PLANORBIS. 87 



C. Whorls many, keeled. 

 6. P. SPIROR'BIS*, Miiller. 



P. spir&rbis, Mull. Verm. Hist. pt. ii. p. 161 ; F. & H. iv. p. 159, 

 pi. cxxvii. f. 9, 10. 



BODY purplish-grey or reddish-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 

 horncoJbur, closely striate in the line of growth, and marked 

 spirally with very faint and minute striae : epidermis thin : 

 periphery angular, and sometimes bluntly keeled on the 

 lower side : whorls 5-6, 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 cir- 

 cular, often thickened 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. 



Var. ecarinata. Shell smaller, light grey, having one 

 whorl less than usual and no trace of a keel. P. spirorbis, 

 Moq.-Tand. Hist. Moll. 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 

 istortion which I found in Bishopston Valley, near 



* Round-spired. 

 O 



