25 



ON THE TRICHOPTEKOUS GENUS POLYCENTROPUS, AND THE 

 ALLIED GENERA. 



BY n. m'lachlax, r.L.s. 



In the present paper it is my intention to offer a few remarks on those 

 insects belonging to the family Hydropsychidce, which agree in possess- 

 ing three spurs on the anterior tibice. Curtis was the first to notice 

 the generic value of this character in the 12th volume of his British 

 Entomology and he was followed by Stephens in the 6th volume of 

 the Mandihulata in his Illustrations, where, in addition to Curtis' genus 

 Polycentropus, two other genera are also described possessing this 

 character, viz. : Flectrocnemia and Cyrims, though in this latter genus he 

 has grouped together some species belonging to widely different genera. 

 In 1857, Brauer, in his useful little work Neuroptera Austriaca, adopts 

 Flectrocnemia. In the Synopsis of the British Phryganidee, published 

 in the Entomologisfs Annuals, Dr. Hagen forms only two genera with 

 this character, viz.: Flectrocnemia and Folycentropus, mio 'Vf\\\c\\\^.9,t 

 genus he merges Gyrnus ; but, for reasons given hereafter, I think it 

 advisable to keep these genera separate; nevertheless, from the confusion 

 that exists in the types in Stephens' collection, it is evident that that 

 author had no very clear idea of the characters laid down in his generic 

 descriptions. In my investigations of these insects I have been much 

 struck with the characters afforded by the neuration, and feel satisfied, 

 that with all propriety, we may give five British genera of Hydropsy- 

 chidce with tricalcarate anterior tibiae. I would remark here that the 

 neuration is not well visible until the hairy clothing on the wings be 

 removed by a camel-hair brush, and that a strong magnifying power is 

 requisite to bring out the transverse veins. I must reserve detailed 

 descriptions of these genera for my work on the British Trichoptera, as 

 they would occupy too much space here ; but have attempted, by short 

 characters, to make my meaning clear. Almost the whole of these 

 insects are of small size, and often very similar in general appearance, 

 many of them having the wings sprinkled with numerous golden yellow 

 spots. They are very active, and some of them run with facility on the 

 surface of the water. The larvae, according to my experience, frequent 

 both standing and running waters. Pictet remarks, that the pupa of 

 his Hydropsyche senex (Fletrocnemia conspersa Curtis) possesses external 

 respiratory filaments, whereas they are wanting in the larva. The case 

 is a heap of small stones loosely put together, and fixed on to some 

 larger stone; these cases are frequently changed. "When the larva is 

 about to change to the pupa state, it constructs a more solid retreat. 



