HYDRELLINA. 149 



II. HYDRELLINA. 



The tribe of Hydrellina is characterized by the hairy eyes, the 

 absence of a spine on the second joint of the antennae, and the 

 absence of long bristles on the upper side of the middle tibial. 

 The eyes in some genera are covered with very short, close hairs ; 

 in other genera these hairs are only scattered, but much longer. 

 Haliday restricts the Hydrellina to the genera Glenanthe, Hydrel- 

 lia, and Atissa. It seems that some other genera, as Philyyria, 

 Hyadina, and Axysta can by no means be separated from the 

 Hydrellina, to which they are much more closely related than to 

 the Ephydrina by their whole organization, and chiefly by the 

 structure of the head. The hairs on the eyes of some species of 

 the three last named genera being very sparingly scattered, and 

 therefore difficult to observe, perhaps it will not be superfluous 

 to remark that in the Hydrellina the eyes are always longer and 

 the fare is narrowest beneath the eyes, whereas in all Ephydrina 

 the eyes are rounder, the horizontal diameter being sometimes even 

 longer than the vertical, so that the antennae stand where the eyes 

 are most approximated, and the face increases much in breadth 

 immediately below them. Moreover, in the Hydrellina the hole 

 of the mouth is never strikingly widened, and the face downwards 

 never projects much, whereas the great width of the oral cavity 

 and the great projection of the inferior part of the face is a most 

 striking character for the Ephydrina, excepting only the genera 

 Pelina and Ochthera. A confusion between the two last named 

 genera with any genus of the Hydrellina is sufficiently prevented 

 by the entire bareness of their eyes. 



The genera of Hydrellina may be arranged as follows: — 



Division 1. Eyes with exceedingly close hair. 



, ( Antennal bristle with a short pubescence. Glenanthe Hal. 



I Antennal bristle pectinated. 2 



2 ( Face convex. Hydrellia Desv. 



\ Face impressed. Atissa Hal. 



Division 2. Eyes with scattered hair. 



Face with bristles on both sides. Phjlygria Slenk. 



Face almost bare. 2 



f Costal vein running to the tip of the fourth longitudinal vein. 



Hyadina Hal. 

 | Costal vein running to the tip of the third longitudinal vein. 



Axysta Hal. 



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