22 HiCKLING, Variation of Planorbis multiformis^ Bronn. 



DESCRIPTION OF PLATES. 



All the photographs represent varieties of Pla^wrbis multiformis, 

 except photo 8. 



Plate I. 



Fig. I. — Complete set of forms showing variation in height. 

 This is one of the type-sets used as a standard of 

 comparison in sorting, as explained in the text. The 

 shells are full grown. x 1-4 dia. 



Fig. 2. — Three sets of mature shells showing variation in cari- 

 nation. Sets a-d and eh are of height B {Fig. i) 

 and show the ventral and dorsal carinse respectively. 

 The shells i-l are of height G {Fig. i) and show the 

 dorsal carina. The ventral carina is faintly seen in 

 J, but is never strongly developed in " high " shells. 



X 2"3 dia. 



Fig. 3. — Series of inature shells showing variation in degree of 

 overlap (involution) of the whorls. In a and b, note 

 the "shoulder'" and "channelled suture" which arise 

 when the overlap involves the dorsal carina. 



X 2-3 dia. 



