128 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



Apex of claspers with only 1 or 2 

 apico-mesal black spines, fig. 477. . 

 arva, p. 132 



12. Tenth tergite heart shaped, the apex 

 pointed, the styles arising near 

 meson; internal structure of eighth 

 sternite not conspicuous, fig. 478.. 



xena, p. 130; unio, p. 129 



Tenth tergite triangular, apex round- 

 ed, the styles arising from lateral 



margin; internal structure of eighth 

 sternite frequently sclerotized and 



conspicuous, figs. 479-484 13 



13. Eighth sternite with apical margin 

 produced into a low, distinct lobe; 

 mesal area of internal structure 

 with spicules, fig. 479. . . tarsalis, p. 130 

 Eighth sternite with apical margin 

 nearly straight or merged with ninth 

 and the boundary between them in- 



ARVA 



Figs. 'i73-477. —Ochrotrichia, male genitalia. J, lateral aspect; C, ventral aspect; D, 

 tenth tergite, dorsal aspect; E, tenth tergite, right side. 



