38 ILLINOIS BIOLOGICAL MONOGRAPHS [38 



lateral projections are present in Lyctus (Fig. 546), Osmoderma (Fig. 553), 

 Parandra, Glycobius (Fig. 560), Rhynchites (Fig. 577), Epicaerus (Fig. 

 579), and Thecesternus (Fig. 581). Passalus (Fig. 556) is peculiar in the 

 possession of a large well chitinized secondary bridge arising from the 

 mesal margin of the mctatentoria. 



Owing to the simplicity of form of a structure like the corpotentorium, 

 but little change is indicated in it through most of the genera. The hypo- 

 thetical type shows this structure to be a rather narrow simple band (Fig. 

 443). Such is fairly characteristic of the vast majority of forms. The 

 corpotentorium is sometimes very broad, as in Ptinus (Fig. 543), Bostrichus 

 (Fig. 545), Parandra (Fig. 557), Derobrachus (Fig. 558), Glycobius (Fig. 

 560), and Eupsalis (Fig. 573). In contrast are many that are quite slender 

 and arched, as Dineutes (Fig. 452), Stenus (Fig. 463), Hister (Fig. 473), 

 Georyssus (Fig. 506), and Mycetophagus (Fig. 527). The form of these 

 latter has evidently resulted from the narrowing of the space between the 

 metatentoria. An exceptionally large number of genera have only a 

 rudimentary corpotentorium, or none at all, as in all of the Lampyroidea 

 except Trichodes (Fig. 479) and Necrobia (Fig. 480), Epicauta (Fig. 487), 

 Macrosiagon (Fig. 486), all of the Elateroidea, Psephenus (Fig. 502), 

 Rhysodes (Fig. 514), Phalacrus (Fig. 533), Hippodamia (Fig. 534), and Ar- 

 thromacra (Fig. 540). The reasons for the loss of the corpotentorium are 

 not always evident, though in most cases, either the arms of the tentoria 

 have expanded and approximately met on the meson, as in Rhysodes and 

 Plesiocis (Fig. 548), or the arms are directed towards the meson and meet 

 there, as in Connophron (Fig. 462) and all of the Elateroidea, or the 

 pharynx rests snugly between the tentorial arms, as is so perfectly found 

 in Chauliognathus (Fig. 477), where the pharynx is wedged so tightly 

 between them that the whole seems like one piece, all of which conditions 

 supply firmness to the tentorial arms and obviate the necessity for a corpo- 

 tentorium. Of the Rhynchophora, Eurymycter (Fig. 575), Epicaerus 

 (Fig. 579), Platypus (Fig. 583) and Lixus (Fig. 580) possess no corpoten- 

 torium. Scolytus (Fig. 584) possesses a very rudimentary one. The dis- 

 appearance of the corpotentorium can best be explained in the case of the 

 Rhynchophora by the fusion of the metatentoria into one solid plate that 

 needs no added support. The corpotentorium of most of the Cerambj-- 

 coidea is a delicate membranous structure. A common modification of 

 the corpotenterium is the mesal projections on its cephalic border, as in 

 Tachinus (Fig. 460), Cephaloon (Fig. 483), Tomoxia (Fig. 485), Phenolia 

 (Fig. 510), and Philothermus (Fig. 529). 



A structure of the tentorium that shows perhaps a greater variability 

 in form than any other is the laminatentorium, which appears in a great 

 array of shapes and sizes, from the forming of a perfect and broad bridge 

 to total disappearance. When the two sides of the laminatentorium meet 



