19) THE HEAD-CAPSULE OF COLEOPTERA—STICKNEY 19 



nation, curve laterad, and continue to the margin of the head. The course 

 of the epicranial arms can be better understood from Omophron (Fig. 7), 

 a related genus, which has retained the cephalic portion of the epicranial 

 stem. The line of the invagination appears to be and often is considered 

 to be simply the clypeal suture. If a specimen of Harpalus is soaked for a 

 long time in potassium hydroxide the invagination can be opened and the 

 various structures in this region studied advantageously. The invagina- 

 tion when opened (Fig. 24) will be seen to assume a deep wide wedge- 

 shaped form, extending entirely across the dorsal surface of the head. The 

 pretentorinae are located on the external dorsal surface just caudad of the 

 cephalic margin of the invagination. Although the epicranial arms are not 

 in evidence anywhere between the meson and the pretentorinae, it is 

 assumed that the cephalic marginal ridge must represent them, since the 

 pretentorinae are not only located caudad of the invagination, but the 

 arms are quite distinct, extending from the pretentorinae to the bottom 

 of the invagination, in which they then curve laterad and continue to the 

 margin of the head. From a cross-section (Fig. 23) it will be seen that the 

 pretentorium expands cephalad in characteristic form from the preten- 

 torina along an epicranial arm to the bottom of the invagination. In 

 Calosoma (Fig. 4) the same condition of this region is found as in Harpalus. 

 In Omophron (Fig. 7) the epicranial arms are distinct between the preten- 

 torinae, extending from the meson along the cephalic border of the invagi- 

 nation. From Figure 24 it will be observed that the cephalic border of the 

 invagination in Harpalus is along the imaginary line of the fronto-clypeal 

 suture. This border may represent the cephalic limit of the front. The 

 invagination, then, in Harpalus and Calosoma includes the entire front. 

 The line of the invagination instead of being solely a part of the epicranial 

 suture is in fact compound in nature, representing the approximation 

 of the caudal borders of the front and postclypeus, and that part of it 

 between the pretentorinae may be termed the "clypofrons." Laterad of 

 the pretentorinae to the margin of the head the line of the invagination is 

 readily seen to be an approximation of a part of the vertex with the caudal 

 border of the postclypeus and cannot be included in the clypofrons. 

 Due to the more primitive position of the epicranial arms in Omophron 

 the invagination in this genus contains only a part of the front, hence the 

 line of the invagination between the pretentorinae is simple in nature. 

 In Tachinus (Fig. 27) the epicranial stem extends distinctly into the in- 

 vagination, the arms continuing in the same to the margin of the head. 

 .\s should be expected, the pretentorinae are within the invagination. 

 The line of the invagination in Tachinus is then of a different character 

 from that of either Harpalus or Omophron. In Tachinus, it has nothing 

 whatever to do with the epicranial suture nor with any other suture, being 

 throughout the approximation of parts of the external dorsal surface of 



