COLEOPTERA. 501 



The parts of the maxilla to which reference is most often made are 

 the palpus and the galea. The number and form of the segments of 

 the palpus are much, used in descriptions ; as is also the presence or 

 absence of the galea. When the galea is developed as-a distinct ap- 

 pendage, the maxilla is said to be bilobed, the galea being termed the 

 outer lobe, and the lacinia, or blade, the inner lobe (Fig. 604). When 

 the galea is not developed so as to appear as an appendage the 

 maxilla is said to have but one lobe. 



Much use is made of the form of the parts of the labium or lower 

 lip in descriptions of beetles. When fully developed the labium con- 

 sists of three principal parts and a pair of appendages. The principal 

 parts are the submentum, the mentum, and the ligula ; the appendages 

 are the labial palpi. The basal part of the labium, the part which is 

 joined to the gula, is the submentuin (Fig. 607, sin). 

 By an unfortunate error this sclerite is almost in- 

 variably described in works on the Coleoptera as the 

 mentum. This fact should be borne in mind by the 

 student when using any of the older books on this 

 subiect. The intermediate portion of the labium is ^^g- 607. — Labium 



•' * , . of Creophzius : sm^ 



the mentwn (Fig. 607, m); and the distal portion submentum; /«, 



1 ,. T rr-i 1' 1 • J i_ ^ mentum; jc, labial 



the ligula. The ligula is a compound organ ; but palpus; g-, giossa, 

 in beetles the sutures between the different sclerites ^' paragiossa. 

 of which it is composed are usually obsolete. Three parts, however, 

 are commonly distinguished, a central part, which is sometimes 

 divided at the tip, th^glossa (Fig. 607,^), and two parts, one on each 

 side of the glossa, iht paraglosscB (Fig. 607, p). The part on each side 

 which bear the palpus is termed, when it is distinct, xhQ.palpiger. 



The Thorax. — Each segment of the thorax is composed of several 

 sclerities. The shape and relative position of these sclerites afford 

 characters which are much used in classification. Figure 608 is a dia- 

 grammatic representation of what is considered the typical arrange- 

 ment of these parts in each of the thoracic segments. Each segment 

 of the thorax is a ring, which is divided into four parts: a dorsal, a 

 ventral, and two lateral. The dorsal part is named the nolutn (no'tum) 

 or tergum (ter'gum) ; each lateral part the pleurum (pleu'rum) ; and 

 the ventral part the sternum (ster'num). 



When the notum or sternum of a particular thoracic segment is to 

 be indicated, it is done by the use of one of the prefixes pro, meso, or 

 meta. In this way are formed the terms pronotum, mesonotum, meta- 

 notum, prosternum, mesosternum and metasternum; which are applied 

 to the nota and sterna of the prothorax, mesothorax, and metathorax 

 respectively. 



