NOTES AND EXHIBITS. 219 



work on the Mammals of the Indian Archipelago, for comparison 

 with the specimen of a new species of Dendrolagus exhibited by 

 the Hon. Wm. Macleay at the last meeting, (3.) Specimens of 

 the Lizard referred to in his paper. 



Professor Stephens exhibited a pebble from Casino, containing 

 an included drop of water, which did not entirely fill the space in 

 which it was enclosed. The stone was a nodule of chalcedony, evi- 

 dently washed out of a volcanic rock, in a cavity of which it had been 

 formed by infiltration of hydrous silica, the process having been 

 in all probability only arrested by the decomposition of the matrix 

 and consequent liberation of the nodule. The cavity had been 

 first lined by some (probably) zeolitic mineral, forming a mammil- 

 lary surface, which had been subsequently covered by the inner 

 aud harder silicious substance which now enclosed, the drop of 

 water accompanied by some gas. The phenomenon is not at all 

 uncommon, but often escapes notice. 



He also exhibited a Chrysalis of a Danais, secured by a silk line 

 to a leaf of an exotic Pelargonium. 



caS^^S^- 



