PROC. ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 55 



Snodgrass, 1909, refers to the plate en of figures 18, 19, 21, 

 etc., as the "notum," in the restricted sense; but the term 

 notum has always been used as a synonym of tergum, and refers 

 to the entire dorsal region (both membrane and the more heavily 

 chitinized sclerites) of the segment. On this account, the term 

 "scutoscutellum" was applied to the plate in front of the post- 

 scutellum (Crampton, 1914, Martin, 1916, etc.) but since this 

 term is somewhat cumbersome, the simple designation eunotum, 

 which has been suggested for the plate in question, has been 

 here adopted. 



In the young of certain of the more primitive insects, a mar- 

 ginal region extends entirely around the eunotum, as in the pro- 

 notal region of the nymph of Perla (fig. 24, per}. In the meso- 

 notum of the Carabicl larva shown in figure 21, this marginal 

 region is incomplete, only the anterior portion prt having been 

 retained, although this region extends backward for a short dis- 

 tance along the sides of. the plate. In the mesonotum of the 

 nymph of Perla (fig. 15) the anterior transverse region prt, and 

 in the pronotum of the Trichopteron larva shown in figure 19, 

 the posterior transverse region pot, are all that remain of the mar- 

 ginal region per of figure 24. The anterior transverse marginal 

 region /;// of figures 15, 18, etc., is apparently homologous with 

 the preterbite of adult insects, and the posterior transverse mar- 

 ginal region pot of figure 19 is apparently homologous with the 

 postergite of adult insects. The anterior region prt of figure 15, 

 occurs in many Lepismids and other Apterygotan insects, as well 

 as in the pronotum of many Pterygotan forms, such as the 

 Grylloblattids, Embiids, etc. (see figures by Crampton, 1917 b), 

 and may therefore represent the primitive condition, rather than 

 the remains of a marginal region originally extending completely 

 around the normal plate. The region prt (fig. 15, 18, 21, etc.) 

 does not represent the prescutum, but is formed in front of the 

 latter region; similarly, the region pot of fig. 19, does not repre- 

 sent the postscutcllum, which is formed behind the latter region. 

 In the mesonotum of the Coleopterous larva shown in figure 

 22, there occur three regions psc, sc, and psl, which are demarked 

 by wrinklings of the integument. The region psc apparently 

 represents the true jtrcxcutum, while the region .sc corresponds 

 in a general way to the scutum of the adult. Concerning the 

 region psl, there is some doubt. That it contains the postscutellar 

 region is quite certain, but the true postscutellum is extremely 

 small in the mesothoracic region of Coleoptera in general, thus 

 suggesting that the region psl of figure 22 may possibly contain a 

 portion of the scutellum also. 



An examination of the sclerites of Apterygotan insects would 

 indicate that the condition shown in figures 24, 21, and 18, more 



