35] THE HEAD-CAPSULE OF COLEOPTERA—STICKNEY 35 



readily be recognized by their characteristic form. Since they are always 

 located on the caudo-lateral lobe of the postclypeus, or the clj-pealia of 

 certain insects, they are a great aid in determining the limits of the post- 

 clypeus. 



The endoskeleton of the head is known as the tentorium. It is com- 

 posed of two anterior and two posterior areas or projections, and their 

 various modifications. The anterior arms arise from the pretentorinae, 

 and are known as the pretentoria. The posterior arms arise from the 

 metatentorinae, and are known as the metatentoria. In generalized in- 

 sects one end of the pretentorium expands along and is continuous with the 

 epicranial suture. Each extends in a caudo-mesal direction, and narrows 

 for a short distance, then expands along its mesal margin until a fusion 

 is formed with the pretentorium of the other side, producing the cephalic 

 bridge, or laminatentorium. The pretentoria separate and then fuse 

 again farther caudad with each metatentorium. The metatentoria ex- 

 tend cephalo-mesad a very short distance, their mesal margins expand 

 and completely fuse on the meson, producing the caudal bridge or corpo- 

 tentorium. The fusion of the pretentoria and the metatentoria is sup- 

 posed to take place along the cephalic margin of the corpotentorium. 

 The dorsal projections arising from the lateral margins of the pretentoria 

 and extending toward and attached to the dorsal wall of the head, are 

 the supratentoria. The ring-like plate surrounding the inside periphery 

 of the occipital foramen is indistinguishably fused with and is a part of the 

 metatentoria. The tentoria, as a whole, are distinctly chitinized and well 

 developed. The tj^jical condition of the tentorium in generalized insects 

 is practically duplicated among the Coleoptera. The hypothetical type 

 (Fig. 443) has been constructed with this similarity in mind. The greatest 

 difficulty experienced was in deciding upon the primitive type of lamina- 

 tentorium, whether it should be represented as complete or incomplete, 

 that is, whether the two sides of the laminatentorium fuse on the meson 

 or not. Many Coleoptera that in other respects are quite generalized do 

 not show a complete laminatentorium, as Tetracha (Fig. 444), Omophron 

 (Fig. 449), Dineutes (Fig. 452), Leptinus (Fig. 459), Tachinus (Fig. 460), 

 and Stenelmis (Fig. 504). The hypothetical laminatentorium is repre- 

 sented as nearly meeting on the meson. At least, such a condition is 

 thought to be not far removed from that which actually existed in the 

 primitive Coleoptera. Limulodes (Fig. 469), Eurystethus (Fig. 488), 

 Pytho (Fig. 490), Philothermus (Fig. 529), Melanophthalmus (Fig. 530), 

 Hyporphagus (Fig. 541), Sphindus (Fig. 547), and others, possess practi- 

 cally no trace of a laminatentorium, but well developed supratentoria. The 



atter are fairly well developed in Photinus (Fig. 475), Collops (Fig.'478), 

 and Alaus (Fig. 498), but there is neither a laminatentorium nor a corpo- 



entorium present. There is no trace of any one of the three 'above 



