186 TKESH-WATEE AQUAEIA. 



Mr. Darwin, in his " Origin of Species," speaks of an Ancylus 

 as taring been taken adhering to a water-beetle — a Dytiscus. 

 A good way to obtain these interesting little molluscs is to 

 take up and examine the flat stones at the bottom of clear and 

 shallow streams, to which they will be found adhering. It is 

 necessary to exercise a little care in removing Ancyli, or they 



may be hurt. They give no 

 trouble in the aquarium, where 

 they spend nearly all their time 

 upon the sides, feeding upon 

 confervas. The body of the 

 animal is greyish, and the ten- 

 FiG. 123. Ancylus fluviatilis. tacles are greyish-white and 



broad at their base. The shell, 

 which is described as cowl-shaped, covers all the animal when 

 it is moving, except the tips of the tentacles, and sometimes 

 perhaps a portion of the muzzle. It is a dark horn-colour, 

 and about Jin. in diameter. The spire is curved towards the 

 right. The apex is rather blunt, and the aperture is oval. 

 This moUusc lays about eight eggs, and incloses them in a 

 roundish capsule. The eggs are hatched in about twenty-six 

 days. 



Ancylus ohlongus lives in slow-running or stagnant clear 

 water throughout Britain, but it is rather local. It is found 

 adhering to the under-side of aquatic plants, and not, like A. 

 fluviatilis, to stones and wood. When it moves, which is seldom, 

 it travels more quickly than the last species. It has a yellowish- 

 grey body, with a greenish tinge. The tentacles are light grey, 

 and widely separate from each other. The shell is more oblong 

 than the last species ; hence the specific name. It is about Jin. 

 in diameter, and of a glossy yellowish-green horn-colour. The 

 spire is bent towards the left, and not, as in the A. fluviatilis, 

 towards the right. The apex is rather sharp, and the aperture is 

 oval. The eggs are from four to twelve, and are inclosed in an 

 orbicular capsule. They are hatched in about twenty-six days. 



