304 



CEYLON AND SOUTHERN INDIA 



CHAP. 



decisively separating that island from India, Burmah, and 

 Siam, forms a most interesting problem in the history of dis- 

 tribution. Eurystoma^ with a single species (^E. vittata MiilL), 

 is also peculiar. 



As usual when Helix gains ascendancy, the Naninidae retro- 

 gress. Durgella^ Austenia^ and Girasia are absent altogether, 

 while Macrochlamys^ Sitala^ Kaliella^ etc., are present in greatly 

 diminished numbers. The sub-genus Beddomea is peculiar, a 

 form directly related to Amphidromus (Siam and Malacca). 

 The fresh-water operculate Philopotamis is peculiar, but for one 



Fig. 204. — Helix {Accu- 

 vus) Waltoni'Re&\e, 

 Ceylon, showing em- 

 bryonic shell {emh). 



species found in Sumatra ; while Tanalia is quite peculiar. But 

 the forms which, next to the Helices^ most emphasise the separa- 

 tion of the Cingalese district are the land operculates. There 

 are eleven genera or subgenera of land operculates which do not 

 occur in the rest of India proper. Two (^Aulopoma and Oataulus) 

 are quite peculiar, while the other nine are represented in 

 Burmah, Siam, and the Malay islands, but not in India. On 

 the other hand, Diplommatlna and Alycaeus^ so profusely abun- 

 dant in India, have not yet been discovered in Ceylon. Among 

 the slugs, Tennentia is a peculiar genus, whose nearest relation 

 occurs in the Seychelles. 



G-enera and Subgenera occurring in the Cingalese District^ but 

 not in JV. and Central India 



1 



Streptaxis 



Beddomea 



Craspedotropis 



Mychopoma 



Tennentia 



Philopotamis 



Pterocyclus 



Cataulus 



Acavus 



Tanalia 



Aulopoma 



Nicida 



Eurystoma 



Theobaldius 



Ditropis 



Opisthostoma 



Gorilla 



Leptopomoides 



Cyathopoma 





The district consisting of Upper Burmah, Pegu, Tenasserim, 



