16 ILLINOIS BIOLOGICAL MONOGRAPHS [334 



(Fig. 45), where it is in part indistinct, and in the Siricidae and Oryssidae, 

 where it is obsolete. It is interesting to note that the most highly special- 

 ized genus of the Tenthredinidae, Phlebatrophia (Fig. 37), possesses this 

 suture. The relative length of the stem and arms varies in different 

 families and subfamilies. There is a depression near the bend of the arm, 

 as in Lygaeonematus (Fig. 31), which indicates the point of attachment of 

 muscles {ma), and should not be confused with a true tentorina (/>«). 

 Near the ventral end of each epicranial arm there is a thickening of the 

 surface and a pit. This pit is a pretenorina {pn) and the thickened piece 

 corresponds to the clypealia {d) of the larva of Corydalis. The preten- 

 torina and clypealia are constant in position and universal in occurrence in 

 the Tenthredinoidea. In the Siricidae the pretentorinae are distinct and 

 sometimes mistaken for ocellarae. In ecdysis the head is split along the 

 epicranial suture nearly to the ventral ends of the arms. 



Vertex. — The large area on each side of the epicranial stem is the vertex 

 (»). It extends from the dorso-meson of the epicranium to the ventral 

 margin of the head, laterad of the epicranial arm, and cephalad of the 

 occipital suture when this is present, and bears an ocellara {o) and anten- 

 naria (ar). There is on the dorsal part of the vertex on each side a distinct 

 furrow which originates at the occipital foramen and extends cephalad 

 for some distance onto the lateral aspect of the head. This is the vertical 

 furrow {vf) and is characteristic of the larvae of the Tenthredinoidea. 

 It is wanting only in the leaf-miners and wood-borers. The nature of this 

 furrows is not known. There is a corresponding carina on the ental sur- 

 face of the head, and the major muscles of the retractor of the mandible 

 are attached to the ental surface of the vertex dorsad and ventrad of the 

 vertical furrow. The furrows usually converge at the cephalic end, but 

 sometimes are subparallel to each other. 



Genae. — The portion of the vertex ventrad of an imaginary line drawn 

 ventrad of each ocellara parallel to the ventral margin of the head is a 

 gena (g). The extent of the genae varies, therefore, according to the 

 location of the ocularia. The setae on the genae are sometimes longer 

 than those elsewhere. 



Ocularia. — The larvae of the Pamphiliidae, Xyelidae, Tenthredinidae, 

 and Cephidae possess a pair of ocellarae (e), one on each side of the head. 

 These organs of sight are remarkably uniform and constant in structure 

 and location. With the exception of Phlebatrophia and the Cephidae, the 

 ocellarae are usually clear, semiglobose or at least distinctly convex, 

 and are located on or near the center of the ocularia {ou), which are usually 

 circular and distinctly blackish. The ocularia are located on the vertex 

 dorsad of the antennariae in the Tenthredinidae and caudad of them 

 in the Pamphiliidae and Cephidae. In the Cephidae and Phlebatrophia 

 the ocularia are obsolete and the ocellarae are indicated by pigmented 



