1805.] 107 



8IALIS FULIGIN08A, PICTET ; A SPECIES NEW TO BRITAIN. 

 BY B. m'lACHLAN, F.L.S. 



In the beginning of June, I obtained at Camachgouran, Loch 

 Rannoch, specimens of a Sialis, which I have identified with S.fuligi- 

 nosa, Pictet, Brauer ; thus we now possess both the European species 

 of the genus. 



It differs from the well-known and abundant S. hdaria'nx the much 

 darker colouration of the membrane of the wings, which is most evident 

 at the base ; the neuration and the body also partake of this intensity, 

 the latter being deep black, whereas in lutaria it may be called dark 

 fuscous-black. The existence of structural specific characters in the 

 arrangement of the nervures is perhaps doubtful, as no two specimens 

 of either species agree precisely in this respect, and very frequently 

 the right and left hand wings of the same individual present wide dif- 

 ferences in the number of the apical forks, and of the transverse veins, 

 and the positions of these latter ; nevertheless, there is one character, 

 deduced from the comparison of a large number of specimens of lutaria, 

 and about a dozen oifuliginosa, which is apparently constant ; I allude 

 to the position of the small transverse vein placed between the sub- 

 costa and the radius, and marked a in the accompanying figures. In 

 a fuliginosa this vein is placed opposite 



/^"^ ^^^5^^2j\. *^ about the middle of the cell below 



j^ g ^^^^^^^^^^ ^^» sometimes rather nearer the apex. 



1 In lutaria the vein is placed much nearer 



^^_^^^^^^" -- the base, often almost at the point of 



/ I ^^^^^^^^^ furcation of the two veins forming the 



2 g ^-'CcZ^^^^ upper and lower sides of the cell, never 



approaching the middle. In insects in 



which the neuration is so very liable to vary, as in these two species, 



this character may pei4iaps be of little importance, but as far as I see 



at present, it seems trustworthy. 



Other far more important characters exist in the abdominal appen- 

 dices, but these are nearly lost in dry specimens, and as I neglected to 

 place any in alcohol, I cannot now describe them fully. The form of 

 the valve or lobe proceeding from the ventral surface of the penultimate 

 segment of the male is widely different, and can be distinctly seen even 

 in cabinet specimens. In fuliginosa this lobe is much smaller than in 

 lutaria, shorter and sub-triangular, whereas in lutaria it is very large, 

 the sides nearly parallel, and obtusely rounded at the apex, reacliijig 

 almost to the extremity of the last segment. In both species this lobe 



