24 HiCKLiNG, Variation of Planorbis viultifoiviis, Bronn. 



Plate II. 



Fig. 4. — Series of very young shells showing the variation pro- 

 duced by the development or otherwise of carinse. 

 The upper and lower rows represent the same shells. 

 A is the primitive smooth form. It will be seen that 

 the dorsal carina develops first, the ventral one later. 

 Compare with Text-Jigs. 4-6. x 37 dia. 



Fig. 5. — Three mature shells of height G {Fis^. i), showing 

 variation of apex. Compare with preceding figure. 

 Apex of A = A or B of Fig. 4 ; apex of b = d of Fig. 4 ; 

 apex of c= F or G of Fig. 4. x 37 dia. 



Fig. 6. — Mature shells showing variation in form of apex, in 

 high (a, b) and low (c, d) forms, x 2-3 dia. 



Fig. 7. — Series of mature shells showing variation in form of 

 aperture. x 17 dia. 



Fi<[. 8. — Plajwrbis Stei/iheime?isis (?) associated with the fore- 

 going shells. These forms agree almost completely 

 with Fig. 4 A except in size, but are not linked by 

 any intermediates to the mature discoid forms of 

 P. multiformis. ^37 dia. 



