VALVATA. 



TESTA univalvis, spiralis, spira discoidea vel 

 elevatiosciila, anfraetibus rotundatis; apertura 

 circular!, peiitremate continuo acuto; operculo 

 corneo spirali, anfraetibus numerosis, confertis. 



Found only, as far as hitherto we have been able to learn, 

 in ditches, lakes and other freshvvaters in the northern 

 hemisphere; Britain and other countries in Europe possess 

 several species, and in North America some abound both 

 in a recent and fossil state. Few species are known, all 

 of which are small shells; they generally have much the 

 appearance of Planorbes or Cj/clostomata, from the former 

 they may, however, easily be distinguished by their hav- 

 ing a circular aperture; and from the latter, by their 

 being freshwater, and not land shells. We have never 

 met with any other fossil species than those of a very 

 recent lacustrine formation in Canada, and another in a 

 volcanic stone from Auvergne, which we have represented. 



Shell univalve, spiral, spire discoidal or only slightly 

 elevated, v/ith rounded volutions; aperture circular, not 

 modified by the last volution, peritreme acute, sharp 

 edged, continuous; operculum horny, spiral, its volutions 

 numerous and close-set. 



