EXPLANATION OF PLATE XIIL 

 Shells of Hydrobioides nassa (Theobald) and H. physcus, sp. no v. 



Hydrobioides nassa (Theobald). 



Figs. 1, la. — Shells of the subspecies distoma from lake deposit on the 



He-Ho plain, x 4. 

 Fig. 2. — Subfossil shell of the same subspecies from the He-Ho plain, 



X 4. 

 Fig. 3. — Living shell of the forma tyjnca from a pond near Yawnghwe, 



X 4. 

 Figs. 4, ia, 5, 5a. — Shells of the subspecies lacustris from the Inle 



Lake, x 4. 

 Figs. 6, 6a. — Shells of the subspecies rivulicola from Thamakan, x 4. 

 Fig. 7. — Operculum of the subspecies lacustris (magnified). 



Hydrobioides physcus, sp. no v. 



Figs. 8, 8a. — Shell from the Inle Lake. Length 7 mm. 

 Fig. 9. — Operculum of the same shell. 



