EXPLANATION OF PLATE IV. 



Abnormal examples of Planorbis spirorbis Mull. 



Collected by A. G. Stubbs at Tenby. 



(See page 106). 



Row i. — Shells irregular ovals with gaps between the whorls. 



,, 2. — Shells normal, except last whorl which is bent away at 

 various angles. 



„ 3. — Shells tangled and irregularly knotted. 



,, 4. — Shells perfectly scalariform and mostly regularly coiled ; the 

 first two specimens in Row 5 belong to this form. 



,, 5. — Last three specimens sinistral as well as scalariform. 



