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body. The circulation (which is not a true circulation, but 

 a simple oscillation of the fluids from one side to the other, 

 first in one direction and then back again,) is regulated by 

 a valve which is not found in the Mollusks, and acts in 

 either direction, according to the motion of the current. 

 Locomotion is produced by the contraction of strong mus- 

 cular bands, whereas in the Mollusks it is generally pro- 

 duced by the alternate contraction of many small muscles. 

 In the Salpa it is difficult to say which is the anterior and 

 which the posterior extremity. On the other hand it resem- 

 bles the Medusae, especially the Bercie, in its transparency ; 

 in the character of its tissue, which is furnished with similar 

 projecting points ; in its stinging power when held in large 

 quantities in the hand ; and in the position of the embryos 

 around the stomach. The Salpa propels itself by taking 

 in water and expelling it again with force by openings, 

 which in the separate individuals are two in number, in the 

 complex chain one for each member. In reply to a ques- 

 tion from Dr. Gould, Mr. Desor said that so far as he had 

 been able to examine it the nervous system is ganglionic, 

 like that of the Mollusks. 



Mr. Desor also exhibited some drawings of a new 

 species of Pelagia obtained by him in Nantucket Bay. 

 This genus has not before been found on this side of the 

 Atlantic; and the species, characterized by having eight 

 eyes, and five long slender threads, he proposes to call P. 

 quinquecm'ha. 



Dr. C. T. Jackson exhibited specimens of a new mineral 

 found in the copper deposit of the Pittsburg and Boston 

 Company's mine at Lake Superior. He had not yet com- 

 pleted its analysis, but it belonged, he said, to the family of 

 the Zeolites. He also exhibited rings ingeniously made of 

 native copper and silver, the two minerals remaining in con- 

 tact just as they occur in the mine. He gave an interesting 

 account of the mining processes carried on at Lake Supe- 



