Shell of Pleu- 

 rocera elevatuni, a 

 water - breather. 

 (Tryon.) 



Leading the way to a little point of land which extended into the 

 lake, he bade all take off shoes and stockings, roll up trousers, and 

 wade into the water in search of snails. Harry as usual was the fortu- 

 nate one, and soon came across a colony of long, slender shells. " They 

 are a species of the water-breathers," said the Professor, 

 "which are called Pleurocera elevatuni. They are named 

 water-breathers because the oxygen is supplied to the 

 blood by means of a gill instead of a lung, as in the 

 snails which have been previously seen. This snail," 

 he added, " like others of its family, does not like a 

 muddy bottom, but prefers a rocky or sandy bed, in 

 which it delights to partly bury itself. It is seldom 

 found in a muddy pond or stream." 



The animal had a short, thick, wide foot, and its color was blackish 

 or yellowish in a more or less mottled pattern. The head ended in a 

 rather long rostrum, or snout, which was yellowish with a black patch on 

 top, and the mouth was placed at the extreme tip. The tentacles were 

 long and tapering, and the black eyes were placed on little prominences 

 at the bases of the tentacles. The upper part of the hinder end of the 

 foot supported a horny, ovate operculum, which closed the aperture when 

 the animal withdrew into the shell. 



Professor Parker explained that in the water-breathers, including the 

 fresh-water and marine mollusks, the proboscis is of two kinds : in one, 

 it is simply contractile that is, it can be contracted as when one 

 presses a cushion spring together while in the second class, it 

 is retractile, and can be retracted like the eye-peduncle of a land snail. 

 The genus Pleurocera is a good example of the first class, and the Dolmm, 

 or tun-shell, of the second class. 



This small snail differed from the ones which had been previously 

 collected not only in breathing by gills instead of by lungs, but also in 

 having an operculum, and in having the 

 mouth placed at the end of a snout. " These 

 differences," Professor Parker remarked, ''are 

 characteristic of most fresh-water snails." 



On one side of the miniature peninsula 

 were a number of rounded objects half buried 

 in sand, and of a rich green color. Upon 

 investigation they proved to be a species of 

 the apple snail, Campeloma decisum. The 

 shell of this snail was of a beautiful apple- Shell and operculum of ap- 



i ,, ,, pie snail, Campeloma decisum. 



green, the whorls were gracefully rounded, (Binney.) 



15 



