FRESH-WATER LIMPETS. 115 



The interior muscle scar is divided on one side by a 

 siphonal groove, but this mark is not always very 

 distinct. This little mollusk lives upon rocks, between 

 tides, and is quite rarely found. When disturbed, it 

 gives out a milky fluid. 



Now we will turn from the saltwater for a little 

 while and study the similar mollusks which live in 

 the lakes and rivers. 



The first one we meet is very small, only one-eighth 

 of an inch across and one-fourth of an inch long. It 

 is the fresh-water Limpet, Ancylus fragilis, Tryon, 

 An-sy'-lus frag'-il-is. The shell is Limpet-shaped, 

 narrow, thin, and of a light brown color. From 

 Portland, Oregon. 



Ancylus subrotundus, Tryon, sub-ro-tun'-dus. Sim- 

 ilar to the last, but more oval in outline. From The 

 Dalles. 



Acroluxus Nuttalli, Hald^Ac-ro-lux'-us Nutt-all'-i, 



^~m Fig. 102. The shell is Limpet- shaped, 

 ^^ nearly circular in outline. Brown, thin 



Fig. 102. an( j translucent, one-fourth of an inch or 

 more in diameter; associated with the last species. 



Gund lachia Californica, Rowell, Gund-lak'-i-a Cal- 

 i-for'-ni-ca. Very minute, limpet-shaped, with a 

 small shelf across part of the aperture. It is found 

 on the stems of plants growing in stagnant ponds. 



There are mollusks in almost every brook and 

 pond in the country. Every boy will be sure to find 

 them if he carefully turns over the stones and 

 examines the old sticks and leaves which have fallen 

 into the water. 



They feed almost wholly upon vegetable matter ; 

 some of them eat the green confervce, that is, the 

 slimy vegetation which abounds in stagnant water. 



