their long, filiform tentacles waving about 

 like a whip in the hands of an impatient 

 driver. 



The Limnaeas of which we have been 

 speaking have mostly dextral or right- 

 handed shells, that is, have the aperture 

 on the right side when you hold the shell 

 in the position pictured on our plate. In 

 the family Physidae the shell is left- 

 hand or sinistral. The members of this 

 family have shining, horn-colored shells, 

 more or less fusiform. The tentacles are 

 long and filiform and are constantly mov- 

 ing about as in the allied genus Planorbis, 

 The animal is very active and moves 

 about with a steady, gliding motion. It 

 is very interesting to watch a number of 

 Physae in an aquarium ; as they are 

 crawling along the bottom, one will be 

 seen to rise suddenly to the top of the 

 water and move along with the foot ap- 

 plied to the surface, the shell hanging 

 down. Again, they may be seen descend- 

 ing, suspended by a thin thread of mucus. 

 When the animal rises suddenly, the 

 branchial cavity which contains the lung 

 is heard to open with a faint, clicking 

 sound, which is probably due to the pres- 

 sure of air in the lung being suddenly lib- 

 erated. Several of the species of Physa 

 inhabit water as cold as the freezing point 

 and they may be frequently seen in win- 

 ter gliding over the bottom of a stream 

 or pond when the surface is frozen. The 

 little glairy, transparent masses of jelly- 

 like matter which are seen attached to 

 stones and the under side of sticks, are 

 the eggs of Physa or Limnaea. 



Not all of the fresh-water pulmonates 

 have spiral shells. A whole family, the 

 Ancylidae, have a conical shell formed 

 like a rounded shield, and resembling the 

 limpets, hence called the river limpets. 

 They are generally quite small and live 

 attached to the interior of dead river 

 shells and to submerged plants and to 

 rocks. They are very interesting, but 

 hard to find on account of their small 

 size and inconspicuous habitat. 



The second class of mollusks or those 

 that breathe air through the water, have 

 a respiratory cavity instead of a lung, 

 in which is placed a series of leaflets, ar- 

 ranged like the teeth of a comb in two 

 series of lines, forming the so-called gills. 

 The mouth, also, is placed at the end of 



a long rostrum, or proboscis, and not in 

 the lower plane of the head, as in the first 

 class. Among the most common of this 

 class are the river snails, known as Stre- 

 pomatids. There are about three hun- 

 dred species in this family, and with two 

 or three exceptions they are confined en- 

 tirely to the United States in geograph- 

 ical distribution. The shells are more or 

 less graceful, having long, turreted spires 

 and small apertures. The color of the 

 shells is generally a uniform greenish or 

 yellowish, although some species have 

 color bands, and the aperture is frequent- 

 ly tinged with purple or reddish. 



The animal is very interesting in cap- 

 tivity. It is not very bold and will lie on 

 the bottom of an aquarium with its head 

 and foot half protruding from its shell, and 

 its rostrum and tentacles slowly moving 

 about. Frequently it may be seen mov- 

 ing along with its head and rostrum bent 

 down and moving about like a hound on 

 the scent. 



A family closely allied to the last is the 

 Melaniidae, the animals of which inhabit 

 the entire world, except North America. 

 They may be distinguished from the last 

 family by the presence of little finger-like 

 digitations on the edge of the mantle. 

 The shells are generally larger and more 

 highly colored than those of the last fam- 

 ily, many of them being of a dark choco- 

 late color and some are of a beautiful 

 glossy black ; some shells are smooth, 

 while others are ornamented by knobs 

 and spines. The genus Melania, a 

 species of which is illustrated on the plate 

 accompanying this article, is the most 

 characteristic form. 



The largest and handsomest of the 

 fresh-water snails belong to the two fam- 

 ilies Viviparidae and Ampullariidae, the 

 shells of the latter family frequently at- 

 taining a length of three inches. The ani- 

 mals of the first family prefer a sandy 

 beach in a large lake or river, while those 

 of the second generally live in more or 

 less muddy rivers, ponds and creeks. A 

 single genus of Viviparidae (Campelona) 

 is confined solely to the United States, 

 east of the Rocky Mountains. Their 

 shells are generally of a rich grass green 

 and in certain localities they may be col- 

 lected by the thousands. Unlike many of 

 the snails of which we have been writing, 



131 



