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



a fovea enters more or less sideways the external face of the 

 mandible near its base (Mnd fov, fig. 3); this fovea varies in 

 shape and size, and is entirely absent in about half of the 

 known American species, including communis Gyll. andjissi/zs 

 Say. The prostheca (prs. figs. 7 & 8) is broadly rounded, 

 pubescent along its free margin and prominent when the 

 mandible is extended. In the species examined its superior 

 surface is shiny except for an opaque, suboval area near its 

 base. The flexor muscle (fix, figs. 7 & 8) is strongly developed 

 and is attached along the middle of the basal margin; the 

 weaker retractor muscle (rtr, figs. 7 & 8) used only in opening 

 the mandible is attached in the condylar fossa. The posterior 

 condyle (pc, fig. 8) is strongly developed and with its articula- 

 tion forms a ball-and-socket joint. The anterior condyle 

 (ac ; figs. 7 & 8) is less prominent; it bears a shallow longitudinal 

 depression on its side along the fossa, into which the condyle 

 of the clypeus fits. 



Throughout the genus, as far as the writer has examined, 

 the mental suture (mt sut, fig. 2) lies just back of a sharp, anteri- 

 orly deflexed carina which forms the posterior margin of the 

 submentum. The outline of the gula (fig. 2) is clepsydral 

 (resembling an hour-glass) being strongly constricted behind 

 its middle. The gula is declivous on its anterior part from the 

 mental suture to its narrowest point; the part behind the con- 

 striction is sharply raised above the plane of the narrowest part 

 of the sclerite. 



Labium (figs. 2 & 9, M.fissilis Say). Except for its sharply 

 carinate, anteriorly recurved posterior margin, the submentum 

 (Smt, figs. 2 & 9) is evenly and deeply depressed as compared 

 with the gula. It bears two pairs of long, converging, anteriorly 

 directed hairs; its posterior margin is sinuate; its sides anteriorly 

 convergent, rising posteriorly to meet the level of the posterior 

 margin. The mentum (Mt, figs. 2 & 9) is semi-membranous, 

 its sides continuing the line of the submentum, and its anterior 

 margin nearly truncate with a small sinuation curving between 

 the bases of the palpigers. The ligula (Lgl, figs. 2 & 9) is mem- 

 branous, broadly triangular, with a median slit extending nearly 

 to its base; its anterior margin bears a fine pubescent fringe. 

 There is no trace of the paraglossae. 



The buccal side of the ligula (fig. 10) is thickly covered with 

 short bristly hairs in communis Gyll. About half way down 

 the buccal face the slit ends in a semi-chitinous point. From 

 this point down along the median line toward the base is a 

 prominent carina which is accentuated by a thick fringe of 

 medianly directed hairs which curve upward from the bottom 

 of a concavity lying on either side of the median line. This 

 heavily pubescent carina ends posteriorly in a shallow depres- 

 sion which separates it from the hypopharynx (hyp. fig. 10). 



