THE CANADIAN ENTOMOLOGIST 35 



A NEW CLASSIFICATION OF THE ORDER PERLARIA. 



BY R. J. TILLYARD, M. A. 



Sc. D. (Cantab.) D. Sc. (Sydney), F. L. S., F. E. S., Chief of the Biological Department, 

 Cawthron Institute of Scientific Research, Nelson, New Zealand. 



For some years past I have been studying the Perlaria of Australia and 

 New Zealand, about which little has been made known up to the present. Taken 

 in connection with the forms already described from Southern Chile, Patagonia, 

 Tierra del Fuego and the Subantartic Islands, these insects form a very distinct 

 Notogsean Fauna, clearly marked off from the Perlaria of the Northern Hemis- 

 phere and of the Tropics by the fact that it is made up almost entirely of very 

 archaic types. No representatives of the highly specialized Perlidae (including 

 Perlodida?) occur in these regions; no Pteronarcidse, in the strict sense in which 

 that family will be defined in this paper; no Capniida% Taeniopterygidae or 

 Leuctridaj; and only one or two isolated forms of Nemouridsc (genus Udamocercia 

 of Enderlein). 



In attempting to classify the known Notogsean forms of Perlaria, I have 

 had recourse not only to all available imaginal characters, but also to as care- 

 ful a study of the individual life-histories as the rareness of most of the forms 

 would permit. I am now able to state that, as regards Australian and New 

 Zealand forms, the classification adopted by me, on imaginal characters only, 

 has been fully tested in the case of the corresponding larvae, with the result 

 that these latter are found to group themselves into distinct families as readily 

 as do the imagines, so that the two sets of characters taken together form a most 

 useful and easily understood classification. 



The most archaic forms of Perlaria extant are to be found in the genus 

 Eusthenia and its allies. These have no close relationship with the Pteronarcidae 

 as defined in this paper, the latter being specialized by the reduction of the 

 mandibles, the approximation of the coxae of the forelegs, by the loss of the 

 primitive paired abdominal appendages on segments 1-6, (secondary gill-tufts 

 on the thorax and base of abdomen are developed in some genera), as well as 

 by loss of the original palaeodictyopterous mesh-work or archedictyon in the 

 anal area of the hindwing, and by the presence of a distinct break in the contour 

 of the outer margin of the hindwing, at the distal end of Cuo, where the anal 

 fan leaves the rest of the wing. Thus the only primitive characters left to the 

 Pteronarcidae in common with the Eustheniidae proper are the form of the 

 tarsal joints, the visible clypeus and labrum and the presence of numerous 

 cross-veins in the distal portions of the forewing. In contrast with this, all 

 the true Eustheniidae have a primitive larval form possessing five or six pairs 

 of lateral abdominal appendages functioning as gills, on the first five or six 

 segments of the abdomen, but no secondary gill-tufts at all. These primitive 

 paired gills are closely similar to those found in the larvae of certain archaic 

 Calopterygidae in the Order Odonata. They are carried over into the imago at 

 metamorphosis, as are the secondary gill-tufts of Pteronarcys, but quickly 

 shrivel up. In the imaginal stage, true Eustheniidae possess an altogether 

 complete set of archaic characters, as follows: In the forewing, a complete 

 archedictyon or cross-venation in all parts of the wing, a complete set of cross- 

 veins between Cu2 and lA, a radial sector with three or more branches, a first 



February. 1921 



