I92I.] 



Manipur Molluscs. 



571 



but irregularly sculptured and may be described as coarsely 

 malleated. The shells are narrow, with long spires but not of ex- 

 treme type in shell- form. They are rather small. The animals 

 in these shells were very pale in colour. 



Two abnormal specimens may now be described. They were 

 found together in a bed of Potainogelon at the point at which the 

 main outflow leaves the Loktak Lake. One only differed exter- 

 nally from the majority found with it in its larger size. It is 

 numbered A (i) in the table of measurements. We may note that 

 its size was large only \\\ comparison to other individuals found 

 with it, for nmch larger individuals are common at some places. 

 On dissection it was found that the body-cavity of this individual 

 was occupied by a contorted mass of elongate filiform Trematode 

 sporocysts, which completely surrounded the upper part of the 

 genital system. All the genital glands were crowded together in 

 a degenerate mass, while the female ducts could not be traced. 

 The lower part of the vas deferens and muscular penis-sac with 

 its retractor muscles were, however, intact. 



The other abnormal specimen (pi VII, fig. 3) was peculiar in 

 shell-form. It was remarkable for the very small size of its spire 

 and the relatively great length of the aperture ot the shell. The 

 interesting feature of this abnormality (or ? mutation) is that the 

 peculiarities in shell-form are among those commonly found in 

 lacustrine species and phases of the genus. The shell, however, 

 had not all the characteristics of such forms as it was no paler, 

 thinner or smaller than those taken with it. 



Measurements of Shells (in millimetres) 



A. .\ small channel south of Thanga Island with bed of clean Potamogetoii 



abnormal specimens; ( i) is the large specimen and (2) the shon- 

 spired form. 



B. Same locality (normal individual). 



C. Swamp at Thanga Island m the Loktat Lake. 



D. Small muddy bathing pools Thanga Island. 



E. Potsengbam, northern end of the laUe. 

 ¥. Amingaon, near Gauhati, .\ssam. 



