 mm. ; 

 for the females, 4-50 mm. 



The colour of the males is dark cinereous, nearly black, the feet 

 and antennsB being somewhat lighter ; the females have a lurid hue, 

 the abdomen when distended with eggs having a dirty yellowish or 

 greenish tinge. 



The Larva. — The larva of Psamathiomya is linear, vermiform, 

 and of a yellow colour. 



The apparent number of segments of the body, including the head, 

 is twelve, one for the head, three for the thorax, and eight for the 

 abdomen. 



The thoracic segments are shorter than the following ; the apical 

 one, into which the head is retractile, being the smallest. The 

 thoracic anterior inferior angles of the somites carry inconspicuous 

 minute bristly tubercules, while the abdominal segments, with the 



1889. 



