No. 459.) WHITE MOUNTAIN RHIZOPODS. 155 
Besides the recording of the species from this general region, 
one further use was made of this material: a comparison was 
made with the average measurements of Leidy. The results of 
this comparison may best be seen in the following table : — 
Leidy-Average. 
Aper- per- Aper- 
Lgth. Bdth. ture. Lgth. Bdth. ture. Lgth. Bdth. ture. 
Difflugia constricta. 
Intervale 178 117 49 Mt. Munroe 68 37 15 320 no 68 
Nebela collaris. 
Squam Lake 102 75 37 Lakeofthe Clouds 80 59 22 161 135 — 
Arcella mitrata. 
North Conway — .155 63 Lake of the Clouds — 7 34 = 142 56 
Centropyxis ecornis. 
North Woodstock — 83 34 Mt. Munroe — 59 28 — 146 64 
From the above table, which represents the conditions seen 
in almost all the species under observation, the difference in 
size between the average measurements of Leidy for the whole 
of North America and the average measurements for this region 
is at once apparent. That this is due rather to latitude than 
altitude it seems safe to infer as the valley lakes are no higher 
than many of the medium records of Leidy. If it is safe to 
draw a conclusion from this, it at least seems to indicate that 
these animals are as a rule smaller in higher latitudes than in 
lower. Such a conclusion, of course, cannot be of great weight 
unless worked out in other cases, but is at least indicated here. 
The other point which seems much more certain by direct 
comparisons in this same general locality is that some species 
are smaller on the tops of the mountains than they are in the 
valleys of the same region. In the first column are given the 
measurements of typical valley specimens and in the second 
column the measurements of specimens of the same species 
from lakes of about 5000 feet altitude. The differences in this 
case are at once marked and definite and it may be said with 
every degree of certainty for the species here worked out that a 
species at high altitudes will be smaller than the same species 
in lower altitudes of the same region. This one fact seems to 
repay the time spent in working up the various lots of material. 
