New or Little Known North American Limnceidoe. 



99 



glahratus. Not being uncertain, at that time, as to the identity of the 

 shells in 1113' cabinet under the name of P. gfabratus, I supposed the 

 shells now referred to that species to be new; they have been so called 

 by others, but I am now satisfied that they are the true P. glabra tus of 

 Say, and that they will assist in removing any of the uncertainties cling- 

 ing about that species. As will be seen by the specimens exhibited, 

 they have five whorls, they are not carinate, the whorls Increase in size 

 very graduall}^ the umbilicus exhibits all the volutions, the shells are 

 polished, and they meet, in every way, the requirements of Mr. Say's 

 description. It is highly probable, therefore, that the species has not, 

 hitherto, been correctly identified. The species has the southern dis- 

 tribution of many of Mr. Say's shells, and together with the P. lentus 

 has probably not been found in northern waters. 



Planorbis (Helisoma) durti, nov. sp. (fig. 4). 



Shell thick, shining, straw color, of medium size, slightly waved by 

 indistinct transverse ridges, which upon close examination are seen to 



Fig. 4. 



be made up of from five to seven lines of Increment. Whorls about 

 four, rapidly enlarging, the last carinate above to the labrum, sub- 

 carinate or obtusely rounded below. Spire very regular, flat or very 

 slightl}^ concave. Its outer whorl is sometimes slightly raised on the 

 side before the aperture. Umbilicus deep and narrow, not exhibiting 

 all the volutions. Peristome acute, sharply angular above, forming the 

 upper carina of the body whorl, less acutely angular below, and de- 

 flected upward so as to meet the body whorl at one-third the distance 

 from its base, thus approximating its upper extremity. The lower 

 margin of the aperture is pi'oduced beyond the upper, thus rendering 

 the aperture very oblique in profile. 



Remarks. 



This shell was given me several years ago, by Mr. Charles 

 Dury, who brought it from the Everglades of Florida. It was 

 also among the shells received from the Miami country. It is 



