0. L. Walton 
261 
in the upper third although it had been roughly scraped out. During 
March truncatula became very scarce and the only cause for this that 
I could discover was the presence in the fields adjoining of a flock of 
Lapwings, which are stated in the Leaflet, No. 44, of the Board of Agri¬ 
culture to feed upon this snail. A few survived however. During 
March a considerable number of peregra appeared in the pond, and by 
May 1st, several of these had crawled some ten yards up the streamlet. 
The weather continued wet and by June 14th peregra had reached the 
top of the streamlet; a progress of about two yards per day. During 
July the stream again dried up. Shelford 1 mentions some interesting 
facts regarding the upward migrations of some American mollusca 
from which he concluded that “there is no reason to assume that the 
migration began before the spring floods. If this is true the snails 
could make their way toward the headwaters at the rate of at least a 
mile per year if introduced into a large stream. This must be a response 
to both water pressure and current. The opportunity to secure such 
data is small.” 
Roadside Distribution and its Economic Effects. 
A very large proportion of the localities discovered to be inhabited 
by L. truncatula within the Area examined are roadside ditches and 
streams. Hundreds of likely places were examined in fields, upon hill¬ 
sides, etc., etc., all over the Area, but it was comparatively seldom that 
L. truncatula could be found in such spots. Such places are frequently 
difficult to observe owing to the amount of vegetation, and young forms 
might easily be overlooked; nevertheless I am convinced that the 
preponderance of roadside localities noted is genuine and due to their 
particular suitability. I decided to pay special attention to a series 
of these road sides, and some 50 such spots were visited regularly, and 
samples of snails examined for infection, growth rate, etc. 
The reasons for selecting these places were numerous: 
1. They are more readily visited than many of the others. 
2. They are for the most part distributed in groups in various 
parts of the Area and at different elevations. 
3. They are subject in far greater degree to temperature changes, 
droughts, etc., and have thus served to bring out and illustrate many 
facts regarding infection, breeding habits, and bionomical details. 
1 Shelford, V. E. (1913), Animal Communities in Temjrerate America, p. 106. Chicago 
University Press. 
