34 ILLINOIS BIOLOGICAL MONOGRAPHS [34 



Sitodrepa (Fig. 255), and Plesiods (Fig. 259). Part of it is deeply in- 

 vaginated transversely in Scaphidium (Fig. 179), Chauliognathus (Fig. 

 185), Helichus (Fig. 214), Stenelmis (Fig. 215), and others. 



Most of the sclerites of the head-capsule are so closely united in some 

 Coleoptera as to appear as a single piece. Strauss-Durckheim (1828) so 

 regarded this region in the head-capsule of the May-beetle, and named it 

 the epicranium. Used in the sense of indicating a closely united area, 

 the term seems satisfactory and may often prove convenient. It can then 

 be only a relative term, including at times no more than the paired sclerites 

 of the head, when the epicranial suture is well developed. Occasionally, 

 the preclypeus and the labrum are closely joined to the head-capsule. 

 In such cases, the epicranium would embrace these structures, also. 



The small rather concave projections at the caudo-mesal margins of 

 the postgenae against which the maxillae articulate are the paracoilae. 

 They are usually easily identified, as in Molamba (Fig. 169), Pytho (Fig. 

 201), Heterocerus (Fig. 216), and Phymaphora (Fig. 242). They are 

 usually chitinized, but are membranous in a considerable number of genera. 

 The paracoilae are insignificant in size in Gastrolobium (Fig. 171), all of 

 the Elateroidea, Pseudocistela (Fig. 247), and Tenebrio (Fig. 249). In 

 generalized insects the paracoilae are situated beneath the submentum. 

 They are found in a similar position in the Adephaga (Figs. 150, 152, 154, 

 157, and 158), in Hydrous (Fig. 161), and a few others. They are also 

 always located on the postgenae in generalized insects. This position is 

 of great importance in determining the identity of the postgenae in special- 

 ized insects. 



At the cephalic end of a postgena is always found a distinct crescent- 

 shaped acetabulum — the postcoila, against which the postartis of the 

 mandible articulates. Throughout the genera the postcoilae exhibit 

 some degree of difference in exact position upon the postgenae, in size, 

 and in degree of shallowness. Their form and position are indicated in 

 Calosoma (Fig. 152), Sphaerius (Fig. 178), Notoxus (Fig. 204), and Dero- 

 brachus (Fig. 269). In generalized insects the postcoilae are also always 

 located on the postgenae, and their position is of equal importance with 

 that of the paracoilae in determining the identity of the postgenae. 



The rounded condyle on the ventral surface of each clypealia, against 

 which the preartis of the mandible articulates is the precoila. It is usually 

 crescent-shaped, but sometimes, as in Peltodytes (Fig. 156), Cybister 

 (Fig. 157), Creophilus (Fig. 172), Endomychus (Fig. 243), Dichelonyx 

 (Fig. 261), and others, the form is spherical. The precoilae are large in 

 Macrosiagon (Fig. 197), Epicauta (Fig. 198), Isorhipis (Fig. 210), Chauliog- 

 nathus (Fig. 185), Bostrichus (Fig. 256), and others, and small in Dineutes 

 (Fig. 158), Photinus (Fig. 183), Helichus (Fig. 214), Derodontus (Fig. 

 235), and particularly so in Psephenus (Fig. 213). The precoilae can 



