18 ILLINOIS BIOLOGICAL MONOGRAPHS (18 



very distinct and sharply invaginated in both, particularly so in the former, 

 and characteristic in form. Each arm reaches the margin of the head 

 almost immediately cephalad of a compound eye, and the arms are not as 

 generalized in position as they are in Epicauta (Fig. 50), where they are 

 quite distinct. The only other occurrence of a complete epicranial suture 

 is in Chelymorpha (Fig. 134). Here the arms meet the stem farther caudad 

 than in the other genera named. The arms in this last genus are distinctly 

 curved, as contrasted with the more or less straight arms in the above 

 mentioned genera. 



The epicranial arms or some portion of them are present in all Coleop- 

 tera, except possibly in Calopteron (Fig. 36) and Photinus (Fig. 37). 

 One or more species of every superfamily of the Adephaga and Polyphaga, 

 except the Elateroidea,Byrrhoidea, Rhysodoidea,and Rhynchophora, have 

 the arms complete. In the Caraboidea they are prominent as nearly 

 straight sutures across the head, as in Tetracha (Fig. 2), Cicindela (Fig. 3), 

 Calosoma (Fig. 4), and Harpalus (Fig. 5). Their most generalized condi- 

 tion in the Adephaga is found in Omophron (Fig. 7) in which they extend 

 from the meson at a sharp angle. Representative species of other super- 

 families that have the arms complete are: Necrophorus (Fig. 18), Tachinus 

 (Fig. 27), Chauliognathus (Fig. 39), Cupes (Fig. 45), Cephaloon (Fig. 46), 

 Notoxus (Fig. 56), Heterocerus (Fig. 68), Eucinetus (Fig. 71), Myceto- 

 phagus (Fig. 90), Tenebrio (Fig. 101), Bostrichus (Fig. 108), Aphodius 

 (Fig. 112), and nearly all the Cerambycoidea. Species having parts of the 

 epicranial stem preserved are not very common. In Omophron (Fig. 7), 

 Tachinus (Fig. 27), Penthe (Fig. 105), and a number of the Cerambycoidea, 

 parts of the cephalic end can be identified; in Omophron (Fig. 7), Phengodes 

 (Fig. 38), Cupes (Fig. 45), Sitodrepa (Fig. 107), Blepharida (Fig. 132), 

 and a number of the Rhynchophora, parts of the caudal end are present. 

 Chalcophora (Fig. 64) and Tetraopes (Fig. 124) are peculiar in possessing 

 practically all of the stem but little of the arms. The arms in Chalcophora 

 are as short as in any other species studied. Parts of the arms are present 

 in every degree of length from nearly meeting on the meson, as in Nosoden- 

 dron (Fig. 76), to almost complete disappearance as in Chalcophora (Fig. 

 357) and Rhysodes (Fig. 370). They also show varying degrees of dis- 

 appearance and invagination, from the deep distinct invaginations of 

 such forms as Dineutes (Fig. 10), Necrophorus (Fig. 18), Tachinus (Fig. 

 27), Heterocerus (Fig. 68), and Arthromacra (Fig. 103), to the faint or 

 slender and shallow or not at all invaginated sutures characteristic of the 

 Scarabaeoidea. 



The character of the invagination associated with the epicranial arms 

 is not as simple as may be thought. In Harpalus (Figs. 5 and 24), the 

 epicranial arms extend from the meson along the edge of the invagination 

 to the pretentorinae, from which they extend to the bottom of the invagi- 



