200 Darwin, and after Darwin. 



Near the village of Steinheim, in Wiirtemberff, 

 there is an ancient lake-basin, dating from Tertiary 



1 



20 





81 



23 28 



^ 



2C 



CS) — c^-c^<^ 



III 



t'lG. 89, — Transmutations of Planorbis. (After Hyatt.) 



times. The lake has long ago dried up ; but its 

 aqueous deposits are extraordinarily rich in fossil 

 shells, especially of different species of the genus 



