AMERICAN DIPTERA. 271 



an opake spot. This cleft is sometimes provided with a 

 filiform appendage (Fig. 47) which often coaleses with the 

 bottom of the cleft in form of a vertical keel (Fig. 69). To 

 the left of the terminal lobe is the intermediate lobe (Fig. 49) 

 which is often invisible, being withdrawn into the fifth ab- 

 dominal segment ; it is never very much developed, and is only 

 distinguished from the terminal lobe by the vertical incisure 

 in form of a finely impressed line, which is one of the " two 

 dorso-ventral clefts ... to the left of the median line " men- 

 tioned by Dr. Hough in his description of P. atlanticus. To 

 the extreme base of the intermediate lobe, often ventral in 

 position, is the lateral lobe (Fig. 49), which is seldom visi- 

 ble, and is similar to the intermediate lobe, being separated 

 from it by an impressed line. At the extreme right of the 

 terminal lobe, and mostly ventral in position, is the ventral 

 lobe (Fig. 61), which at its base is probably the copulating 

 apparatus ; this lobe is most conspicuously developed in 

 Pipunculus atlanticus, and can at once be distinguished, espe- 

 cially when, as it often is, of a translucent yellow color. 

 Above, and at the extreme base of the terminal lobe, is the 

 basal lobe (Fig. 44), which is most strongly developed in 

 Verrallia, but indications of it can be seen in some specimens 

 of Pipunculus beneath the apical margin of the fifth segment. 

 The genitalia of the female is much more simplified, being 

 composed only of the more or less globose base, and the 

 aculeate ovipositor, at the base of which, beneath, is an open- 

 ing, revealed by a tuft of short hairs (Fig. 86). The pres- 

 ence or absence of the cleft in the terminal lobe of the males 

 is of much importance systematically, but it may be quite 

 variable in form in the same species, while in Pipunculus 

 atlanticus it may be quite distinct or hardly discernable ; 

 some times the entire hypopygium is extended so as to re- 

 veal the yellowish membrane between the different lobes. 



The femoral spines are the series of small black teeth or 

 spines on the flexor or under surface of the femora, being 

 more developed on the apical portion ; these spines are quite 

 distinct and in two rows, or, on the other hand, are hardly 

 distinguished under high magnification. 



TRANS. AM. ENT. SOC, XXXVI. DECEMBER, 1910. 



