

PLANORBIS. 87 



C. Whorls many, keeled. 

 6. P. spiror'bis^_, Miiller. 



P. spirorhis, Miill. Verm. Hist, pt.ii. p. 161 ; F. & H. iv. p. 159, pi. crxvii. 

 f.9, 10. 



Body purplish-grey or redclish-brown, with minute black 

 specks on the foot : tentacles rather long, slender and pointed : 

 foot short and narrow, obtusely rounded in front and angular 

 behind. 



Shell slightly concave above and flat below, or vice versa, 

 slightly wider at the base, rather solid, glossy, brownish horn- 

 colour, closely striate in the line of growth, and marked spirally 

 with very faint and minute striog : epidermis thin : periphery 

 angular, and sometimes bluntly keeled on the lower side : 

 whorls b~Q, gradually increasing in size, the last not exceeding 

 in diameter one-sixth of the whole spire ; they are rounded, 

 but angular : suture deep : mouth nearly circular, often thick- 

 ened or strengthened inside by a rib : outer lip very slightly 

 reflected : inner lip continuous with the other lip, but spread 

 over the columella : umbilicus very large and shallow. L. 0*04. 

 B. 0-25. 



Yar. ecarinata. Shell smaller, light grey, having one whorl 

 less than usual and no trace of a keel. P. spirorhis, Moq.- 

 Tand. Hist. MoU. Fr. p. 437, pi. xxxi. f. 1-5. 



Habitat : On plants and grass in shallow and stag- 

 nant water everywhere from the Moray Firth district to 

 the Channel Isles. It is also a fossil of our upper ter- 

 tiary beds. The variety appears to be very rare in this 

 country. I have only found it once ; and that was in 

 Oxwich marsh, near Swansea. A monstrosity not un- 

 frequently occurs, in which the whorls are more or less 

 twisted and separated. Some specimens which my late 

 friend Mr. Barlee found at Penzance resemble a minute 

 corkscrew; and in another form of the same kind of 

 distortion which I found in Bishopston Valley, near 



* Round-spired. 



