PROC. ENT. SOC. WASH., VOL. 24, NO. 1, JAN., 1922 23 



upward to the dorsal plane is a small spiracle on the eighth 

 pleurite, borne on a small backwardly-directed prominence. 

 The ninth urosegment is entirely membranous and is not 

 differentiated into tergite, sternite or pleurite. It encloses 

 the ovipositor, being everted when that organ is extruded. 



The eighth sternite is about two-thirds the length of the 

 seventh, about half as long again as wide, its sides subparallel 

 and rounded toward the apex. It is slightly narrower and 

 shorter than the eighth tergite. In fissilis Say the apical 

 margin is more or less acuminate medianly. The eighth 

 sternite is as heavily chitinized as the corresponding tergite. 



As in the male, the pleurites are membranous. The writer 

 has been unable to trace the alimentary tract of the female to 

 its anal opening. 



External genitalia of male (figs. 23, 24 & 25, M. communis 

 Gyll.) Throughout the genus the male genitalia are depressed 

 and consist of a basal piece (Bs) (orismology of Sharp and Muir) 

 which is chitinous and horse-shoe shaped, and encloses within 

 its open margin the bases of a slender median lobe (Mlb) and 

 two slender lateral lobes (Lib). The entire apparatus including 

 the basal piece and the three lobes is termed the aedeagus. 

 The basal piece is well chitinized on its lateral surfaces and on 

 its ventral face; the dorsal side of the median lobe and the entire 

 structure of the lateral lobes is likewise well chitinized. The 

 part within the horse-shoe of the basal piece, on its ventral 

 surface, the entire dorsal surface of the basal piece, and the 

 ventral side of the median lobe are membranous. The ejacula- 

 tory duct leads through the dorsal face of the basal piece to the 

 interior of the median lobe. The membranous ventral face 

 of the median lobe is perforated near its apex by the median 

 orifice (mo, fig. 24) through which the membranous internal 

 sac is everted when the apparatus is functioning. At such 

 time the membranous ventral surface of the lobe becomes 

 turgid, as does also of course, the everted internal sac. The 

 lateral lobes articulate laterally and are capable of opening at 

 nearly right angles to the median lobe. (Note. The orienta- 

 tion of the male genitalia is apt to be confused due to the fact, 

 that when fully exerted the aedeagus is bent upon the turgid 

 membranous structure which supports it, upward and forward, 

 and its surfaces become reversed, as shown in fig. 24. The 

 terms ventral and dorsal as here used refer to directions when 

 the genitalia are at rest within the body.) 



Valuable taxonomic characters have been found in the male 

 genitalia in the shape and relative slenderness of the median 

 lobe, and especially in the shape of the lateral lobes (see fig. 1). 

 One group of species (to which belong fissilis Say and co/mniviis 

 Gyll.) has the outer margin of the lateral lobe strongly angu- 

 lated near its apex; the second group (containing cribulosus 



