20 ILLIXOIS BIOLOGICAL MONOGIiAPlIS [20 



the vertex and the front. It is obvious from the above discussion of three 

 types of the invagination associated with the epicranial arms that the 

 dorsal surface of the head-capsule in Coleoptera must be studied most 

 carefully before a correct interpretation of the parts can be made. This 

 is most true in the case of any invagination that may be present. The 

 latter may not be readily observed when the head-wall is strongly and 

 darkly chitinized, necessitating treatment of such specimens before the 

 parts can be clearly made out. In Dermestes (Fig. 74), and perhaps others, 

 all external trace of the line of the invagination may be lost. In such 

 cases a true understanding of the parts can only be gained from an ex- 

 amination of the ental surface of the head. But in specialized forms the 

 ental indication of the invagination may also be effaced. 



The epicranial suture can always be located from the determination of 

 the position of the pretentorina. The latter is always closely associated 

 with the epicranial suture, being present either in or just oft" of the suture, 

 in which case the pretentorina resembles a sort of pocket. There is 

 usually little difficulty experienced in locating the suture. The cephalic 

 ends of the arms are the most persistent parts of it, being present when 

 the remainder of the suture cannot be identified. Interesting examples 

 are found in most Rhynchophora, where the remnants of the epicranial 

 arms are represented by short furrows located at the cephalic end of the 

 snout. The epicranial arms are typically structures of the dorsal aspect, 

 but with the shifting and modification of other parts of the head may be 

 confined to the lateral aspect, as in Helichus (Fig. 359), Adalia (Fig. 391), 

 or to the ventral aspect, as in Cybister (Fig. 157), Hydrous (Fig. 161) 

 and Phalacrus (Fig. 244). From the preceding discussion of the epicranial 

 suture it is seen that what appears superficially to be this suture may not 

 be so. It is a difficult problem to understand the kind and amount of 

 change that may have taken place. In a number of the Rhynchophora, 

 for instance, what appears to be the epicranial stem (Figs. 146 and 147) 

 may be only invaginations, for in these same species are lateral invagina- 

 tions that are quite similar in form to the so-appearing epicranial stem. 

 The epicranial stem seems to the writer to hold the strongest claims, so 

 these invaginations are considered as such. So, in other instances, where 

 a structure appears to be more definitely the epicranial suture than any- 

 thing else, it is so interpreted. 



That part of the head-capsule not embraced by the three primary 

 sclerites cephalad of the epicranial arms, the occiput, and the postgena, 

 constitutes the vertex. Its extent is determined by the form and size 

 of the three above mentioned areas. For instance, in those species with 

 much reduced epicranial arms, as in Creophilus (Fig. 26), Adalia (Fig. 98), 

 and Phalacrus (Fig. 96), the extent of the vertex is correspondingly in- 

 creased. In the Rhynchophora, as represented by such species as Lixus 



