1914] Forbes—The North American Families of Lepidoptera on 
At the base of the abdomen, on each side, there is a large 
cavity, which, to judge by its position and gross structure, is 
probably auditory in function. This is called the tympanic 
cavity here, and its outlet, which les at the boundary between 
thorax and abdomen, the tympanic opening. Usually it is high 
up, about on the level of the wings in a spread specimen, but 
in the Geometridz it is lower, and generally very conspicuous. 
In the Pericopidze, where it is also particularly large, it is as high 
as in most families, and projects slightly above the general surface 
of the abdomen. 
In counting the number of anals in the fore wing (alternative 
No. 8) an imperfect and rudimentary first anal, which only forms 
a short bar near the margin, is often met; in* the Macros (forms 
with the wing-membrane three or four times as wide as its fringe 
or more, and generally hairy or deep vestiture) such a rudiment 
is not counted; in the Micros (where the wing-membrane is not 
more than twice as wide as its fringe, and the vestiture, except 
on the head, is scaly) it is. Doubtful cases have generally been 
entered twice in the table, but no attempt has been made to make 
the part referring to the Tineina complete. 
Table of Families. 
Tle, WARGO leo ocotc\o. ty are eb A ee CCCI ecient RED Reel Ao ene tea 2 
They WWARIVEIESSS 55 aecs'o GMELIN yet BO SLO enero cet tee ce eee ea 52 
2. Hind wings with four or five radials, with at least ten veins besides anals, wing- 
Mempranegspimlatedep wy spy moe renee ee Ac cise. Stiaic ais ek ale eee 3 
2. Hind wings with only one free radial (two in the otherwise much reduced Doug- 
lasia group); with at most six (or with Sc, 7) veins from cell............. 4 
3. Wings hardly wider than their fringe, expanse about one-half inch 
MicrRopTeRYGID& 
3. Wings ample, fringe narrow, expanse over one inch............. HeEpraLipa 
4. Each wing deeply cleft into six narrow strips.................. ORNEODIDZ 
4, Fore wing moderately cleft into two, and hind wing deeply into three feathers 
PrEROPHORID 
4, Wings entire, or fore wing only, moderately cleft......................... 5 
5. Inner margin of fore wing and costal margin of hind wing narrowly folded, and 
interlocking; fore wing at least four times as long as wide, and base, at least, 
me Glelind awinatrausparente ocr, ii sur. dele. 8 ok co Sie sass wecie t 30s ANGERIID A 
5. Wings not interlocking at middle of margin, very rarely transparent, and if 
Bo wate peaader tonecawan Garter Seen A, ser paene Sones. ss Scala ca ole «+e aceon Sx 6 
1The New England families are indicated by small capitals. 
