10 THE AMERICAN MIDLAND NATURALIST 
Day Marks or other improvements along the river, ravines, 
elevation of adjacent hills, clumps of bushes, trestles, ete. 
The first 2 types of reference points were not used when any- 
thing better could be observed. The light list referred to 
gives the distances of these markers and lights from more 
accurately defined points such as bridges, etc. Ass data furnish- 
ed by local clammers was sometimes found to be misleading, 
positions of productive shell beds were frequently determined 
by a trial drag with a single bar at varying distances from 
the shore, when, after encouraging results, the three con- 
secutive drags with both bars were attempted. All beds of 
shells of fair extent which the party encountered are also 
indicated upon the maps mentioned. 
Once the reference point was established, the distance 
across the water of the starting point of the drag from this 
was estimated independently by the three members of the 
party. The average taken of these distances is that one given 
in the descriptive material of the localities, and in case of 
great varieties in estimate, the more probable distance was 
verified by measurement of other points on the map within 
sight, and by the making of comparisons. A map case of the 
type used in the U. S. Army, -provided with compass and 
transparent waterproof cover was found to be a convenient 
carrier for the maps in the field, where the localities could © 
be promptly indicated. A leather-bound notebook of the type 
used by engineers was found to be serviceably adaptable for 
the recording of data. It should be borne in mind, however, 
that as the larger portion of the work was accomplished under 
conditions of high water, it was difficult to accurately estimate 
the position of the normal shore line, and the distances given 
are those of the position of the outfit from the nearest land 
above water at the time. 
V. LIST OF SPECIES COLLECTED. 
The following list embraces those species of mussels col- 
lected within the areas surveyed. Besides indicating the 
common name by which the mussels are known to clammers, 
the older scientific names of Simpson’s Descriptive Catalogue 
of the Naiades are given, and their equivalent in the forth-— 
