TiLLYARD.—Stone-flies of New Zealand. 197 
Arr. 18.— The Stone-flies of New Zealand (Order Perlaria), with 
Descriptions of New Genera and Species. 
By R. J. TILLYARD, M.A., Sc.D. (Cantab.), D.Sc. (Sydney), С.М.2.8., 
F.L.&, F.E.S.; Entomologist and Chief of the Biological Department, 
Cawthron Institute, Nelson, N.Z. 
[Read before the Nelson Institute, 19th October, 1921; received by Editor, 26th October, 
1921 ; issued separately, 17th February, 1923.) 
Tue stone-flies, or Perlaria, form a very distinct order of insects, character- 
ized by a combination of a primitive orthopteroid form of imago with an 
‘aquatic hemimetabolous form of larva. e perfect insects may at once be 
recognized by the following principal characters: Head wider than long, 
flattened ; meso- and meta-thorax quite separate and well developed, so 
that the wings are fairly wide apart at their bases; legs with short coxae, 
usually placed wide apart, the femora rather flattened, the tarsi three- 
segmented. Abdomen with ten distinct segments and a pair of anal cerci, 
which ‘may consist of from one to very man segments; no appendix 
always has only two branches), the presence of a series of intercubital cross- 
veins in the forewing, and the position of Cu, just anterior to the cubito-anal 
furrow ; in the hindwing there is always some amount of fusion between 
Rs and M close to the base of the wing, and 1А runs parallel and very 
close to Cus. 
The perfect insects fly but little, and are usually to be found in close 
proximity to the streams in which their larvae live, either resting on rocks 
or hiding amongst the foliage fringing the water’s edge, from which they 
can best be dislodged by sweeping. 
The larvae are in general of a similar shape to the imagines, and are 
usually to be found in those parts of the stream where the water runs 
water. In many cases external gills are developed on different parts of 
the body; the form and position of these 
characters within the order. The larvae are of economic value as trout- 
The order is especially well represented 
rts of New Zealand, and a large number of the new species 
b in i Otago and Southland. These are being studied 
The main object in 
