294 Annals Entomological Society of America [Vol. XV, 



widely differ in both species, immaculatus more approaching 

 those hereafter dealt with. In spite of the special form of its 

 mound, the relationship can be traced in the structure of the 

 operculum, the subapical thickening of which is undoubtedly a 

 preliminary stage of the heart-shaped projection of the synoper- 

 culum of impressus. 



Paraiulus impressus Say, 1821, 

 (Fig. 35-42). 



9. Length 33 mm.; diameter 2.20 mm.; 53 segments, of which 2 apodous; 

 96 pairs of legs. — Adult. 



9. Length 26 mm.; diameter L77 mm.; 53 segments, of which 3 apodous; 

 95 pairs of legs. — Immature. 



9. Length 25 mm.; diameter L78 mm.; 53 segments, of which 3 apodous; 

 95 pairs of legs. — Immature. 



Adult Female. — Interocular sulcus slightly depressed. Antennse 

 about the same length as in immaculatus, but comparative measures of 

 joints somewhat different: 



1st joint, length 0. 160 mm.; 



2d joint, length 0.576 mm.; 



3d joint, length 0.512 mm.; diameter ".0.208 mm. 



4th joint, length 0.448 mm.; diameter 208 mm. 



5th joint, length 0.480 mm.; diameter 0.240 mm. 



6th joint, length 0.416 mm.; diameter 0.256 mm. 



7th-8th joint, length 0. 128 mm. 



Total length 2.720 mm. 



Gnathochilarium as in tiganus, but less narrowed proximally (Fig. 

 38); laminae linguales bearing three setas besides the premarginal pair. 

 Mandibular cardo about two-thirds of the stipe ; breadth of mandibular 

 stipe about four-fifths of its length; anterior margin truncate, with 

 lower angle obvious (Fig. 35). 



Second and third segments much swollen (Figs. 35, 36), their ventral 

 surface protruding far beyond the angles of the collum and appearing 

 rounded in profile. Ventral ridge of second segment less sinuous than 

 in the preceding species; dimples as high as broad, almost triangular; 

 the ventral lobes remain disjoined (Fig. 37, A). Third segment growing 

 longer ventrally; inner riiargins almost straight, converging backwards, 

 with rounded anterior angles and short ventral lobes, reflexed and 

 prominent. Ventral aperture wide, filled by the vulvas, which are 

 never completely concealed (except in contracted condition of the 

 anirnal) . 



A rough sketch has already been given in the preceding chapter. 

 The synoperculum sits on a broad base and is narrowed distally, its 

 apical margin being equal to about half its base (Figs. 39, 40). The 

 dwarfed legs of the second pair (P2) are attached to its anterior surface, 

 no sternal plate being recognizable; the legs are composed of six joints 



