AMERICAN DIPTERA. 183 



the latter that represented by fig. 6. Hence there were here con- 

 fused two decidedly distinct species. 



The objection to using hypopygial characters in specific descrip- 

 tions is that the characters are hard to get at, and that their study 

 involves the mutilation of specimens. When studying a dried speci- 

 men, one must break off the end of the abdomen, boil it in water 

 until soft, and then dissect under a simple microscope and examine 

 some parts under a compound microscope. Drawings must be made 

 of all the parts, for differences are often such that descriptions alone 

 would be inadequate. Here another difficulty arises, for the same 

 parts often have very different appearances when placed in but 

 slightly different positions. Yet the specific differences are in these 

 parts so strongly and definitely marked that their study would cer- 

 tainly repay the expenditure of a great deal of time and patience. 

 A specimen having the end of the abdomen broken off is worth just 

 as much as an unmutilated specimen, which, by its very perfection, 

 forbids the student any knowledge of its structure. If drawings 

 and descriptions are made of the removed parts, then the mutilated 

 specimen has certainly done more for science than the perfect one 

 ever can do. 



Genus ANTOCH4. 



The structure of the hypopygium is undoubtedly more primitive 

 in this genus than in any other examined by the writer. Other 

 genera, such as Rhamphidia and Dicranoptycha of the group Lim- 

 nobina Anomala, which is Osten Sacken's Section II of the Tipuli- 

 dse, do not show this simplicity of structure. The hypopygium of 

 Antocha is even more simple than in the genera of Osten Sacken's 

 Section I — the Limnobina; hence it is here described first. 



Antocha opalizans O. S. (PI. VIII, figs. 5, 8. 11). 



Abdomen slender, hypopygium scarcely forming an enlargement. 

 Eighth segment very simple ; tergum and sternum subequal, form- 

 ing a simple ring widest on the middle of the sides (fig. 5, viii). 



The hypopygium is of primitive form, consisting of a tergal plate 

 above, a sternal plate below, and of a large pleural plate on each 

 side between the tergum and sternum (fig. 5, ix, t, p, s). The pos- 

 terior face of the segment is deeply concave, forming a cup-shaped 

 cavity, the genital chamber. In it are situated the penis and its 

 guard, the gonapophyses, and the rudimentary tenth segment. 



TKANS. AM. ENT. 80C. XXX. JUNE. 1904. 



