Vol. XXVl] ENTOMOLOGICAL NEWS 59 



Labium with hinge halfway between first and second pairs of legs. 

 Mental setae variable in number, usually four on one side, two on the 

 other. Inner seta of the four reduced to a mere spinule, as in the cor- 

 responding one of the two, while the one next to it may be nearly 

 one-third shorter than the normal. Labium occasionally with four 

 mentals, two of which are reduced in size, especially on one side. 

 Lateral setae six. Lateral lobe with three distinct teeth above the end 

 hook, preceded by three minute teeth between which project two 

 spinules. Femora with dark subapical rings. Tibiae with dark basal 

 ring. Gills lanceolate; widest just beyond the middle, with blunt tips; 

 proximal half of their ventral margins straight and strongly spinulose; 

 the dorsal margin slightly convex, somewhat spinulose; distal margin 

 bearing a few long hairs. Gills hyaline with four or five wide, dark, 

 lacey bands formed by pigment covering the tracheal tubes. 



Dimensions. Body 12-13 mm.; gills 5.5 mm. additional. 



III. THE SUPPOSED DIMORPHIC FEMALE OF ISCTINURA VER- 



TICALIS SAY. 



The dimorphism of the female of various species of Isch- 

 n ura has been generally accepted, two forms having been 

 described as the orange and black females of Ischmira verti- 

 calis Say in the keys of Calvert ('93), Williamson ('oo), and 

 others. According to Williamson, both become prninose, the 

 black female less so than the orange. He also notes that the 

 pruinose orange females are more numerous in the spring than 

 the bright orange or black ones, while the black females are 

 most numerous in the autumn. Since it seemed probable that 

 these three forms might be different stages in coloration due to 

 age, some experiments were undertaken to determine their 

 relationship if possible. The results have proved that there is 

 but one female for Ischmira verticalis Say. 



Apparatus. The banks of Cascadilla Pond are straight 

 and grass-grown. Into one of these banks a cut was made so 

 that about ten inches of water might run into the bay thus 

 formed. A simple cage was built to cover this bay together 

 with a bit of the bank. The framework was made by crossing 

 two pieces of heavy wire to form the diagonals of this rectangu- 

 lar space. The wires were bent at the corners so that when 

 placed firmly in the ground they made a framework ten inches 

 high. Over this support a covering of white mosquito netting 



