164 Fragments of Natural History. 



composed mineral before the blowpipe, would seem to show that 

 some of the ingredients of the zeoHte 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 Konphone-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, 1 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'. 



Art. XXI. — Fragments of Natural History ; hy J. P. Kirt- 

 LAND, M. D., Prof. Theo. and Prac. Phys., Medical College of 

 Ohio, Cincinnati. 



"I write that which I have seen." — Le Baum. 



No. I. — Habits of the Naiades. 



The 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 bottom 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 

 was usually maintained ; also, that the sex of an individual of 

 many of the species is indicated with certainty by the contour of 

 the shell. 



