It probably first came over with some merchandise which was shipped 

 west by the Erie Canal. The snail, once established in the canal, has 

 had every opportunity to spread over the entire United States. The 

 canal is emptied every year and cleaned, and the water with its organ- 

 isms is allowed to flow into the little streams and the larger rivers 

 and thence into Lake Ontario. From this lake, the species has spread 

 so that it is now found in Lakes Erie and Michigan, and it will even- 

 tually spread over the entire northern portion of the United States. 

 This is but one of the many examples of different species being carried 

 by human agencies from one part of the world to another. 



" But there are many species of these smaller fresh-water snails 

 that are pigmies indeed, whose tiny shells do not exceed an eighth 

 of an inch in length, and which require the aid of a microscope to ade- 

 quately study their delicate organism. These minute organisms live 

 on water-plants and on any submerged object. They vary from long, 

 pointed, steeple-like shells to those which are perfectly round, like 

 a miniature apple. These little creatures are found in all parts of the 

 world, and in our own country they may be found in any of our 

 ponds and streams. The lively little animals are 

 well worth a closer acquaintance. They are known 

 scientifically under the rather difficult names of Palu- 

 dinella, Amnicola, Somatogyrus, Fluminicola, Poma- 

 tiopsis, and many others, and do not have any specific 

 English titles. 



" There is another group of mollusks which is inter- Pomatiopsis l a p i- 



, , ,, , daria, a minute fresh- 



mediate between the land shells and the iresn-water wa ter snail. Animal 



shells,' ' continued the Professor, and you will observe ! ' enlar ed - 



several good specimens in this case. One of these 

 belongs to the family Amphibolidce and has a spiral shell. It inhabits 

 the seashore salt marshes of New Zealand, where it lives in pools 

 of brackish water. During dry periods it buries itself in the sandy 

 mud. The aperture of this shell is closed by an operculum, and the 

 branchial cavity communicates with the air by a valvular opening. It is 

 said to be esteemed by the natives of New Zealand, as an article of food. 



" Another example of this curious group is the Siphonaria, which 

 lives on the seashore, between tides. The shell is flat like that of the 

 limpet, and the single genus Siphonaria is found in most parts of the 

 world." 



Having spent nearly the whole afternoon in the museum, we returned 

 home, filled with enthusiasm, and each one determined to acquire a large 

 and fine collection of shells. 



23 



