LIMN^ID^. 101 



individaal is able, at the same time, to perform the function of 

 each sex with two others. 



Bulimnsea megasoma, Say (ciii, 5), is partially carnivorous 

 ( Wetherby . Mr. Whitfield has recorded some singular changes 

 produced in successive generations, the progeny of a single indi- 

 vidual, confined in an aquarinm. They graduall}^ diminished in 

 size and the male organs disappeared. Prof. Hyatt has ascribed 

 these changes to different conditions of temperature, but it was 

 probably due also to deficient food-supply, and an effect of the 

 phj^siological law to which Mr. Meehan has so frequently called 

 attention in plants, namely, of the greater persistence, in cases 

 of depauperization, of female functions and members. 



LYMNUS,Montf. Typical. (Auricula, Klein.) L. stagnalis^ljmii. 

 (ciii, 9). 



RADIX, Montf., 1810. (Neristoma, Klein [teste Adams]. 

 Gulnaria, Leach [teste Turton].) Shell suboval-globular ; last 

 whorl ventricose ; aperture very large ; columella plaited. L. 

 am'icularia, Linn, (ciii, 6). 



POLYRHYTis, Meek. Much like the last in form, but bearing 

 distinct, regular, vertical costse. L. Kingi, Meek. Tertiary ; 

 Utah. 



BULiMNiEA, Haldeman, 1841. Shell oval, subgiobular, large, 

 the spire short, apex sharp ; aperture moderate. L. miegasoma^ 

 Say (ciii, 5). 



LiMNOPHYSA, Fitzingcr, 1833. Shell oval-oblong, spire elevated ; 

 aperture narrowly' ovate, abont half the length of the shell. L. 

 rejlexa^ Say (ciii, T). 



LEPTOLIMN^A, Swainson, (Omphiscola, Eaf. ) Shell nearly 

 cj'lindrical ; spire thick, lengthened ; aperture small. L. glabra^ 

 Miill. 



ACELLA Hald., 1841. Shell elongated, very slender; whorls 

 4-6, very oblique, but slightly convex; aperture small, ovate, 

 expanded below. L. gracilis^ Jay (ciii, 8). 



PLEUROLiMN^A, Meek. Shell differing from the last in having 

 small, regular surface-costse parallel to the lines of growth, 

 and aperture narrowed or subangular, instead of rounded ante- 

 riorly. L. tenuicostata, Meek and Hayden. Fossil. Eocene; 

 Dakotah. ? = Acella. 



VELUTiNOPSis, Sandberger. Oval, neritiform, spire excavated, 

 last whorl ver^^ large, columellar lip depressed. L. velutina. 

 Desh. Tertiary ; Crimea. 



Some of the species of Limnaea inhabiting the Sandwich 

 Islands and New Zealand are sinistral, Limnrea adapts itself to 

 very diverse conditions; it is found in Greenland and Iceland, 

 in hot and sulphurous springs, in fresh or brackish water. L. 

 Hookeri occurs in Thibet, at an elevation of nearly 14,000 feet ; 

 L. abyssicola in the Lake of Geneva, at a depth of 800 feet. 



