336 



RISSOID.E. 



with the eyes at their outer bases; the opereuligerous 

 lobe is simple, and the shells are thin and covered with an 

 epidermis. 



Species of Hydrobia. 



aculeus, Gould. 

 acuta, Drap. 

 anatina, Jeffr. 

 antbracina, Mir/h. 

 antipodarum, Gray. 

 badia, Gould. 

 castanea, Moll. 

 ciliata, Gould. 

 cincta, Gotdd. 

 cingulata, Midd. 

 corolla, Gould. 

 coronata, Pfeiff. 

 crystallina, Pfeiff. 

 Egena, Gould. 

 Ferussiua, Besm. 



gracilis, Gould. 

 Jamaicensis, C. B. Adams. 

 nigra, Quoy and Gaim. 

 parvula, Goidd. 

 pornicta, Migh. 

 Preissii, Phil. 

 saxatilis, Moll. 

 scrobiculata, Moll. 

 spinifera, C. B. Adams. 

 spinulosa, Goidd. 

 subumbilicata, Mont. 

 ulvse, Penn. 

 unicolor, Oliv. 

 ventricosa, Mont. 

 Zealandiae, Gray. 



Genus AMNICOLA, Gould and Haldeman. 



Shell thin, turbinate, covered with an epidermis, axis 

 perforated, whorls rounded ; aperture circular, peritreme 

 continuous ; outer lip simple, acute. 



Ex. A. porata, Say, pi. 35, fig. 11. Operculum, A. 

 porata, fig. 11, a. 



This genus comprises a suite of small fresh-water 

 Mollusks with thin, umbilicated shells having rounded 

 whorls ; the species appear to be most numerous in North 

 America ; the position of the eyes, which are stated to be 

 sessile at the outer bases of the tentacles, will distinguish 

 them from Paludinella, which they very much resemble 

 as regards the shell. 



