158 ^J^^^y- 



Bruton, 23, v, 1892). Both sexes of all the forms are represented in 

 the author's collection. The attitude of the living fly in repose, and 

 its gait in walking, are described in Trans. Ent. Soc. London (1895) 

 p. 491. 



Woodlands, Seaton, Devon. 



ISOPTERTX TORRENTIUM, Pictet, AND I. BURMEISTERI, Pictet ; 

 WITH NOTES ON OTHEE SPECIES OF THE GENUS. 



BT KENNETH J. MORTON, F.E.S. 



While the genus Isopteryx does not present the same difficulties 

 as do some of the other genera of small Perlidce (to wit, Nemoura 

 and Leuctra), there is no doubt some confusion still exists with 

 respect to the minor species. This is especially true regarding I. 

 torrentium, Pict., and J. Burmeisteri, Pict., and, in a less degree, with 

 respect to I. tripunctata, Scop., and I. apicalis, Newman, The 

 primary object of the following notes is to set forth the distinguishing 

 characters of the first-named two species, but it may be useful to 

 allude briefly to the other members of the genus. 



Besides the four above mentioned, there are only two other 

 European species known to me, namely, I. serricornis, Pict., and I. 

 montana, Pict. 



I. serricornis stands quite by itself. One of the largest species, it may be 

 separated at once by its somewhat serrate antennae, large folded portion of hind- 

 wings (the generic name is rather a misnomer, as all the species have a folded 

 portion, although relatively not so large as in the present species), and the prono- 

 tum has in each half a dark bar. 



I. montana is also a large species, probably as large as the preceding on an 

 average, and separable from it by the antennae and the pronotum, which has no bars, 

 but sometimes a fine streak on either side. The head is quite devoid of markings, 

 and the ocelli seem to be relatively closer to one another than they are in the other 

 species. The parts of the J genitalia which are most useful for specific determina- 

 tion consist of a chitinous tooth, which is usually visible dorsalwards between the 

 setse, and which is connected with a plate anterior to itself. In I. montana the 

 tooth is not unlike that of I. Burmeisteri, but it seems to be stronger and shorter 

 on its inner edge (fig. 1). There should be little difiiculty in knowing this large 

 Alpine species, numerous examples of which I have seen from the collections of 

 Mr. McLachlan and Dr. Fr. Eis. 



Coming to the smaller species, I. tripunctata and I. apicalis have 

 sliort setse, and the vertex of the head unmarked. There should be 

 no confusion between them, as even in small pale examples of the 

 former the prothorax should serve to identify them, that part being 



