AMERICAN DIPTERA. 215 



slender, blade like plate extends caudally, the two having their flat 

 surfaces apposed and vertical. Below their bases there projects ven- 

 trally and posteriorly, from the ventral surface of the guard, a trans- 

 verse, pointed, chitinous process. 



Tipiila inermis Doane (PI, XIII, figs. 89, 90, 91, 92, 93). 



The eighth sternum is large, prolonged posteriorly and armed at 

 the posterior end. The posterior border of the sternum is deeply 

 eraarginate (fig. 92). At each side of the emargination is born a 

 large, three-sided, conical lobe (a) attached by its apex, similar to 

 that of Tipida ceqitalis. The flat bases of these lobes are turned 

 upward and inward. The dorsal angles of the bases are connected 

 by an arched bar of chitin lying in a membranous fold above. At 

 the apex of the notch of the sternum is a wide, rounded, plate-like 

 lobe (6) projecting posteriorly and ventrally. On each side of it 

 there projects posteriorly a long arm-like process (c). From each 

 inner ventral angle of the conical lobes (a) a pencil of hairs projects 

 inward and ^posteriorly. 



The hypopygium is somewhat flattened upon the end of the abdo- 

 men (fig. 91). The sternum is divided by a y-shaped notch almost 

 to its anterior margin. In front of the apex of the emargination is 

 a membranous area, and in front of this is a chitinous bar connect- 

 ing the lateral chitinous parts. There is a submarginal suture along 

 each side of the notch, and the two separate off" a V-shaped marginal 

 lobe. Each posterior end of the latter forms a small knob support- 

 ing a bunch of hairs. Laterad of this there is a hook shaped ap- 

 pendage on each side arising from the sternal margin (fig. 91, d). 

 There is a well developed triangular plate on each side, separated by 

 an angular suture from the lateral part of the sternum. 



There are three apical lobes, all of them arising from a common 

 base (fig. 89). The first (A) is small, flat and spatulate. It arises 

 from the anterior part of the base of the second. The first very 

 commonly arises close to the base of the second, but it is seldom 

 attached almost to the side of it as in this species. The second ap- 

 pendage (B) is large and flat. Distally it is expanded and produced 

 into a blunt point posteriorly and a sharper one anteriorly. The 

 anterior margin below the lobe is reflexed posteriorly over the outer 

 side. The third appendage (,C) is a short slender arm arising from 

 the posterior edge of the base of the second. 



TRANS. AM. ENT. SOC. XXX. JULY. 1904. 



