AMERICAN DIPTERA. 189 



border. On the tergal aspect the chitinous parts are interrupted 

 medially by a large triangular membranous area anteriorly, connect- 

 ing with a crescentic membranous area posteriorly (fig. 12). The 

 pleural lobes are large and strongly convex outwardly. Each is 

 somewhat more than twice as long as the body of the hypopygium, 

 and bears on the upper edge, near the distal end, a short, thick, ex- 

 panded, non- articulated lobe directed inward and forward. 



The guard of the penis is a flat plate, with the angles of the pos- 

 terior truncated end expanded laterally. The second gonapophyses 

 are large and densely chitinized processes (figs. 10 and 12, gon. 2) 

 projecting from the sides of the genital chamber above the guard. 

 The free part of each consists of two short thick arms, the inner 

 longer, serrate distally, and blackly chitinous. The two pairs are 

 connected medially by a short transverse process from each, the two 

 uniting to the middle line. Each gonapophyses has a long rod-like 

 apodeme extending forward into the abdominal cavity (fig. 10, op.). 



Genus LIM \ fOl'II 1 I, % Macq. 



In the structure of the hypopygium this genus differs in no essen- 

 tial manner from the genera, of the Eriopterina. It may be taken 

 as typical of Osten Sacken s fourth group, the Limnophilina. 



Lrimiiophila cubitalis O. S. (PI. IX, fig. 14). 



The hypopygium and genital chamber form a simple cup like 

 structure open dorsally and posteriorly. The ventral part of the 

 rim is somewhat produced posteriorly. 



From the floor of the genital chamber there projects upward and 

 posteriorly, at an angle of about 45 degrees, a short, thick, tubular 

 structure having a slender, chitinous, brace-like plate running out- 

 ward from it on each side. This is the penis and the first and sec- 

 ond gonapophyses. 



The penis itself, when divested of the ensheathing plates and 

 membranes, is seen to be a slender cylindrical tube, arising from an 

 enlarged base on the floor of the genital chamber, and extending 

 posteriorly and upward so that the tip, which is enlarged and bent 

 forward, projects out of the cavity (fig. 14, p). It is protected dor- 

 sally by two plates that arise near its base and converge and unite 

 upon its tip. Ventrally the penis is protected by two similar plates 

 arising below its base, converging upon the under surface of the tip, 

 but uniting here for a longer distance than do the dorsal plates. 



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



