1947] 
Banks — Characters in the Perlidae 
273 
is normally five, Paraperla lias but four, Alloperla three, 
and Hastaperla lias no anal area. In most genera the 
second and fifth are branched, in some Acroneuria and 
Perla with several branches. 
In the hind wings the number of cubital cross-veins, if 
more than one, has been used, it varies, but is somewhat 
useful. The number of branches of the second and last 
anal veins, is also helpful, but rarely dependable. The 
length of the union of radial sector and medius has also 
been used, but too variable for a generic character. 
Palpi. 
The palpi in Pteronarcys, Perla, Acroneuria are short 
and inconspicuous, the last joint of the maxillary palpi 
very small, the third somewhat swollen at tip ; in Isogenus , 
the fourth joint is longer, and in some species ( nona , 
ehria, etc.) the palpi are much longer and more slender, 
the fourth joint prominent and the third joint not swollen 
at tip, while in Alloperla the last joint is very short, 
scarcely noticeable. 
Set^. 
The setae, or tails, in the primitive forms (Perla, Acro- 
neuria, Pelto perla) are short and in Perla and Acroneuria 
much thickened at the base and taper to the slender tip. 
The first few joints in Perla are simple annulations, not 
real joints ; in Acroneuria they are usually more like a 
joint, plainly separated by a notch on the side ; in Pelto- 
perla some species are similar to Perla, in others more 
distinct. Also in Perlodes, and Hydroperla some species 
have short setae, the basal joints scarcely separated. But 
in most Perlidae the setae are long, often as long as ab- 
domen, and with many joints much longer than broad, 
and with long erect bristles near tip of each joint. 
Results. 
On considering these characters in the various genera 
one sees that there are two primary trends or groups 
of primitive Perlidae, one the Acroneuria group distin- 
guished by the oblique anal brace arising from near third 
anal vein, the other the Iso genus group with an anal brace 
arising from the base or near base of anal cell and ex- 
