1918.] N. Annandale : Molluscs of the Inle Lake. 



177 



The knobs, ridges and spines on the shell of Taia intha, the cul- 

 minating species of the genus, seem to be of no use to the animal, which 

 is a sluggish creature, quite incapable, so far as it is possible to judge, 

 of aesthetic perception of its own beauty. Its shell has reached perfec- 

 tion in calm and undisturbed surrovmdings, which place no bar in the 

 path of eccentricity. The sculpture seems to have made its appearance 

 in a primitive form in T. fheohaldi in circumstances that forbade its full 

 development, and to have had a cumulative development in proportion 

 as the surroundings became more and more peaceful and settled. 

 Lack of enemies, abundance of food, absence of aquatic currents, abund- 

 ance of free oxygen, an equable temperature without frost, absence of 

 free acid and erosive algae have all combined to give an inherent 

 tendency full play, probably not through the elimination of individuals 

 in which this tendency was feeble so much as through its streno-then- 

 ing in all individuals. 



The Inle Lake, or rather the system as a shrunken relic of which it 

 persists, was, on a comparatively small scale, one of those districts, 

 such as Lake Tanganyika or the lake country of Celebes, in which phe- 

 nomena of the kind have been manifested to an exceptional deoree. 



List €J species giving approximate 



Fossil. 



age, etc. 



Succinea indlca, Pfeiffer 



Limnaea andersoniana, NevilJ 

 „ shaiiensis, Annandaie, A 

 „ „ , B 



, C 

 „ „ , D 



,, mimetica, Annandaie 

 „ ? prox. ovalis Gray 



Planorbis exustus, Deshayes 



„ saitjoaensis, Crosse and 



„ veiifer, Annandaie 



„ ,, var. ciliata 



„ trochoideus, Benson 

 „ calathus, Benson . 

 ,, caenosus, Benson . 



Mdania tuberculata (Miiller) 



Fischer 



in streams and pen Is. 



