36 ILLINOIS BIOLOGICAL MONOGRAPHS [36 



mentioned structures in Isorhipis (Fig. 499) and Throscus (Fig. 500). Phal- 

 acrus (Fig. 533) and Eurymycter (Fig. 575) possess only the rudiments of 

 the pretentoria and metatentoria. The tentoria of the Cerambycoidea 

 (Figs. 557, 560 and 566) are very delicate and membranous. The preten- 

 toria, the metatentoria, and the corpotentorium are always complete, while 

 the laminatentorium and supratentoria are always either rudimentary or 

 absent except in Pachymerus (Fig. 572) in which the supretentoria are 

 present. Other genera showing completely membranous tentoria are 

 numerous. Among these are Cupes (Fig. 482), Eurystethus (Fig. 488), 

 Rhysodes (Fig. 514), Languria (Fig. 522), and Pseudocistela (Fig. 536). 



A generalized condition of the pretentorium, characterized by a strong 

 chitinization as a whole, and possessing a broad flaring cephalic end, is 

 found in the Adephaga (Figs. 449 and 451), Leptinus (Fig. 459), Necro- 

 phorus (Fig. 460), the Staphylinidae (Figs. 465 and 467), Georyssus (Fig. 

 506), Eucinetus (Fig. 508), Dermestes (Fig. 511), and Derodontus (Fig. 

 524). There are all degrees of gradation present from the most generalized 

 pretMitoria to those very delicate membranous ones represented by such 

 forms as Heterocerus (Fig. 505), Endomychus (Fig. 532), Pseudocistela 

 (Fig. 536), Hyporphagus (Fig. 541), the majority of the Cerambycoidea, 

 and the Rhynchophora. A very prevalent tx-pe, possessing a distinctly 

 chitinized cephalic end and a membranous caudal portion sharply sepa- 

 rated from the former, is represented in Epicauta (Fig. 487), Pytho (Fig. 

 490), Chalcophora (Fig. 501), Alobates (Fig. 536), Bostrichus (Fig. 545), 

 Diabrotica (Fig. 568), Dendroctonus (Fig. 585) and most of the Scara- 

 baeoidea. Rudimentary pretentoria are found in a number of genera, as 

 Calopteron (Fig. 474), Tenebroides (Fig. 515), Phalacrus (Fig. 533), 

 and perhaps all of the Rhynchophora, except Dendroctonus. The pre- 

 tentoria of the Rh3'nchophora are for the most part very delicate and 

 fragile. The difficulty of making a dissection showing the pretentoria 

 intact is intensified by the close packing within the snout of the greatly 

 developed tendons of the mouth-parts and the strongly chitinized pharynx. 

 In no instance, except in Dendroctonus was a pretentorium preserved 

 intact. In Scolytus (Fig. 584), the pretentorium is evidently rudimentary, 

 but in none of the other genera is there a clear indication of such being the 

 case, owing to the presence of frayed ends, suggesting that not all of the 

 pretentorium has been seen. The presence in the Rhynchophora (Figs. 

 433, 435, 437, 439 and 441) of a suture in the right position for an epi- 

 cranial suture, an invagination within the suture that suggests the preten- 

 torina, and a projection arising from the invagination, all furnish evidence 

 that this projection is probably the cephalic portion of the pretentorium. 

 The pretentorium of Passalus (Fig. 413) is extraordinarily developed. 

 The cephalic part extends as a slender bar dorso-caudad, nearly half way 

 to the occipital foramen, then bends suddenly and extends as a huge 



