26 ILIjyOIS BIOLOGICAL MONOGRAPHS [26 



In most of the Orthoptera a small triangular area is present, extending 

 from the precoila to the cephalic end of the occipital suture. This sclerite 

 is known as the mandibularia. No such area has been located in the 

 Coleoptera. 



The dorsal surface of the larvae of Corydalis is very generalized. On 

 this surface there is a prominent submembranous sclerite between the 

 postclypeus and the labrum, the preclypeus. Such a sclerite, very similar 

 in size, form, texture, and position, is present in Tachinus (Fig. 27), 

 Arthromacra (Fig. 103), Trichodes (Fig. 41), and Glycobius (Fig. 123). 

 This sclerite is considered the preclypeus. Figure 23 is a longitudinal 

 section of the dorsal aspect of the head of Harpalus, and shows the char- 

 acteristic position of the preclypeus. It is always present in the Coleop- 

 tera, though often considerably reduced in size. The precl}-peus is al- 

 waj's membranous except in Photinus (Fig. 37), where it is chitinized 

 and the labrum is membranous. Besides the forms mentioned above, 

 the preclypeus is large and prominent in Necrophorus (Fig. 18), Conno- 

 phron (Fig. 20), Macratria (Fig. 55), Philothermus (Fig. 92), Hippodamia 

 (Fig. 97), and many others. Very frequently the cephalic end of the 

 postclypeus is infolded, thus carr\-ing the preclypeus and the labrum with 

 it. In such cases the prech'peus cannot be seen from the dorsal aspect. 

 The preclypeus, no matter how deeply it is infolded, is, except in a few 

 cases, sharply differentiated from the postclypeus and the labrum. In 

 GHschrochilus (Fig. 373) and Chauliognathus (Fig. 332) the postclypeus 

 and the labrum were in such close approximation that the preclypeus could 

 not be observed until the two above mentioned scJerites were separated, 

 and this was possible only after long soaking in potassium hydroxide. 

 In most of the Rhynchophora, due to the fusion or absence of the labrum, 

 the preclypeus could not be identified. The preclypeus, however, was 

 prominent in Attelabus (Fig. 141), and somewhat reduced in Epicaerus 

 (Fig. 290). 



The broad prominent sclerite attached to the cephalic end of the 

 clypeus in generalized insects is the labrum. In Coleoptera possessing 

 other generalized structures, the labrum is typically of the same general 

 form. The labrum is shown in the hypothetical type. In position the 

 hypothetical labrum should be, with the preclypeus, in accordance with 

 their condition in generalized insects, on the same general level with the 

 remainder of the dorsal surface. The generalized form and position of 

 the labrum is present iti every superfamily except the Elateroidea, 

 Dryopoidea, Rhysodoidea, Scarabaeoidea, and the Rhynchophora, in 

 which the postclypeus has been infolded, thus forcing the labrum onto 

 the ventral aspect. All the superfamilies containing species with the 

 labrum generalized, contain about as many with it in various degrees of 

 specialization, as to form, size, texture and position. The labrum in Con- 



