their long, filiform tentacles waving about a long rostrum, or proboscis, and not in 



like a whip in the hands of an impatient the lower plane of the head, as in the first 



driver. class. Among the most common of this 



The Limnaeas of which we have been class are the river snails, known as Stre- 

 speaking have mostly dextral or right- pomatids. There are about three hun- 

 handed shells, that is, have the aperture dred species in this family, and with two 

 on the right side when you hold the shell or three exceptions they are confined en- 

 in the position pictured on our plate. In tirely to the United States in geograph- 

 the family Physidae the shell is left- ical distribution. The shells are more or 

 hand or sinistral. The members of this less graceful, having long, turreted spires / 

 family have shining, horn-colored shells, and small apertures. The color of the 

 more or less fusiform. The tentacles are shells is generally a uniform greenish or 

 long and filiform and are constantly mov- yellowish, although some species have 

 ing about as in the allied genus Planorbis. color bands, and the aperture is frequent- 

 The animal is very active and moves ly tinged with purple; or reddish, 

 about with a steady, gliding motion. It The animal is ver^ interesting in cap- 

 is very interesting to watch a number of tivity. It is not very bold and will lie on 

 Physae in an aquarium ; as they are the bottom of an aquarium with its head 

 crawling along the bottom, one will be and foot half protruding from its shell, and 

 seen to rise suddenly to the top of the its rostrum and tentacles slowly moving 

 water and move along with the foot ap- about. Frequently it may be seen mov- 

 plied to the surface, the shell hanging ing along with its head and rostrum bent 

 down. Again, they may be seen descend- down and moving about like a hound on 

 ing, suspended by a thin thread of mucus, the scent, 



When the animal rises suddenly, the A family closely allied to the last is the 



branchial cavity which contains the lung Melaniidae, the animals of which inhabit 



is heard to open with a faint, clicking the entire world, except North America, 



sound, which is probably due to the pres- They may be distinguished from the last 



sure of air in the lung being suddenly lib- family by the presence of little finger-like 



erated. Several of the species of Physa digitations on the edge of the mantle, 



inhabit water as cold as the freezing point The shells are generally larger and more 



and they may be frequently seen in win- highly colored than those of the last fam- 



ter gliding over the bottom of a stream ily, many of them being of a dark choco- 



or pond when the surface is frozen. The late color and some are of a beautiful 



little glairy, transparent masses of jelly- glossy black ; some shells are smooth, 



like matter which are seen attached to while others are ornamented by knobs 



stones and the under side of sticks, are and spines. The genus Melania, a 



.he eggs of Physa or Limnaea. species of which is illustrated on the plate 



Not all of the fresh-water pulmonates accompanying this article, is the most 



have spiral shells. A whole family, the characteristic form. 



Ancylidae, have a conical shell formed The largest and handsomest of the 



like a rounded shield, and resembling the fresh-water snails belong to the two fam- 



limpets, hence called the river limpets, ilies Viviparidae and Ampullariidae, the 



They are generally quite small and live shells of the latter family frequently at- 



attached to the interior of dead river taining a length of three inches. The ani- 



shells and to submerged plants and to mals of the first family prefer a sandy 



rocks. They are very interesting, but beach in a large lake or river, while those 



hard to find on account of their small of the second generally live in more or 



size and inconspicuous habitat. less muddy rivers, ponds and creeks. A 



The second class of mollusks or those single genus of Viviparidae (Campelona) 

 that breathe air through the water, have is confined solely to the United States, 

 a respiratory cavity instead of a lung, east of the Rocky Mountains. Their 

 in which is placed a series of leaflets, ar- shells are generally of a rich grass green 

 ranged like the teeth of a comb in two and in certain localities they may be col- 

 series of lines, forming the so-called gills, lected by the thousands. Unlike many of 

 The mouth, also, is placed at the end of the snails of which we have been writing, 



131 



