18 ILLINOIS BIOLOGICAL MONOGRAPHS [336 



bicinae (Fig. 29) is unique in having a pair of longitudinal depressions on 

 each half which converge ventrad and bound a small median piece. 



Postgenae. — The area mesad of the lateral boundary of the vertex on 

 the caudal aspect of the head is the postgena {pa). The dorsal boundary 

 is the vertical furrow and the mesal the occipital foramen. The ventral 

 margin is concave and is connected with the labicoria {Ic). It is usually 

 more or less flat and glabrous. The occipital suture {os) is sometimes 

 distinct, as in Pteronidea. 



Tormae. — At each end of the clypeo-labral suture there is a chitinized 

 rod which extends onto the ventral surface as far as the epigusta. This is 

 the torma, present in all Tenthredinidae. 



Occiput. — The narrow area on the dorsal third of the occipital foramen 

 between the vertical furrows is the occiput. The dorsal boundary is in- 

 distinct since the occiput merges with the vertex without any indication 

 of a suture. 



Maxillariae. — The very narrow chitinized sclerites which form a sub- 

 circular collar around the dorsal and lateral margins of the occipital 

 foramen have been identified as the maxillariae {my). They are usually 

 only slightly developed and are continuous with the cervacoria. The 

 identity of these sclerites with the maxillariae of generalized adult insects 

 is uncertain, but they occupy the same position as the maxillariae and 

 consequently are considered as homologous with them. The dorsal third of 

 the maxillariae in the leaf-miners Metallus (Fig. 35), Phlebatrophia (Fig. 

 37) and Fenusinae (Fig. 34), are strongly chitinized, distinctly concave, 

 trough-like, and produced entad. Along this ental margin a part of the 

 muscles which control the movement of the head are attached. 



Occipital Foramen. — The large opening in the caudal aspect of the 

 head thru which the internal organs of the head are connected with those 

 of the body is the occipital foramen {of). The ventral margin of the 

 occipital foramen is membranous and connected directly with the laba- 

 coria and cervacoria {cc). 



Precoila. — The strongly chitinized acetabulum located near the 

 ventro-mesal angle of the vertex or the dorso-lateral angle of the clypeus 

 is the precoila {pr). The preartis of the mandible {py) articulates at this 

 point. The precoila is distinct in all Tenthredinoidea. 



Mandibularia. — The small transverse whitish or light-colored area 

 ventrad of the ventral margin of the head on the cephalo-lateral aspect is 

 the mandibularia {mb). It is usually only slightly chitinized and merges 

 with the mandacoria without any indication of a suture. The extensacuta 

 {ec) of the extensatendon of the mandible is usually distinct. The mandi- 

 bulariae are sometimes very large, as in the Xyelidae (Fig. 27). 



Postcoila. — The cup-shaped acetabulum on the latero-ventral angle 

 of the postgena and caudal angle of the mandibularia is the postcoila 



