102 



deposited there; mature shells may have crept into such waters. 

 The Unios lay thousands of eggs, in some species very mature, in 

 others less so. 



In answer to an inquiry from Dr. Jackson whether, from the ascer- 

 tained growth of shells in this manner, it would be possible to deduce 

 the approximative period during which geological strata composed 

 principally of shells had been deposited, Prof. Agassiz replied that he 

 was satisfied that nothing could be obtained from such data ; the ele- 

 ments of the problem were not in them. 



Capt. James Anderson, of the steamer Canada, was elected 

 a corresponding member. 



February 20, 1861. 



The President in the Chair. 



Dr. C. T. Jackson presented, in the name of Mr. Addison 

 Gott of Rockport, Mass., several specimens of rock per- 

 forated by boring animals, from the bottom of the sea, off 

 the Coffin Islands, in twenty fathoms of water. These are 

 part of the Magdalen Islands, in the Bay of St. Lawrence. 

 The thanks of the Society were voted for the donation. 



Prof. Agassiz remarked that the round perforations in this rock 

 were made by the Saxicava rugosa, a bivalve shell. He had found 

 these shells in the perforations, though they have generally been 

 found at the foot of the Devil's apron and other algas. As to the 

 point whether the holes were made by the animals found in them, he 

 thought they were, as they are of the size and shape of the shell ; 

 he did not think they could be produced by any acid secretion ; the 

 hardest rocks and lavas are perforated by sea urchins. He believed 

 they were made by mechanical agency, and probably by the incessant 

 movement of the brushes of vibratile ciha along the edges of the 

 mantle of shells and ambulacral tubes of echinoderms. 



Prof Wyman did not think that the rasps of the Nalica are sufficient 

 to make their perforations in other shells ; they are mere develop- 

 ments of epithelial cells, and do not appear different from the cell 

 walls : the effect looked to him more like that of chemical than me- 

 chanical action, the solvent being the most concentrated where it is 

 used, that is, on the stone, and not necessarily acting on the shell, 

 where it would be greatly reduced. 



Mr. F. H. Storer did not think it difl^cult to admit the secretion of 

 an acid which should act on the rock and not on the shell, in the 

 same manner as the gastric juice acts upon animal matters and not 

 on the coats of the stomach. 



