2 LAND AND FRESH-WATER SHELLS OF N. A. [PART III. 



truly ampliibious, and to be enabled to survive a long drought, 

 and have been known to revive after having been kept seve- 

 ral years out of water. The long siphonal tube appears to 

 be formed by the left neck-lappet, which is seen in the Vivi- 

 paridee in a rudimentary state. 



But one genus of this family is represented in North America. 

 lu order, however, that the others may be understood by those 

 not liaving access to the more recent works on general Conchology, 

 I have added below the descriptions of 11. & A. Adams. 



Genus Ampullaria. — Respiratory siphon elongate. Oper- 

 culum horny, with an external shelly coat. Shell globose, 

 umbilicated ; spire small, last whirl ventricose ; aperture 

 oblong, entire, peristome continuous, slightly reflexed, with 

 an internal thickened rim or ledge. 



Genus Pomus, Humphrey, characterized as below. 



Genus Marisa, Gray. — Siphon elongate. Operculum horny, 

 dextral. Shell dextral, depressed, di,-coidal, deeply and 

 widely umbilicated ; spire very short, whirls rounded ; 

 apertifre suborbicular, entire, peristome thin, simple. 



Genus Pomella, Gray. — Operculum horny, dextral. Shell 

 solid, si)ire short, whirls transversely striated, the last very 

 large ; aperture semi-ovate, inner lip concave, broad, flat- 

 tened, peritreme simple, acute. 



Genus Lanistes, Montfort. — Operculnm horny, sinistral, 

 or with the nucleus on the left margin. Shell depressed, 

 thin, sinistral, deeply and widely umbilicated ; spire short; 

 aperture oblong, entire ; inner lip expanded over the last 

 whirl, peristome simple, acute. 



Genus Meladomus, Swainson. — Operculum horny, sinis- 

 tral. Shell sinistral, thin, imperforate, covered with a 

 dark olivaceous epidermis ; spire produced, acuminated ; 

 aperture oval, reversed, contracted and acute posteriorly, 

 entire in front, peristome thin, simple. 



Genus Asolene, D'Orbigny. — Siphon not exposed. Oper- 

 culum horny, with an internal shelly coat. Shell globose, 

 solid; spire small, whirls rounded ; aperture oval, entire ; 

 inner lip slightly thickened, peritreme simple, acute. 



