presideijt's address. 255 



to their existence. Thus they are to be seen at their best development 

 in the rainy season, and I believe these moist conditions have played 

 no small part in their evolution, by the stimulus they have given to the 

 expansion of the shell-lobes. When kept in captivity they do not live 

 long- ; the mantle shrivels up and exposes the shell more and more 

 daily, the bright and glistening surface of the body becomes first dull 

 and then covered with fungoid growth and sores, under which the 

 animal succumbs. 



There is yet another section of mollusca with thin, poorly developed 

 shells, which are concealed, like those of the genera I have already 

 .spoken of, beneath ample shell-lobes. This section is represented by 

 the genus Burgella, first known as a native of Tenasserim, and it 

 possesses very distinctive characteristics of its own. Its principal 

 points of divergence from Girasia and its allies are found in the feeble, 

 straight jaw, and large broad radula, with minute central tooth and 

 an immense number of serrated teeth, all similar in shape, in each 

 row, while the generative organs are simple. Since Mr. "VV. T. 

 Elanford described the genus, species have been discovered in the 

 Khasi Hills, in the Assam Plain, one in the Andamans, one in 

 Peninsular India, and one far away in Porneo. It has thus a very 

 remarkable range. No close relationsliip has yet been found between 

 it and other forms ; save perhaps with Iialiella, which it resembles in 

 the form of the lateral teeth of the radula. Durgella, therefore, may 

 perhaps represent a primitive race that has nearly died out, but it is 

 yet possible that further research may reveal other forms with which 

 it can be associated. 



Kaliella has a very interesting range. Starting with Kashmir, it is 

 found along the whole of Northern India, at or near the base of the 

 hills, in the plains, in Assam, Purma, Southern India, and Ceylon, 

 and I have even received it from Madagascar. Sitala is hardly less 

 circumscribed in its range. The two genera are in certain points allied 

 anatomically, but it is noteworthy that Sitala, as shown by Stoliczka, 

 has one section, represented by S. infula, in which the amatorial organ 

 is absent, and the teeth of the radula are very numerous. 



I have now brought to ^-our notice the majority of Zonitoid genera 

 the animals of whicli have been examined. 



Microci/stina is an Andaman form, and if the shell can be trusted 

 occurs in Ceylon and Pornco,but better material from these lands 

 must be worked over again. 



Sophitia, described by Stoliczka, is a very distinct genus, peculiarly 

 local, confined to Tenasserim and southwards to the Malay Peninsula, 

 and not extending to the north. Xesta is a well-marked Malayan group, 

 so is JRhysota. Parmarion, Ificropannarion. and Damayantia, Simroth 

 has shown to be genera very distinctive in themselves, and inhabitants 

 of Java and other islands, as well as Porneo. In Microcystina, numerous 

 small forms have been placed, apparently because there was no other 

 genus open to receive them ; it no doubt will break up into several 

 very distinct divisions, and leave Microcystina proper to the islands of 

 the Pacific. You will, I think, agree with me that this investigation 

 may be said to have only been begun. There is a vast amount of work 



