OR1SMOLOGY. 335 
/ 
III. TRUNK (Truncus). 
1. Monomerous (Monomerus). When the trunk has 
no suture or segment. — Ex. Araneidea. 
2. Dimerous (Dimerus). When the trunk consists of 
txvo greater segments. — Ex. Coleoptera, &c. 
3. Trimerous (Triments). 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. Clerus, Passalus, and Spon- 
dylis. 
i. MANITRUNK {Manitruncvs). 
a. PROTHORAX. 
1. Clypeiform (Clypeiformzs). 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 j the mesothorax and metathorax being 
mostly hidden by the elytra and other organs for 
flight. — Ex. Coleoptera, Orthoptera, &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. 
