304 Mr. R. McLaclilan on 



RHYACOPHILID^. 



Genus Rhyacophila. 



Though most of the numerous species of this genus 

 (restricting it to those in which the dorsal margin of the 

 last segment is prolonged in the middle) resemble each 

 other greatly in general appearance, they possess most 

 satisfactory characters in the appendices of the cj ; the 

 ? on the contrary can, in many cases, only be properly 

 paired by observing the insects in their native haunts. 



Without entering into lengthy descriptions, I propose, 

 with the aid of figures, to notice the distinctive characters 

 of several of the closely allied species, in amplification of 

 Hagen's synopsis in the Stettin Zeitung for 1859, pp. 

 153, 154. 



B. torrentium, Pictet, is so different from the others 

 both in size, colour, and the formation of the lobe and 

 appendices, as to prevent the possibility of mistake — 

 Vide Brauer, Neurop. Aust. fig. 21. 



R. dorsalis, Curtis, and B. vulgaris, Pictet. In general 

 appearance, in the app. inf., and in the form of the dorsal 

 lobe of the last segment these two species agree remark- 

 ably ; the lobe is perhaps rather less dilated at the extremity 

 in vulgaris. The principal difference, as noted by Hagen, 

 consists in the form of the penis, which, in dorsalis is 

 simple with (ordinarily, but not always) downward- 

 directed spine-like sheaths (PL XIY. fig. 13) , whereas in 

 vulgaris it bears a blunt sub-triangular projection on its 

 under side about the middle, with up-directed sheaths 

 (PI. XIV. fig. 12) . The figure of the appendices of dor- 

 salis in my " Trichoptera Britannica " is incomplete, the 

 engraver having omitted the app. sup. The type of vul- 

 garis sent to Curtis by Pictet, does not show the form of 

 the penis very distinctly. 



B. -panpera, Hagen, differs from the above two species 

 in its darker coloration, in the dorsal lobe, which is not 

 dilated at the end and is shorter than the app. sup., 

 and in the straight penis-sheath (PL XIV. fig. 14) . 



B. fasciata, Hagen, may be distinguished almost with 

 certainty by the dark fasciae on the anterior wings. The 

 form of the dorsal lobe is very distinct from the preced- 

 ing, being broad and rounded, and nearly concealing the 

 app. sup. The second joint of the app. inf. is obliquely 

 truncate (PL XIV. fig. 16). I have three cJ from Carin- 

 thia from Zeller, 



