i6i 



THE 



JOURNAL OF CONCHOLOGY. 



Vol. 13. APRIL, 1911. No. 6. 



A DOUBLE-MOUTHED CLAUSILIA BIDENTATA NEAR 

 WARTON, WEST LANCASHIRE. 



I!y J. WILFRID JACKSON, F.G.S. 



(Read before the Society, September 14th, 19T0). 



Whilst examining a mossy wall at Yealand Conyers, near Warton, 

 one wet day a few weeks ago, I had the good fortune to discover a 

 rather fine example of Clausi/ia bidentata which possesses an ad- 

 ditional or second aperture. 



The animal was busy climbing the wall in search of food at the time 

 of its capture, and I noticed that its body protruded from the 

 secondary mouth, which is situated about half-a-whorl distant from 

 the ori2;inal one, and faces to one side. 



Whether the formation of this second aperture is due to some de- 

 rangement or obstruction of the clausium or not, is very difficult to 

 decide. The new mouth is quite perfect and well formed, but only 

 partially covers the hole pierced in the shell-wall, the jagged edge of 

 which shows at one side (see figure). 



Dual-mouthed examples of this species are not uncommon ; one 

 from Luton, Bedfordshire is figured by Mr. J. W\ Taylor in his 

 " Monograph of the Land and Freshwater MoUusca of the British 

 Isles," vol. i. (1900), p. 119. Some further remarks on this pheno- 

 menon will also be found in the " Lancashire Naturalist," Nov., 1910, 

 pp 275-276, and Dec, 1910, p. 307. 



