37] THE HEAD-CAPSULE OF COLEOPTERA—STICKNEY 37 



straight arm toward the corpotentorium. The tremendous development 

 of the caudal part is due to the need of a strong support for the dorsal 

 surface, which bears a prominent horn used in fighting. 



The form and size of the metatentorium is quite decidedly indicated 

 by the position of the metatentorinae. Those genera possessing primitive 

 metatentorinae are very apt to possess the primitive type of metaten- 

 torium, one that is short and simple, as Limulodes (Fig. 469), Sphaerius 

 (Fig. 470), Anchicera (Fig. 5,?5), Philothermus (Fig. 529), Melanoph- 

 thalmus (Fig. 530), and Sphindus (Fig. 547). It is significant to note that 

 all of these genera are very small in size. The cephalic migration of the 

 metatentorinae is due to a similar movement of the metatentoria. In 

 those genera in which the metatentorinae have migrated from their primi- 

 tive position near the occipital foramen, the metatentoria are found more 

 or less deeply invaginated along the gular sutures, the sutures being the 

 products of these invaginations. In most genera the metatentoria advance 

 but little or not at all farther cephalad than the metatentorinae, but there 

 are some exceptions, in which the metatentoria taper gradually, as in 

 Helichus (Fig. 503), Cyphon (Fig. 509), Lyclus (Fig. 546), and all of the 

 Scarabaeoidea, except Pseudolucanus (Fig. 555). In those genera in 

 which the gular sutures are confluent on the meson, the gula itself is simply 

 invaginated, becoming a part of the metatentorium. The same type of 

 development has taken place in Necrophorus (Fig. 460), Scaphidium 

 (Fig. 471), Hister (Fig. 473), Phengodes (Fig. 470), Chauliognathus (Fig. 

 477), and Georyssus (Fig. 506), as in the Rhynchophora. In Necrophorus, 

 Phengodes, Chauliognathus, Eupsalis (Fig. 573) and Thecesternus (Fig. 

 581), the line of fusion of the invaginations of the two sides has disappeared. 

 In Chauliognathus the invagination is greatly reduced, and in Phengodes 

 nothing remains but a mere line. These two latter genera seem to show a 

 greater specialization of the gular region than any other genera studied. 

 A correspondingly deeper invagination of the ring-like plate surrounding 

 the inside periphery of the occipital foramen has occurred with that of the 

 gula. The whole phenomenon appears to be due to an especially strong 

 cephalic pull on the metatentoria. This can be readily understood in the 

 case of the Rhynchophora, in which the elongation of the snout would 

 encourage this result. A second force may play a part here, that of the 

 narrowing of the snout, which might assist in the enfoldment of the gula. 

 A large number of genera, scattered throughout the series of families, 

 possess prominent projections along the mesal margins of the metatentoria, 

 caudad of the corpotentorium, as those of Cybister (Fig. 451), Necrobia 

 (Fig. 480), Glischrochilus (Fig. 517), Phyconomus (Fig. 519), and Boros 

 (Fig. 539). Some of these projections have distinct tendons attached to 

 them, as in Scaphidium (Fig. 471), Parandra (Fig. 557), Derobrachus 

 (Fig. 558;, Donacia (Fig. 562), and Criocerus (Fig. 564). Prominent 



