. Birds and nature . water. They have been found at a heightof over fourteen thousand feet in Thibetand at a depth of eight hundred feet inLake Geneva, Switzerland. Duringtimes of drought when the streams aredried up and the surface of the mud issun-cracked, the species of this familybury themselves deeply in the mud andcover the aperture with an epiphragm, inmuch the same manner as the land fact accounts for the apparent disap-pearance of all life from a pond when itdries up, and its sudden and seeminglyunaccountable reappearance when thepond is again filled with water. A genus of
. Birds and nature . water. They have been found at a heightof over fourteen thousand feet in Thibetand at a depth of eight hundred feet inLake Geneva, Switzerland. Duringtimes of drought when the streams aredried up and the surface of the mud issun-cracked, the species of this familybury themselves deeply in the mud andcover the aperture with an epiphragm, inmuch the same manner as the land fact accounts for the apparent disap-pearance of all life from a pond when itdries up, and its sudden and seeminglyunaccountable reappearance when thepond is again filled with water. A genus of pond snails closely alliedto Limnaea, but having discoidal orspiral shells, is Planorbis, the flat-orbshells. Instead of dragging their shellsafter them, as in the last genus, they carrythem perfectly perpendicular, or perhapstilted a little to one side. The animalsare very rapid in movement, more so thanLimnaea, which are rather delight in gliding rapidly about, 128 . LIBRARYUWIVfck5ll> Of ILLINOIS. Physa pyrina (U. S.) Melania tetrica (Viti Islands.) Angitrema verrucosa (U. S.) Planorbia trivolvia i r. 8.) Pleurocera elevatum fU. s.) Ampullaria depressa (U. 8.) LImnaea BtagnaMa r. 8.) Vivipara coutectoides (U. 8.) Campeloma subaolidum <U. S.) Limnaea mcgasoma (U. S.) their long, filiform tentacles waving aboutlike a whip in the hands of an impatientdriver. The Limnaeas of which we have beenspeaking have mostly dextral or right-handed shells, that is, have the apertureon the right side when you hold the shellin the position pictured on our plate. Inthe family Physidae the shell is left-hand or sinistral. The members of thisfamily have shining, horn-colored shells,more or less fusiform. The tentacles arelong and filiform and are constantly mov-ing about as in the allied genus Planorbis,The animal is very active and movesabout with a steady, gliding motion. Itis very interesting to watch a number ofPhysae in an aquarium; as they arecrawling along the bottom,
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