INTRODUCTIOX. xx'l 



sutures. Tlie prosteriuim is sometimes prolonged in front foruiing 

 a lobe which more or less coitceals the mouth below wheu the head 

 is in repose, as in many Elateridffi and Histeridae ; this is called 

 the prostei'nal lobe. The posterior portion of the prosternuni 

 is variable in form, it is sometimes prolonged in a spine whicli 

 extends deeply into the mesosternum jjis in Elateridse. In many 

 Rhynchophora the prosternuni is deeply grooved at the middle 

 for the reception of the rostrum in repose. 



The cavities in which are inserted the anterior legs are called 

 anterior coxal cavities, and are either entire when they are in- 

 closed behind by the junction of the prosternuni and epimera, or 

 by the meeting of the epimera as in Rhynchophora, or open when 

 a space is left protected only by membrane ; they are separate 

 when the prosternnm extends between them, or conjluent when 

 the prosternnm is not visible between them. 



The second thoracic segment is called the mesothorax, and in 

 Coleoptera is very closely united with the third segment or meta- 

 thorax, which is also closely connected with the abdomen ; these 

 parts together form the trunk or main body of the insect. 



These two segments support on the inferior surface the middle 

 and hind legs, and at the sides of the dorsal surface the elytra 

 and wings. 



The dorsal surfaces of these two thoracic segments are covered 

 by the elytra, and, consequently, invisible without dissection ; 

 they are called inesonotum and metanotum, and consist each of 

 four pieces separated by sutures, and named, commencing with 

 the anterior one of each segment, proscutum, scxduni, scutellum, 

 and post-scutellum. No use has yet been made of them in classi- 

 lication, except that the small triangular piece, usually visible 

 between the elytra at their base, is mentioned under the name 

 scutellian. 



The under surfaces consist of the same pieces as the prothorax, 

 viz.: respectively, weso.si<?rnMm, with its epimera and episterna, 

 and the metaMerniim with the same; these pieces are usually 

 distinct, except that the two of each segment are often united 



Fig. 5. — Under side of Eusattxts erosu/i, .showing the true epipleura, Ep. 



Fig. 6 —Under side of Onemidotus, showing the large coxal plates, PL 



Fig. 7.— Under side of prothorax of Rhynchophorus, showing the closun? of thi- coxal 

 cavities by the epimera. 



Note.— The numbered details on the last six figures refer to corresponding parts 

 on Fig. 1. 



