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 nf 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. albolabri?. 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 n. sp. 



Mussel of moderate size, rather oblique, moderately to rather 

 strongly inflated ; beaks slightly posterior, moderately large and 

 prominent, rounded ; scutum and scutelliun slightly marked ; edges 



