1918. J N, Annandale : Molluscs of the Inle Lake. 109 



We found a small but constant series of living specimens near the 

 shore-line of the marginal zone of the Inle Lake at Fort Stedman. They 

 were living amidst much decaying vegetation matter in conditions 

 which favoured the formation of peat. 



Phase D. 



The shell is thicker than that of phase C and has coarser growth- 

 lines. The sutures are sinuous but not very oblique and the whorls 

 of the spire swollen. The apical whorl is very small and almost 

 globular. The body-whorl is contracted and the whole shell is narrow. 

 The aperture is also narrow but less contracted posteriorly than in 

 phase B. The columellar callus is less well developed than in the other 

 phases. The size is much reduced, as the following measurements will 

 show : — 



mm. 

 Length ... ... ... ... ... ... 6-5 



Greatest breadth ... ... ... ... ... 2-75 



Length of aperture ... ... ... ... 4-5 



Greatest breadth of aperture ... ... ... ... 2 



I only know this phase from two dead shells dredged from the bottom 

 in about 7 feet of water in the central region of the Inle Lake. There 

 is no doubt that the animal lived approximately in the place where 

 the shells were found, for one of the specimens has been perforated 

 (see figure) and must have sunk at once into the bottom of the lake. 

 The phase is of great interest in that, while clearly a member of the 

 same series as the other phases, it leads on towards the next species, 

 which I have called, for other reasons, L. mimetica. 



Considering all these phases together we may be sure of the following 

 facts : — 



{i) They may be regarded conventionally as the links in a chain 

 of evolution in which the tendency is towards a narrow- 

 ing of the shell and of its aperture and a reduction of 

 the spire. 

 {ii) Evolution has affected the buccal armature less than it has 

 affected the shell and though there is a distinct break in 

 shell-form between phase C and the Tibetan species with 

 which I have associated the phases, the radula and jaw 

 are practically identical. 



I will discuss the significance of these facts when dealing with varia- 

 tion among the shells of the Inle and He-Ho basins {v. p. 151). 



Limnaea mimetica, sp. no v. 

 Plate X, figs. 9, 9a ; plate xi, fig. 4. 



The shell is very small and delicate, transparent, colourless or tinged 

 with yellow, imperforate, rimate, narrow, subcylindrical. It has tlie 

 lines of growth well marked but not coarse. The spire, which is set' 

 on the body- whorl at a slight angle, is blunt and short, but so obliquely 

 spiral that it appears twice as long in the dorsal as it does in the 



