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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 37 



combs ; its axis is occupied by the "pseudoradula," a rugose band, 

 which is a thickening of the inner surface; in sections, the hypo- 

 chilum appears as a fold enclosing a rather wide cavity communi- 

 cating at the back with that of the head. It is not opposed to the 

 mandibles as is that of the other Chironomidae. There are no 

 maxillary plates. 



Rrm pgl 



Fig. 8. — Macropelopia cf. ncbulosa Mg. 



Dorsal three-quarter view of the labial and hypopharyngeal skeleton, slightly 

 reversed in the stomodeal lumen (which in the figure would take place on the 

 left side). Prm, prementum ("epilabium" or "glossa" auct.) ; pgl, "paraglossal" 

 scale flanking the prementum ; arc d, dorsal arch of the hypopharyngeal skele- 

 ton bearing the double fringe of teeth ; Trao, tendon of the retractor angulorum 

 oris, which is inserted near the toothed fringe ; CS, the single salivary duct ; 

 Pa lab, labial palp. 



A little to the back appears the labiohypopharyngeal complex 

 (s.str.), supported by a rather complicated skeleton (fig. 8). In 

 sagittal sections it appears as a fold of the basal buccal atrium ; in 

 Macropelopia it gives the distinct impression of a unit, for the salivary 

 conduit (the fusion of the two tubes is formed on their entrance in 

 the head) does not widen in the large meatus which in Chironomus 

 deeply separates the hypopharynx from the labium. 



Externally, the labium of this complex has a kind of strongly 

 sclerotized shield, toothed on its anterior extremity (so-called "glossa" 

 or "epilabium" of authors) and bound by a membrane to the hy- 

 pochilan tegumentary fold. At its base the labial or premental muscle 

 is inserted (fig. 13). The homologue of this shield in Chironomus 

 is only lightly indicated by a slight sclerotization. Moreover, dorsally 

 to this premental shield, but a little to the back, the labium is fur- 

 nished with papillae, and more especially, with two lateral palpi form 

 innervated organs. 



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