259 



Cambi'idge, are ei-oded, whilst those in a stream near the pond 

 are unaffected except in certain portions of it where there is 

 a clay bottom. In the Middlesex Canal they are free from ero- 

 sions, but in Concord River the opposite is the case. 



Dr. Weinland said that the observation ©f Mr. Whittemore 

 sustained his view of the question. The worms which infest the 

 shells do not live in sandy bottoms, and he had generally noticed 

 the erosion of the shells to extend just so far only as they are im- 

 bedded in the clay. 



Mr. C. J. Sprague called attention to the fact that the corroded 

 surfaces are in some instances covered with epidermis, which 

 may have been a new growth from the neighborhood of the 

 hinge. 



Dr. Jackson said that he had frequently seen the animal taken 

 out of the shell by the mink or musk-rat, the sun having previously 

 killed the animal and expanded the shell. 



Mr. Whittemore said that the common belief, that the musk-rat 

 brings out the mollusk from the water, and leaves it upon the 

 shore in the heat of the sun for this object, is probably true. 



Mr. F. H. Storer exhibited crystals of Sulphide of 

 Lead obtained by sublimation; one of the accidental pro- 

 ducts of a smelting furnace in Germany. 



He remarked upon the exceedingly great volatility of this 

 compound of lead, and upon the influence which its presence in 

 the atmosphere, even at a great distance from the furnace, exerts 

 upon the vegetation of the region. It has been shown by analysis 

 that large spruce trees, six or eight inches in diameter, contain 

 lead, even in their innermost parts, which had evidently been 

 taken up by the roots. 



Dr. C. T. Jackson gave an account of the Sand-Sharks 

 which are caught near Nantucket. While upon the 

 island recently, he had seen some brought to the shore 

 eight or nine feet in length. From the liver is extracted 

 on an average a gallon of oil, which is used by curriers, 

 and worth seventy-five cents a gallon. The body is used 

 for manure. 



