102 LAND AND FRESII-AVATER SHELLS OF N. A. [PART III. 



lip straight, flattened, tLe margin smoutb or denticulated ; outer 

 lip simple internally. 



The Neritellse are tolerably numerous in species ; they are 

 inhabitants of fresh water, and are usually covered with an 

 epidermis ; some among them are found crawling on the stones 

 in shallow water ; others live in deeper water, half buried in the 

 mud, some in brackish and others even in salt water ; some are 

 amphibious, clinging to the roots of Nipah palms and other trees 

 on the margins of rivers, while a few inhabit the foliage of tall 

 trees that overhang ponds and rivulets. The genus Neritella, 

 as restricted, is characterized by the shell being transverse, 

 elliptical or hemispherical ; the spire lateral or none ; the inner 

 lip septiform, flattened and striolate, with the margin finely den- 

 ticulate ; with one or two exceptions they are not found in the 

 frigid or temperate zones, but are extensively distributed in 

 every other part of the world. 



I adopt the name Neritella, instead of Neritina, on acco;int 

 of its having precedence. I presume a description was published 

 by Humphreys, but do not have access to a copy of the Museum 

 Colonnianum. Neritella is generally preferred in the more recent 

 works on Conchology. 



The genus Neritella, as restricted by Messrs. Adams, contains 

 no North American species. The following are the subgenera 

 proposed by them, with the American species quoted in each : — 



Subgenus Neritina, Sw. {Clitlion, Recluz). — Shell globular, oval or 

 turriculated, smooth or spirally striated, often adorned with vivid 

 and varied colors ; inner lip septiform, crenulated, rarely simple. 



iV, casxicnhnn. 1 N. suyana. 



N. reclivata. 1 



Subgenus Vitta, Klein (Thcodoxits,UoyTF. ; Elea, Ziegl.).— Shell trans- 

 verse, smooth or nearly smooth ; spire lateral, inclined over the 

 aperture, more or less prominent ; inner lip usually flat, with the 

 margin simple or denticulated ; operculum uniform, without colored 

 zones. 



^V. jnyana. | N. pir.ta. 



Subgenus Dostia, Gray (Sandaliformes, Mitrula, Mke.).— Shell slipper- 

 shaped, solid ; apex entirely posterior, rolled in a half turn on the 



