TAXONOMY OF MUSCOIDEAN FUES — TOWNSEND 79 



representing" the front margin and the right angle cut off truncate 

 to represent the hind margin. 



The first segment consists above and on sides of a strip-like dorsal 

 plate evenly Repressed between its lateral edges, which are tucked-up 

 rounded folds of the plate, the latter ending ventrally on each side 

 in a short, pointed strip that does not meet the ventral plate, the ven- 

 tral membrane intervening between them. A small spiracle, smaller 

 than any of the others of abdomen, is present in the extreme point of 

 the first dorsal plate on each side where it joins the ventral mem- 

 brane, and each one of the other five dorsal plates has a similar but 

 larger spiracle on its inner edge, these being in each case quite well 

 removed from the lateral margin where it joins ventral membrane. 



The third ventral plate is nearly rectangular, a little broader than 

 long, about as wide as mean width of second plate. The fourth ven- 

 tral plate is considerably broader than the third and much shorter, 

 thus looking like a narrow transverse strip set in the ventral mem- 

 brane. The fifth ventral plate is much wider than fourth, about 

 same length, and its median portion (about middle one-third) ap- 

 pears to be crowded under the fourth plate by the walls of the 

 sheath-like genital opening, partially retracted within which lies the 

 hypopygium. Thus only the lateral one-third of the fifth plate is 

 visible on each side, and these two portions form the narrow visible 

 strips of the curved plate, bordering the edge of the genital opening 

 on each side, and each pointed at its outer extremity. 



The sixth abdominal segment is not apparent from a dorsal view. 

 It is a shortened anal segment that has been pushed over and 

 crowded beneath the extremity of the abdomen. It lies just under 

 the posterior edge of the abdomen, is rather crescent-shaped, sub- 

 semicircular on posterior (appearing anterior owing to inverted posi- 

 tion) edge where it encloses the basal segment of the hypopygium, 

 slightly squared on anterior lateral corners. It little more than half 

 surrounds the orifice of the genital cavity, and bears a spiracle on 

 each side at some distance before the pointed end of its tapering 

 lateral portion. The basal sclerite or plate of the hypopygium bears 

 another spiracle, which is one of the largest in the abdomen, on its 

 basal edge, near the spiracle of the sixth segment and appearing as 

 if it belonged to that segment. This basal plate of the hypopygium 

 represents another abdominal segment, and it should be considered 

 as forming a seventh segment of the abdomen rather than the base 

 of the hypopygium. 



The ventral membrane is widely apparent and extensive, the ven- 

 tral plates all lying free within it so far as contact with the dorsal 

 plates is concerned. The area in which the ventral membrane, with 

 6 



