GASTEROPODA ! LIMNEID^E. 487 



world-wide, and of which there are four thousand living 

 species, and three hundred fossil. * 



LIMACID.E, OR SLUG FAMILY. Fi s 432. 



This Family comprises terrestrial 



Which have the Shell Lima* campestru, Binney. 



small or rudimentary, and usually 



internal. Seventy living and a few fossil species. 



LIMNEID^:, OR POND-SNAIL FAMILY. This Family 

 contains gasteropods which have the shell thin and horn- 



Fig. 433- 



Fig. 435- 

 Fig- 434- 



Planorbis lentus, Say. 



United States. L ^^ desidiosat 



Physa heterostropha, Say. United States. 



United States. 



colored, and capable of containing the whole animal when 

 retracted. Limnaeids inhabit fresh water, and deposit 

 their spawn in oblong transparent masses on aquatic 

 plants and stones. There are one hundred and sixty liv- 

 ing and about as many fossil species. 



AURICULID,E. This Family comprises gasteropods 

 which have the shell spiral, with a horny epidermis, and 

 the body whorl large. Fifty or sixty species are known. 



CYCLOSTOMID.E. This Family embraces seven hun- 

 dred species of gasteropods, whose general form is shown 

 by Figs. 436, 437. Twenty fossil species. Terrestrial. 



Fig- 437- 

 Fig. 436. 



Helicina orbiculata, Say. ^rr ' Aciculofuua, 



United States. Walker. Britain. 



Cydostoma dentatum. 

 United States. 



ACICULID^. This Family contains gasteropods which 

 have the shell long and cylindrical. Twenty-five species. 



