3o6 



THE ANDAAIANS AND NICOBARS 



— of marine forms caught in process of habituation to a fresh- 

 water or even a land existence. 



The Andaman and Nicohar Islands possess no peculiar features 

 in their land MoUusca. They are closely related to the adjacent 

 coasts of Lower Burmah. AmjihidroiJius (2 sp.) occurs in the 

 Andamans alone, and Clavsilia (2 sp.) in the Nicohars alone, 

 while Hyalimax occurs in both groups. A remarkable Helix 

 (codonodcs For.) from the Nicoljars appears to find its nearest 

 relations in the isolated group from Busuanga and Miudoro (p. 

 315). Land operculates are aljundant, in the Nicobars actually 

 outnumbering the pulmonates (28 to 22). Helicina and Om- 

 phalotrojns, genera characteristic of small islands, are found on 

 both groups. 



(/)) The Siamese Province includes the area occupied l)y the 

 districts known as Siam, Laos, Cambodia, Cochin China, Annam, 

 and Tonquin. Along the whole of its northern frontier, the 

 zoological is no more than a political boundary, while on the 

 east the mountain ranges which part Siam from Pegu and 

 Tenasserim are not of sufficient height to offer any effective 

 barrier to distribution. The province is accordingly qualified to 

 a considerable extent by Indian and Chinese elements. 



Streptaxis is, but for three Ennea, the sole representative of 

 the carnivorous genera, and attains its maximum in the Old 

 World. Partly owing to Chinese infiuence, the Helicidae, with 

 11 genera and 46 species, begin to regain their position as 

 compared with the JSTaninidae (12 genera, 54 species). Of the 

 Helicidae, Acusta and Hadra appear now for the first time, and, 

 with Plectotrojns, Stegodera, and CUmsilia, form a marked 



Chinese element. Amjjhidromus, 

 with 33 species, is the most char- 

 acteristic land pulmonate. Several 

 genera, whose nucleus of distribu- 

 tion lies among the islands farther 

 east, appear to have penetrated as 

 far as these coasts. Such are Chlo- 

 ritis, Camaena, and Ohhina among 

 the Helicidae, Trochomorpha, and, 

 of the operculates, Helicina. 



Land operculates are very richly 

 developed. In all, there are 17 genera and 104 species known. 



Fig. 206. — Cycloplwrus siamensis 

 Sowb., Siam. 



