isiia.) 85 



The principal differences between the larvse and nymph oi Hydro- 

 psyche and those of Philopofamus and Wormaldia, according to present 

 information, may be tabulated thus: — 



I. Hydropsyche. II. Philopotamus and Wormaldia. 



Larva. Larva. 



Head short ; dark in colour. Head more elongate ; clear reddish or 



orange. 



Labrum more or less chitinous above. Labrum membranous, scarcely chitinous 



at all. 



Thoracic segments all more or less chiti- Only prothorax chitinous, same colour 



nons and darkly coloured. as head. 



Abdomen greyish, or dirty white. Abdomen (with mesothorax and meta- 



thorax) very pale yellow or white. 



Tracheal branchise much developed. No external respiratory appendages. 



Nymph. Nymph. 



Large lateral branchia-like processes Such processes absent. 



present on abdomen. 

 Tracheal branchiis much developed. No external respiratory appendages. 



In all the above, and in other respects, Diplectrona agrees with 

 Section I, rather than with II. For that reason, and taking into con- 

 sideration the absence of ocelli in the imago, I am inclined to think 

 that Diplectrona has more in common with Hydropsyclie than with its 

 present associates, Philopotamus and Wormaldia, and that it should be 

 transferred either to the Section of Hydropsyche, or, perhaps better, 

 to a separate Section immediately following. Assuming the early 

 conditions of Arctopsyche to be more or less similar, by the removal 

 of that genus and Diplectrona, the Section of Philopotamus w^ill be 

 rendered more homogeneous, containing as it will a group of active 

 larvae entirely naked as regards external respiratory filaments. The 

 larvae of Dolophilus, Cyrnus, and Neureclipsis are not known to me, 

 but 1 do not think the first will differ greatly from Philopotamus and 

 Wormaldia, and the last two from Plectrocnemia, Polycentropus, and 

 Holocentropus, larvae of all of which five genera I have seen and 

 determined. 



EXPLANATION OF PLATE I, FIGURES ALL ENLAEQED. 



Larva. 

 1. Mandible from above (left). 2. same (right). 3. Mandible from beneath (right). 

 4. same (left). 



5. Labrum. 



6. Labium and maxilla (retracted). 7. same (asserted), more enlarged. 



8. Anterior leg. 



9. Anal limbs. 



