25] THE HEAD-CAPSULE Of COLEOPTERA—STICKXEV 25 



form. In just as wide a series of families, the epicranial arms are in 

 process of disappearing. In such cases, the caudal limits of the front can 

 only be judged approximately. In great reduction of the arms, as repre- 

 sented by Phalacrus (Fig. 96) and Macrosiagon (Fig. 49), the vertex, 

 the front and the postclypeus are indistinguishably fused into one area. 



In all species the clypeus is divided into two distinct sclerites, the 

 postclypeus and the preclypeus. This condition is not present so far as I 

 know in the more generalized insects such as the Orthoptera and Plecop- 

 tera. In some Neuroptera, however, the preclypeus is a large character- 

 istic sclerite, quite similar to what has been designated as the preclypeus 

 in the Coleoptera. It may possibly represent the extraordinary develop- 

 ment and differentiation of the labracoria, but its size, shape and form 

 would militate against such an assumption. It seems much easier to 

 believe that this area is a true sclerite, and in this discussion it will be so 

 considered. 



The broad cephalic part of the area between the epicranial arms in the 

 hypothetical type (Fig. 1) represents the postclypeus. In generalized 

 Coleoptera it is of considerable size if the dorsal surface has retained a 

 generalized form. The shape, form, and size of the postclypeus is cor- 

 related with the position and extent of the epicranial arms, which has 

 already been discussed. In highly specialized forms like the Scarabaeoidea 

 (Figs. 114, 115, and 116), the postclypeus may be even more extensive. 

 .-Vmong the Staphylinidae, the postclypeus may be very large in Tachinus 

 (Fig. 27) and Aleochara (Fig. 28), and very small in Creophilus (Fig. 26). 

 In Chalcophora (Fig. 357) the cephalic end of the vertex is located on the 

 ventral aspect of the head, and the postclypeus is reduced to hardly more 

 than a line. Among the Cerambycoidea the postclypeus is generally very 

 large. In the Rhynchophora it is quite reduced in size. 



The caudo-lateral projection or lobe of the postclypeus is the clypealia. 

 In Orthoptera and Plecoptera the clypealia is not separated from the re- 

 mainder of the postclypeus. In the larvae of CorydaHs it is a prominent 

 distinct sclerite. The clypealia in the Coleoptera is often separated from 

 the postch^peus proper by a distinct furrow or suture. It is quite loosely 

 attached to the postclypeus in the Cicindelidae (Figs. 297 and 298), the 

 Carabidae (Figs. 299 and 300), many of the Cerambycoidea (Figs. 419 and 

 424), and others. Difficulty is often experienced in removing the mandi- 

 bles from the head without detaching the clypealia. The close resemblance 

 between the Neuroptera and the Coleoptera in other respects would lead 

 one to beheve that this similar structure in the two orders must be ho- 

 mologous. The presence of this furrow in the Coleoptera is wide-spread, 

 as a glance at the figures will show. It can probably show little signifi- 

 cance as an indication of primitiveness. It must, though, have been 

 present in the primitive Coleoptera, and is hence shown in the hypothetical 

 type. 



