

COMPAEISON OF AGABTTS AFFINIS WITH A. UNGUICULARIS. 273 



A comparison of Agabus affinis, Payk., with unguicularis, Thorns. 



(irith tiro plates). 



By FRANK BALFOUR-BEOWNE, M.A. (Oxon), F.R.S.E., F.Z.S., Director 

 of the Sutton Broad Laboratory. 



In the E7it. Mo. Mag., v., 17, 1868-9, Dr. David Sharp published 

 a note upon Ai/abus affinis, Payk., which, up to that time, had been 

 confused in British collections with Agabus unguicularis, Thorns. 



He gave the following characters, partly from Paykull and Thomson 

 and partly from his own observation, for distinguishing the two 

 species : — 



1. The more parallel form of affinis. 



2. The large punctures on the elytra being more evident towards the base in 

 affinis than in unguicularis. 



3. The difference in shape of the laciniffi of the metasternam in the two species. 



4. The reflexed margin of the base of the elytra being quite black in affin is 

 and obscure red in unguieuUms. 



5. The darker and blacker general colour oE alfinis as compared with the more 

 brassy black of unguicularis. 



In 1904, Mr. W. E. Sharp contributed a note to the E7it. Rec, 

 xvi., pp. 90-92, in which he sought to make the distinctions between 

 these two species clearer. This note was followed by one from 

 Mr. James Edwards, Ibid, p. 187, who suggested that Mr. Sharp had 

 inadvertently transposed the names, as the descriptions did not agree 

 with his knowledge of the species, and he also pointed out that 

 Mr. Sharp had undoubtedly made a mistake in referring to Mr. 

 Thouless' comparison of the stridulating files of the males of the two 

 species. This note drew a non-committal reply from Mr. Sharp and 

 there the matter dropped, leaving the separation of the two species 

 more difficult than it was before. 



I have had the opportunity of collecting both species in Britain, in 

 fair numbers, and, in view of the contradictory statements in the notes 

 already referred to, I have thought it worth while to examine the two 

 species carefully, with a view to making a clear statement as to their 

 character. 



Agabus unguicularis, Thoms., is a species which occurs not 

 uncommonly in East Norfolk, and I have also recently taken a number 

 of specimens at Chaloner's Whin, York, which agree in their 

 characters with my Norfolk specimens. 



Agabus affinis, Payk., is, I venture to think, a not uncommon 

 species in the south of Scotland — I have done very little collecting in 

 the north — and I believe Professor Hudson Beare is of the same 

 opinion. I have taken it fairly commonly in Dumfriesshire, Kirk- 

 cudbrightshire, and Dumbartonshire, the only three counties in which 

 I have done any extensive collecting, and I have examined more than 

 40 specimens of each of these species before venturing on this note. 



Mr. W. E. Sharp took as his type of affinis certain specimens sent 

 to him from Sweden. They were females, and he found, on comparing 

 them with Dumfries specimens of this species, that "the shape of the 

 latter is distinctly more elongated and parallel-sided, legs and antennae 

 clear red instead of somewhat infuscate, and occipital spots much 

 more distinct and of a brighter colour." 



Now Mr. Sharp admits that he finds the females of the two species 

 "exceedingly difficult to separate," and he omits two points of 

 November 16th, 1906. 



