OSTEN SACKEN ON WESTERN DIPTERA. lid^ 



JE. dulcis has a striking resemblance to JE. caloptera Say of the Atlantic 

 States. An obvious difference between them lies in the structure of the 

 discal cell, which in U. caloptera is formed by the forking of the anterior, 

 in E. duUis of the posterior, branch of the fourth vein. The distribu- 

 tion of the vf'hite spots on the wings is different in both species, as 

 E. caloptera has many spots inside of the cells, while E. dulcis has none- 

 Besides the brown ring at the tip of the femora, E. caloptera has a second 

 one about the middle. The discal cell here is generally closed, while iu 

 E. caloptera it is more often open. Nevertheless, the homologies between 

 the present species and the group Mesocyphona, to which E. caloptera 

 belongs, are very striking. They consist in the position of the brown 

 thoracic stripes; in the presence of a brown ring on the femora ; as far as 

 I can see, in the structure of the male forceps, which resembles the figure I 

 gave of the forceps ofE. caloptera (1. c, tab. iv, f. 15) ; and the course of the 

 last longitudinal vein, which is undulating, and at the same time diverging 

 from the preceding vein, thus holding the middle between the converg- 

 ing arcuated seventh vein of the subgenus Erioptera and the straight 

 and diverging one of the subgenus Acypliona. 



Thus, E. dulcis would be well placed in the same subdivision with 

 E. caloptera, the subgenus Mesocyphona ; only the definition of the sub- 

 genus should be modified, and less stress laid on the forking of the 

 anterior or posterior branches of the fourth vein. The subdivisions I 

 proposed for the genus Erioptera (Monogr., iv, p. 151) were based mainly 

 on the sixteen North American species which I knew at that time. I 

 believe that in the main they will hold good in a more general applica- 

 tion, only their definitions will have to be modified in some points, and 

 based upon a closer study of the male forceps. 



Erioptera bipartita n. sp. — The prsefurca ends in the second sub- 

 marginal cell ; the anterior branch of the fourth vein is forked, and by 

 means of two cross- veins forms a double discal cell ; wings spotted witii 

 brown along the margin and on the cross-veins and forks. Length 

 3.5-5'"™. 



Male and female. — The wings of this species are exactly like those of 

 my E. graphica of the Atlantic States (Monogr., iv. Tab. i, f. 18) ;. 

 only the stump of a vein, which in that species, as the figure shows, 

 protrudes inside of the discal cell, is prolonged here, so as to reach the 

 anterior branch of the fourth vein, and to form a fork with it. The two 

 cross- veins iu the second and third posterior cells thus inclose two disca 

 cells. The distribution of the brown spots is the same as on the above- 

 quoted figure, with some slight differences : the spot at the root of the 

 prnefarca crosses the subcostal cell and reaches the costa ; that at the 

 end of the first vein is smaller, and stops short before crossing the first 

 submarginal cell ; the seventh vein about its middle has a stump of a 

 vein, projecting into the anal angle, and that is also marked with a 

 brown spot ; the fifth vein is checkered with brown spots ; thorax yel- 

 lowish-gray, with an indistinct double brown stripe in the middle ; hal- 



