88 LIMNiEIDiE. 



Swansea, the last whorl only is separated from the rest 

 and curled upwards. In the last-mentioned locality 

 there was a great deal of mud which had been brought 

 down by a stream and deposited in the grassy pool where 

 I found the shells. This mud must have inconvenienced 

 the mollusk and prevented its completing the spire of 

 its shell on the usual plane ; so that it gave the last whorl 

 an outward twist, apparently in order to get clear of the 

 incumbrance. When the drains and splashy pools in 

 which this kind of Planorbis lives are dried up by the 

 heat of summer, it retires far within its shell and closes 

 the mouth or opening with a yellowish- white and rather 

 solid lid, patiently waiting for the next shower of rain 

 and fasting in the mean time. This species inhabits 

 Siberia, and ranges as far south as Algeria and Sicily. 



It differs from P. glaber in the whorls being much 

 narrower and consequently more compact, and in usually 

 having a blunt keel on the periphery. 



The typical or ordinary form is the P. rotundatus of 

 Poiret, P. vortex var. ^. of Draparnaud, and P. leuco- 

 stoma of Michaud, besides having other specific names 

 for several of the varieties. 



7. P. vor'tex"^, Linne. 



Helix vortex, Linn. Sjst. Nat. ed. xii. p. 1243. P. vortex, F. & H. iv. p. 157, 

 pi. cxxvii. f. 6-8. 



Body reddish-brown, with a slight tint of violet, rather 

 distinctly marked with minute black specks : tentacles very 

 long, slender and finely pointed : foot evenly rounded in front 

 and keeled behind. 



Shell much compressed, concave above and flat below, thin, 

 glossy, yellowish or greyish-horncolour, finely and closely 

 striate in the line of growth, and occasionally having a few 

 obscure and extremely minute spiral stria3 : epidermis thin : 



* Whirlpool. 



