312 Annals Entomological Society of America [Vol. XV, 



The epicranial suture is undoubtedly the most important landmark 

 on the head capsule of insects. In a discussion of the sclerites of the 

 head, therefore, it is logical to begin with this suture. This suture 

 is' the inverted Y-shaped median stricture found in nymphs, larvae and 

 generalized adult insects. It marks the line of closure of the head 

 during embryonic development. Originating at the occipital foramen, 

 it extends along the dorso-meson for some distance and gives rise to 

 two branches known as the epicranial arms. Each arm extends toward 

 a compound eye in generalized adult insects and to the cephalic margin 

 of the head in the case of larvae. The stem of the epicranial suture, 

 designated as the epicranial stem, is obsolete in all the species of 

 Mecoptera studied. In a hypothetical type of the mecopterous head, 

 the epicranial stem, as in generalized insects, originates from the 

 occipital foramen and extends cephalad and ventrad along the meson 

 and is interrupted at some point by the median ocellus. Emerging, 

 still as a single suture from the ventral margin of the median ocellus, 

 the epicranial stem extends ventrad of the antennariae, where it divides 

 into the epicranial arms, each arm extending laterad to a pretentorina 

 and then ventrad, terminating in a precoila. In Panorpodes (Fig. 1), 

 the epicranial arms (ea) are only partially present and the portion of 

 each arm extending from a pretentorina (pn) to a precoila (pr) is 

 obsolete. In Bittacus (Fig. 3), the entire epicranial arms are present 

 and in this respect Bittacus is more generalized than Panorpodes. In 

 Apterobittacus (Fig. 5), the transverse portion of the arms connecting 

 the pretentorinae has disappeared. In Merope (Fig. 7), the entire 

 epicranial suture is obsolete. In Panorpa (Fig. 10), on the other 

 hand, a portion of the arms is present and is, therefore, in this particular 

 more generalized than Merope. In Boreus (Fig. 14), the same con- 

 dition as in Merope obtains, the complete obsolescence of the epicranial 

 suture. 



The vertex (V, Figs. 1, 6, 14, 16, 19, 27, 28) extends from near 

 the occipital foramen (of. Figs. 16, 19, 22) and ventrad to the sutures 

 marking the boundary of the sclerites of the ventral portion of the head. 

 In generalized insects, as the cockroach, the vertex is a paired sclerite, 

 being divided along the meson by the epicranial stem. The vertex 

 in the Mecoptera is a solid piece, not a paired sclerite, on account of 

 the obsolescence of the epicranial stem. It bears, besides the com- 

 pound eyes, the ocelli and the antennae (a). Each lateral portion of 

 the vertex is greatly prolonged ventrad in Boreus and Panorpa. There 

 is a tooth-like lateral projection of the vertex in Bittacus, Aptero- 

 bittacus, Merope and Panorpodes which is especially prominent in 

 the species of the last named genus. This projection seems to be 

 wanting in Panorpa and Boreus, but its homologue can be identified 

 in these last two genera. 



The fronto-clypeus (fc), formed by a fusion of the front and clypeus 

 through the obsolescence of the fronto-clypeal suture, is, roughly 

 speaking, subquadrate in Panorpodes (Fig. 1), Bittacus (Fig. 3), Aptero- 

 bittacus (Fig. 5), and Merope (Fig. 6), and rectangular and greatly 

 elongated in Panorpa (Fig. 10) and Boreus (Fig. 14). It is in general 



