X UPPER BURMAH AND PEGU 305 



and Aracan, while essentially a part of the Indian province, 

 contains several Siamese genera which are not found in India 

 proper, as well as several which are at present peculiar. 

 Amongst the former category are, of Helicidae, a single repre- 

 sentative each of the genera Camaena (Siamese and Chinese) and 

 Aegista (Chinese). Influence of the same kind is seen in the 

 increased numbers of Plectopylis (14 sp.) and Plectotroph (5 sp.), 

 of Olausilia (10 sp.) and Amphidromus (5 sp.), 

 and of the large tubed operculates (11 sp. in all). 

 Sesara and Sopliina among the Naninidae are 

 strange to India, while Hyalimax is common only 

 to the Andamans, Nicobars, and Mascarene Is. 

 Hypselo stoma (Fig. 202, A) is a most remarkable 

 genus of the Pupidae, reminding one of Anostoma 

 of the New World. It is peculiar to the peninsula, 

 but for one species in the Philippines. Among 

 the Pupinidae, we have the peculiar Maphaulus 

 and Hyhocystis (Fig. 205), a very remarkable form, 

 of which another species occurs at Perak. Two ^^'rystis~gravida 

 Helicina mark the most westward extension of Bens. Young 

 the genus on the mainland. In the extreme 

 north of Upper Burmah, Indian and Chinese forms intermingle. 

 The Burmese district, together with the Indian and Siamese 

 provinces, is pre-eminently the home of a group of Mollusca, 

 originally of marine origin, which have permanently habituated 

 themselves to a brackish or fresh-water existence. They belong 

 to widely different families, and even Orders. Besides Cremno- 

 conchus mentioned above, we have, among the bivalves, Novacu- 

 lina, a Sole^i living in fresh water in the Ganges, Irawadi, and 

 Tenasserim estuaries ; Scaphula^ an Arca^ one species of which 

 occurs in the Gauges hundreds of miles above the tideway (see 

 Fig. 9, p. 14) ; and Martesia, a Pholas from the Irawadi Delta. 

 Clea (which also occurs in Java and Sumatra) is probably an 

 estuarine Cominella ; a Tectura has earned the name fluminalis 

 from its exclusive residence in the Irawadi R.; Iravadia is 

 probably a Rissoina of similar habits, occurring from Ceylon 

 round to Hong-Kong ; Brotia is a Qerithhim from an affluent of 

 the River Salwin, and Caiiidia is a Nassa^ occurring in the 

 embouchures of rivers from India to Borneo. Nowhere else in 

 the world is there such a collection — not exhausted by this list 



VOL. Ill X 



