164 Fragments of Natural History. 
composed mineral before the blowpipe, would seem to show that 
some of the ingredients of the zeolite have passed away. Shepard 
regards the mineral as decomposed mesotype. 
In breaking some of the masses of quartz found in this collec- 
tion, I was struck with the singular opalescent and waxy appear- 
ance of a fibrous and radiated mineral, which was at first supposed. 
to be stilbite or mesotype, and which forms veins and globular 
knots within the quartz. Its characters before the blowpipe, 
soon satisfied me that it could not be identical with either of these 
Species or with any other of the Kouphone-spars; nor am I ac- 
quainted with any other substance to which it bears any near 
resemblance in its general characters. It may prove to be a new 
species; but the absence of any regular crystalline faces in the spe- 
cimens, compels me, thus far, to rely solely upon other peculiari- 
ties for the determination of its character. Of these, I have drawn 
up a description, which, however, I have thought best not to pub- 
lish, until I am enabled to add the results of an analysis of the 
mineral now being made by my friend, Mr. Hayes, which will be 
in season for the next No. of the American Journal of Science. 
Arr. XXI.—Fragments of Natural History ; by J. P. Kirt _ 
_ Lanp, M. D., Prof, ‘Theo. and Prac. eke Medical cones of 
_ Ohio, Cincinnati. 
“TI write that hack i baci seen. = Baum. 
No. l_— Habits of the Naiades. 
Tue operations conducive to the life, sustenance, and propaga- 
tion of the bivalve mollusca inhabiting fresh waters, are usually 
carried on beneath the mud and sand, at the bebtaptl of either 
deep or rapid streams, beyond the reach of human observation. 
Owing in part to this circumstance, but perhaps more to the fact 
that their testaceous coverings have attracted greater attention 
than the anatomical and physiological characters of the animals, 
their habits are at present very imperfectly understood. 
In Vol. xxvi, p. 117, of this Journal, I advanced the doctrine 
that these animals are androgynous, and not hermaphrodite, as 
ally maintained ; also, that the sex of an individual of 
with certainty by the contour 
