In the Nicobar Islands of the Indian Ocean a well-developed example of vigesimal numeration is found. The inhabitants of these islands are so low in the scale of civilization that a definite numeral system of any kind is a source of some surprise. Their neighbours, the Andaman Islanders, it will be remembered, have but two numerals at their command; their intelligence does not seem in any way inferior to that of the Nicobar tribes, and one is at a loss to account for the superior development of the number sense in the case of the latter. The intercourse of the coast tribes with traders might furnish an explanation of the difficulty were it not for the fact that the numeration of the inland tribes is quite as well developed as that of the coast tribes; and as the former never come in contact with traders and never engage in barter of any kind except in the most limited way, the conclusion seems inevitable that this is merely one of the phenomena of mental development among savage races for which we have at present no adequate explanation. The principal numerals of the inland and of the coast tribes are:[356] INLAND TRIBES COAST TRIBES 10. teya. 10. sham. 20. heng-inai. 20. heang-inai. 30. heng-inai-tain 30. heang-inai-tanai = 20 + 5 (couples). = 20 + 5 (couples). 40. au-inai = 2 x 20. 40. an-inai = 2 x 20. 100. tain-inai = 5 x 20. 100. tanai-inai = 5 x 20. 200. teya-inai = 10 x 20. 200. sham-inai = 10 x 20. 300. teya-tain-inai 300. heang-tanai-inai = (10 + 5) x 20. = (10 + 5) 20. 400. heng-teo. 400. heang-momchiama.