MARIS A. 347 



operculum, which latter, moreover, is entirely horny. 

 The species inhabit the lakes and rivers of warm coun- 

 tries, more especially those of South America and the 

 West Indies. In the drj' season, they bury themselves 

 deeply in the mud, where they remain in a state of tor- 

 pidity, and on account of their possessing a pulmonary 

 cavity in addition to the gills, they are enabled some- 

 times to survive a considerable period after having been 

 removed from the water. The South American Indians 

 term them " Idol shells," and are said to hold them in 

 great veneration. 



Species of Pomus. 



angulata, Jonas. Largillierti, Phil. 



balauoidea, Gould. malleata, Jonas. 



canaliculata, Lam. margiuata, Jonas. 



Cecillii, Phil. papjracea, Sjjix. 



conica, Wood. Rossii, D'Orb. 



c^'clostoma, Spix. scalaris, D'Orb. 



decussata, Moric. teres, Phil. 



insularura, D'Orb. urceus, Midi. 



intermedia, Feruss. zonata, Wagn. 



Genus MARISA, Gray. 



Siphon elongate. 



Operculum horny, dextral. 



Shell dextral, depressed, discoidal, deeply and widely 

 umbilicated ; spire very short, whorls rounded ; aperture 

 suborbicular, entire, peristome thin, simple. 



Syn. Ceratodes, Guild. Marissa, Menke. 



Ex. M. cornu-arietis, Linncsus, pi. 37, fig. 3. Oper- 



