Entomology of tJie Illinois River. 207 



conical whitish fleshy base bearing a reddish brown 

 ■cylindrical joint about four times as long as thick, and 

 filightly curved. At its tip is a small hemispherical 

 whitish joint, and beside this a pair of minute points. 

 The mandibles are broad and usually bluntly toothed 

 on the margins. The maxillse are also broad and thick, 

 their palpi resembling the antennae, having a pale coni- 

 cal base and a chitinous short joint bearing a minute 

 terminal joint. The membranous area of the throat 

 (gular area) is ^-shaped, and the mentum has a slender 

 trifid or many-toothed apex curved up into the mouth 

 and often concealed. 



First four body segments about equal in length, 

 gradually thicker, next six about twice as long, divided 

 by a pseudo-suture near middle into two divisions. The 

 anterior divisions are divided above and below by trans- 

 verse impressed lines into three or four folds; the pos- 

 terior divisions are less distinctly divided into three folds, 

 the middle one of which is usually larger and with a 

 darker transverse ridge, bearing above and below minute 

 black stiff hairs or setse, usually four equidistant ones 

 in a straight line above, and four below, the middle 

 pair further forward than the outer pair. Often a close- 

 set pair of setae appear in place of each seta beneath. 



The last two segments are not double and are about 

 half as long as those preceding. On these segments and 

 on the thorax the pubescence is thicker, and the same 

 setae are present, but more numerous on the thorax. At 

 the apex of the last segment [Fig. 33,36,37,39] beneath 

 is the soft fleshy anal prominence encircled by a fine 

 dark line, variously shaped according to the species, 

 often with long appendages, and used in crawling. Above 

 this tlie posterior side of the last segment is abruptly 

 truncate, bordered by fleshy or horny points, enclos- 

 ing the stigmatal field, in the center of which is a pair 

 of large brown or black round stigmatal plates. 



