576 Records of the Indian Museum. [Vol. XXII, 



Phase I (Intermediate) (pi. VIII, figs. 2-5).— This phase was 

 found in a fairly large swampy pond, evidently connected with a 

 small stream in the rainy season, at Dimapur and in several 

 ponds at Imphal, Manipur, in February and March, T920. The 

 ponds were well supplied with submerged aquatic vegetation 

 but the molluscs were most abundant (at Dimapur) in a half isol- 

 ated pool with no vegetation of the kind and evidently forming 

 part of the bed of a sluggish stream for part of the year. They 

 were pairing and ovipositing in March, i.e. some months before it 

 is probable that the stream would be running. In these condi- 

 tions greater individual variability occurred than among individuals 

 living (at Imphal) amongst dense vegetation in permanent ponds. 

 Imphal (2,600 ft.) is probably situated at a somewhat higher altitude 

 than Dimapur. 



This phase, as we have pointed out above, is a connecting 

 link between L. ovnlior and L. andersoniana. Many individuals 

 of it come rather close to the former species, but all are much 

 smaller, have the body- whorl less inflated and the penultimate 

 whorl rather broader. The sculpture is also less coarse and more 

 regular. The shell is usually broader than in the next phase and 

 capable of growing larger. 



Phase II (Pond Phase) (pi. VIII, fig. i).— This is the jorma 

 typica of the species and has been found both in Yunnan (in 

 unknown circumstances) and also in ponds full of submerged 

 vegetation in the vSouthern vShan States, at altitudes of 3 000 feet 

 or over. The shell is narrower and as a rule more fragile than in 

 the former phase. Similar but slightly broader specimens occur 

 in pools at Imphal. 



Phase III (vStream Phase).— Specimens have been lomid in 

 muddy spots at the edge of streams in the Southern Shan States 

 and in the Manipur Valley, also in rice-fields irrigated from the 

 same streams ; and in unknown circumstances in Yunnan, Kashgar 

 and Nepal at altitudes between 2,600 and 5,000 feet. They occur, 

 often in large numbers on bare mud in an entire absence of 

 phanerogamic vegetation. The shell is considerably narrower 

 and usually smaller than in the preceding phases, rather thicker 

 and duller in colour. This phase has been described b>- Preston 

 under the name Liinnaeo simulans 



Phase IV (Hill Stre.\m Phase (pi. VIII, fig. 6).— Specimens 

 of this extreme phase were collected in a hill- stream near Potseng- 

 baro on the west side of the Manipur Valley. The stream has a 

 rapid current, very clear water and a bottom of small ptbbles and 

 stones. The specimens of Limnaea were found attached to the 

 pebbles in a shady area along the banks. The shell of these 

 specimens is still narrower and more elongate than in the preced- 

 ing phase, with the spire smaller and less legular, and the callus 

 less indistinctly marked; the mouth is narrower and more pointed. 

 The shell itself is paler and more polished. 



