FRESH -WATER MOLLUSKS. 563 



destructibility are desiderata, that it would be idle to attempt to cate- 

 gorize them. 



The invention is being taken up practically on the Continent, and 

 no less in England. Messrs. Powell, of Whitefriars, are introducing 

 it in their glass-works, and two other firms in the north of England 

 are doing the same. It is by no means improbable that its first intro- 

 duction in practice in this country will be at the aquarium now in 

 course of erection at Westminster, where it is intended to use it for 

 the tanks. 



There still remain some questions to be answered with regard to 

 the phenomena exhibited by toughened glass questions, however, 

 which in no way affect the practical value of the material. Its pecu- 

 liarities continue to form the subject of investigation, and, as soon as 

 any conclusions of value to science have been arrived at, they will be 

 made known, so that the physical aspect of toughened glass may again 

 be reverted to in these pages. It only remains to observe that the re- 

 markable character and unique nature of M. de la Bastie's invention 

 are such as to render it probable that lie will not only materially bene- 

 fit those of his own time, but will bequeath to posterity an invaluable 

 legacy. Popular Science Heview. 



4 



FKESH-WATER MOLLUSKS.' 



Br Peof. EDWARD S. MORSE. 



T TNDER lily-pads and on the stems and leaves of other aquatic 



vJ plants, and on stones in rivers, snails of various kinds will be 



found. A dipper with the bottom perforated, or made into a sieve, 



and attached to a wooden handle four or five feet in length, will be 



Fig. 1. Dippeb attached to a Wooden Handle fok collecting Snails. 



found useful in scooping up the sand or mud from the bottom of rivers 



and ditches. The dirt having been sifted out, the shells and other 



' From " First Book of Zoology," now in press of D. Appleton & Co. 



