1930] 
Geological History of Insects 
29 
percentage dropped to 57%, for Sellards had by then des- 
cribed the Plectoptera, and a few other groups. Now that 
all the Permian orders have been studied, we find the figure 
at 34%, which is probably very close to the correct magni- 
tude. Although we have no previous records to check with 
those of the 1930 columns, it is interesting that the insect 
faunas of the several Permian beds compare very closely, 
although neither the Kansan nor Australian Permian beds 
have been entirely worked out. We are therefore obliged 
to regard the Permian record as more or less temporary 
and probably subject to slight changes when additional 
material has been found. Just how great these changes are 
we cannot say at present. 
TABLE 3. 
RELATIVE ABUNDANCE OF SPECIES IN EACH ORDER AT 
DIFFERENT PERIODS, AS DETERMINED IN 1908, 1920, 1930 
(Figures in Percentages) 
— Permian — — Mesozoic — — Tertiary — 
1908 
1920 
1930 
1908 
1920 
1930 
1908 
1920 
1930 
Mecoptera . 
9.0 
2.0 
3.3 
3.7 
.11 
.13 
.16 
Neuroptera 
3.0 
4.0 
4.1 
4.8 
.60 
.62 
.50 
Odonata . . . 
.80 
6.8 
6.2 
6.6 
1.5 
1.3 
1.6 
Homoptera 
12.5 
4.0 
8.0 
9.0 
4.0 
3.6 
4.0 
Pscoptera . 
6.0 
.15 
.15 
.25 
.40 
.40 
.45 
Coleoptera 
1.0 
35.0 
30.0 
37.0 
40.0 
37.0 
37.0 
Plectoptera 
... 2.8 
7.5 
3.5 
1.8 
1.8 
2.0 
.30 
.20 
.30 
Diptera . . . 
.30 
3.5 
5.0 
5.0 
26.0 
25.0 
27.0 
Orthoptera 
.30 
8.0 
10.0 
9.0 
1.2 
1.2 
1.2 
Blattaria . 
.... 80.0 
57.0 
34.0 
8.0 
7.0 
7.0 
.70 
1.0 
.90 
Leaving the Paleozoic and passing to the later forma- 
tions, we note that at the present reckoning the Mecoptera 
make up about 3.7% of the Mesozoic insects. Although this 
is nearly twice the percentage obtained from the 1908 rec- 
ords, it is still vastly lower than the 9% of the Permian, 
and equally greater than the Tertiary percentage, which 
is quite constant in all of the columns. It seems very prob- 
able therefore that while the relative number of species of 
fossil Mecoptera may vary somewhat as additional beds 
are discovered, these variations will not be sufficient to up- 
set the present trend in the figures, and we are quite safe — - 
