64 THE NAUTILUS. 
Its favorite location is between the bark and wood of a decaying 
log or stump, and it always selects a cool, shady and rather moist 
spot. It prefers maple, elm or ash. I have never found it in con- 
nection with any of the resinous varieties of wood. 
Now, different kinds of wood in decaying, form products of vary- 
ing shades of color. Thus decayed maple is almost black ; elm is 
dark brown; ash is light brown; beech is still lighter, and birch has 
a reddish tinge. It is no less true that the shells of the H. alternata 
differ in shade and resemble that of the wood in which they are 
found, and which forms a part of their food. Thus those found in 
maple are almost black ; those in elm are dark brown; those in ash 
are light brown; those in beech are still lighter, and those in birch 
have a reddish tinge. I have shells in my collection extending 
through almost every gradation of color, from black to ashy-white. 
In some the black stripes predominate and almost obliterate the 
white ones. In others the black stripes are almost wholly wanting, 
and in a few they are replaced by reddish colored stripes, indicating 
in every case the nature of the hiding-place of each individual. 
Again, the bark of decaying trees clings much more tightly under 
some conditions than under others, and this has a marked effect 
upon the upper surface of the shell. I have one shell which is al- 
most as convex as the H. albolabris. I recollect that it was found in 
a cavity where its upper surface could never be touched. Another 
was found in a narrow crevice, where it had barely room to squeeze 
itself, and its upper surface is perfectly flat, and it might well be 
taken for a subspecies. Between these extremes every variation of 
angle may be found, all seeming to result from a greater or less de- 
gree of pressure. Or, rather, having been governed by the height 
of the crevice in which they developed. 
Theoretically, the supposition may have one or two slight objec- 
tions which it is not necessary to mention, but it is based upon 
several hundred observations, and I believe it to be correct. 
TWO NEW PISIDIA. 
BY DR. V. STERKI. 
Pisidium pauperculum np. sp. 
Mussel of moderate size, rather Piligue, moderately to rather 
strongly inflated; beaks slightly posterior, moderately large and 
prominent, rounded ; scutum and scutellum slightly marked ; edges 
