22 ILLINOIS BIOLOGICAL MONOGRAPHS (340 



and Phlebatrophia, the rrientum is strongly chitinized and flattened. 

 There is a distinct median longitudinal depression in Metallus. The 

 palpiger is practically wanting. The palpus is typically three-segmented 

 (Fig. 157). The relative size and structure of the segments vary, but are 

 usually constant for a subfamily or a genus. In Tremex and Phlebatrophia 

 the palpi are apparently two-segmented and very minute, while in Oryssus 

 they are obsolete. The stipulae are typically membranous, broad, some- 

 times bearing two setae, and fused with the mentum without any indication 

 of a suture. The stipulae are flattened and chitinized in Metallus and the 

 Fenusinae. Totaglossa is typically membranous, subglobose or bluntly 

 pointed, fused with the stipulae without any indication of a suture. It is 

 readily identified on account of its median position and characteristic 

 shape and structure. There is a slit-like opening for the duct of the silk- 

 gland, the sericos (crv) on the meson near the caudo-ventral aspect of the 

 totaglossa. The shape, size, and location of the sericos vary but it is 

 always present and chitinized. The cephalic or dorsal aspect of the 

 totaglossa is strongly convex, membranous, and sometimes bears a few 

 minute setae and sensoria. 



Prepharynx. — The prepharynx, the so-called "hypopharynx" of the 

 larvae of the Tenthredinoidea, is very simple in structure and the bound- 

 aries of the parts that can be identified in generalized insects (Yuasa, 

 1920) are obsolete. The propharynx consists of the epipharynx and epi- 

 gusta. The epipharynx is membranous, is of the same size and shape as the 

 labrum, and bears an oblique row of a few setae on each side slightly 

 dorsad of the ventral margin. The epigusta is membranous and is sup- 

 ported on each lateral portion by a torma. The ambipharynx is restricted 

 and membranous. The parapharynx consists of the basipharynx and 

 hypopharynx (hx). The basipharynx is subglobose or convex, often 

 slightly chitinized on the sides, sometimes having a few minute setae, 

 and usually converges ventrad. The portion ventrad of the constriction is 

 considered as belonging to the hypopharynx, but is usually membranous 

 and continuous with the Cephalic surface of the totaglossa without any 

 indication of differentiation. The laciniae fit against the sides of the 

 constricted part Of the parapharynx. No striking modification in form of 

 the prepharynx appears in the different families. 



Trunk. — The portion of the body caudad of the head is the trunk. 

 It consists of thirteen segments which connect with the head by means of 

 the cervacoria. The first three segments compose the thorax and the 

 remainder the abdomen. 



Cervacoria. — The membrane (cc) which connects the thorax with the 

 head is rather broad and usually folded under the protruding cephalic end 

 of the prothorax. There is a chitinized sclerite on each side, the cephalic 

 end of which articulates with the head against the odontoidea and the 



