ii"7-' 253 



is founded on one macroptorous specimen from Hungaiy and two brachy- 

 pterous exami)les from Finland. Since then further specimens, more or 

 less agreeing with the desori])tion of niffrita, have been found in Finland 

 and Sweden. In 1912, lleuter (Ofv. Finsk. Vet. Soc. Forh. liv, 7, 

 l)p. 73-75) gave at length his reasons why he regarded nicjrita (as 

 represented by the brachypterous specimens) and montandoni as merely 

 colour-varieties of aestivalis. In the same year Horvath himself (Ann. 

 Mus. Hung. XX, p. 609) stated that montandoni is inseparable from 

 aestivalis ; he did not even maintain it as a variety. Finally, 

 Montandon, the recognised authority on aquatic Hemiptera, remarked 

 in 1918 (Bull. Ac. Koum. i, p. 220) that he, after examination of a 

 long series of specimens fi'om different countries, had found " tous les 

 passages qui ])ermettent de reunir " montandoni and aestivalis. With 

 these authors 1 .perfectl}^ agree. When Horvath's monograph was 

 published I set about examining my material of the genus. I then 

 possessed only a series of specimens which Fairmaire had sent me with 

 the note that they all were from the Seine, and I found at once that 

 I was unable to name them, as they agreed with aestivalis in the 

 colouring, whei'eas in the female genitalia they corresponded to 

 Horvath's description and figure of montandoni. 



As a matter of fact, neither the slight structural differences nor the 

 coloration can be relied on. Reuter suggested that the single known 

 macropterous specimen of nigrita might represent a distinct species, as 

 the head is a little longer, but compared with its own breadth the head 

 is not longer in the macropterous nigrita than in aestivalis : it is 

 apparently longer because the pronotum is a little shorter in the middle, 

 the median length of the pronotum being somewhat variable. I am 

 therefore convinced that we have but one species in Northern and 

 Central Europe. In northern waters only dark specimens occur. The 

 specimens found in Finland and Sweden are all more or less typical 

 nigrita ; Kolenati and othere have found montandoni -cqXqwyq^ speci- 

 mens in the clear brackish estuary water of the Neva near Petrograd. 

 Why the black pigment only partly develops in many mid-European 

 specimens is still an open question. Montandon {I. c.) argues that the 

 coloration depends on " le degre de purete ou de limpidite des eaux," but 

 Frey-Gessner has stated that almost black specimens {nigrita) and 

 specimens with the ochraceous colour much extended live j)romiscuously 

 together in the little river Aabach in Switzerland. 



Jamsa, Finland. 

 Sept. 9th, 1917. 



