OR1SMOLOGY, 335 



III. TRUNK (TRVNCUS). 



1. MONOMEROUS (Monomerus). When the trunk has 



no suture or segment. Ex. Araneidea. 



2. DIMEROUS (Dimerus). When the trunk consists of 



two greater segments. Ex. Coleoptera, Sac. 



3. TRIMEROUS (Trimerus). When the trunk consists 



of three greater segments. Ex. Neuroptera, &c. 



4. ISTHMIATE (Isthmiatus). When an isthmus is formed 



between the Prothorax and Elytra, either in con- 

 sequence of the former being constricted behind 

 so as to form a neck, or the scutellum not being 

 interposed between the elytra at their base, or the 

 chief part of the mesothorax not being covered by 

 the prothorax. Ex. Clems, Passalus, and Spon- 

 dylis. 



i. MANITRUNK (MANITRUNCUS}. 



a. PROTHORAX. 



1. CLYPEIFORM (Clypeiformis). When the prothorax 



by its magnitude and distinct separation forms one 

 of the most conspicuous pieces of the upper side of 

 the trunk, so as nearly to represent the whole 

 thorax; the mesothorax and metathorax being 

 mostly hidden by the elytra and other organs for 

 flight. Ex, Coleoptera, Qrthoptera, &c. PLATE 

 VIII. FIG. 1, 10. 



2. COLLIFORM (Colliformis). When the prothorax is 



short and narrow, and not so conspicuous as the 

 other pieces of the trunk. Ex. Libellulina. 

 PLATE IX. FIG. 6. 



