232 Mr. R. M'Lachlan's Descriptions of the 



XVI. Descriptions of the British Species of the Genus 

 Stenophylax. By R. M'Lachlan, Esq., F.L.S. 



[Read 4th Nov. 1861.] 



The genus Stenophylax of Kolenati consists of insects which, 

 though of considerable size, have from their great similarity in 

 general appearance, been much confused in collections and books. 

 Tiie separation of the species is, however, not very difficult if a 

 careful examination is made of the anal appendages of the males 

 and the characters there presented, coupled with the variations in 

 the form and markings of the wings ; and it may be worth 

 remarking, that in the Phryganidce, where these appendages show 

 any marked differences, there are always other characters by 

 which the species may be separated, although these at first sight 

 may be little apparent. This applies particularly to the appen- 

 dages properly so called, and not so much to the generative organs 

 and sheaths, which are liable to slight variations and are apt to 

 change their form in drying. In this genus two pairs of these 

 appendages are found, the superior and inferior; these are placed 

 on the extremity of the last abdominal segment, but are not 

 attached to its margins ; both pairs are seldom well developed in 

 the same species. Between the superior appendages is an upper 

 pair of sheaths or intermediate appendages; these are usually fine, 

 pointed and divergent. On the underside of the last segment and 

 between the inferior appendages are placed the sheaths proper, 

 which are usually parallel or convergent and between which lies 

 the male organ. In addition well marked characters are some- 

 times found in the form of the upper margin of the last segment. 

 The females are far less easy to separate, especially old specimens 

 with no history attached to them ; they are usually larger than 

 the males. The larvae, according to Pictet, frequent running 

 waters and construct a straight tubular case of small stones neatly 

 agglutinated together, which is fixed to a large stone or other 

 substance at the smaller end. The perfect insects are of nocturnal 

 habits, coming to light and to sugar placed on trees to attract 

 moths, but may be beaten in the daytime from trees in which 

 they take refuge. 



About the earliest reliable descriptions of species in this genus 

 are to be found in a paper by Curtis in the Philosophical Trans- 

 actions for 1834, intituled " On some Nondescript Species of 

 May Flies of Anglers." He there describes four species which 



