this family is viviparous, that is, brings is thought that at some remote period in 



forth its young alive, instead of laying geological history this lake formed a part 



eggs, as in the family Limnaeidae. This of the ocean and that in the course of 



character has given the family its name, time it was cut off from the sea, grad- 



which is certainly well chosen. When ually became fresh and was finally raised 



born the shell is about one-sixteenth of to its present elevation. The reason for 



an inch in length and is perfectly trans- such a theory is the presence in the lake 



parent. The animal is very active and of certain molluscan organisms whose 



eats voraciously of any vegetation within shells closely resemble those of the salt 



reach. Another handsome shell belong- water family, Littorinidae (Periwinkles), 



ing to this group is the Vivipara contec- The fact that certain species of the family 



toides, which is about an inch in length inhabit brackish water and are even sub- 



and is encircled by several color bands, ject to the influence of fresh water, adds 



It is a common shell in many of our additional weight to this theory. The 



ponds. shell of this species (Limnotrochus 



Somewhat larger and handsomer than thomasi) also resembles certain of the 



the Viviparas are the Ampullarias, or ap- top-shells (Trochus), which are marine in 



pie-shells (also called idol-shells' and habitat. Most of the other species in- 



pond snails). These animals live mostly habiting this lake are like the fresh water 



in tropical and subtropical regions and Viviparas in form. 



are noted for the tenacity with which they The animal of Ampullaria depressa is 

 retain their hold on life. So tenacious of very curious and interesting when studied 

 life are they that instances are known of alive. The foot is very wide, almost 

 their living for several years away from square in some positions ; the head is 

 the water, in this respect resembling some narrow, separated from the body by a 

 of the land snails. It is also recorded that neck and the region of the mouth is pro- 

 hollow pieces of logwood from Honduras duced into two long, cylindrical, tapering, 

 have frequently contained specimens of tentacular processes, which are probably 

 this family alive after a journey of thou- tactile organs like the elongated lips of 

 sands of miles. They may be said to be Glandina, described in the last article. On 

 truly amphibious. the top of the head are placed the two 



The writer has collected in Florida the whip-like tentacles, which are longer than 



large Ampullaria depressa in considerable the length of the whole animal and are 



numbers. It was noted particularly that always waving about when the animal is 



this species furnished the principal food in motion. Just back of the tentacles the 



of the Everglade Kite, a bird inhabiting eyes are placed at the end of two short, 



the southern part of Florida. Large rounded prominences or peduncles, 



quantities of these shells were found From the left edge of the aperture extends 



about the nesting places of these the long, hollow, cylindrical siphon 



birds, from which the animal had been formed by two extensions of the mantle, 



neatly extracted without damaging the On the upper side of the posterior end of 



shell in the least. The bird is, curiously the foot is placed the horny, concentric 



enough, provided with a curved bill which operculum or door. When the animal 



easily fits into the aperture of the mollusk withdraws into its shell the head first dis- 



and extracts the animal with little dif- appears with its appendages and the 



ficulty, and the feet and claws are so con- siphon, and the foot is doubled up in the 



structed that the shell may be firmly held middle, the operculum shutting in last 



during the operation. This shell is fig- and closing the interior against all ene- 



ured on the plate. mies. 



In Central Africa there is a lake, Tan- All of the different groups of the mol- 

 ganyika, having a length of four hundred lusca have their giants and their pigmies 

 miles and a width of from ten to fifty and the fresh-water mollusks are no ex- 

 miles, and at an elevation of twenty-seven ception to the rule. We have thus far 

 hundred feet above sea level, which has studied the animals of normal size and 

 one of the most interesting and peculiar the giants. Let us now turn our attention 

 fresh-water molluscan faunas known. It to some of the pigmies among the fresh- 



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