236 ZOOLOGISCHE MEDEDEELINGEN — DEEL VI. 



About the question of distribution of animals over and their origin 

 in the small islands along the west coast of Sumatra different opinions 

 exist. The reptile-fauna is rather well known, since some large collec- 

 tions have been made during the last twenty years, so that I will try to 

 give my conclusion on some points with regard to that group of animals. 



Werner ] ) gives as his opinion that the islands got their fauna from 

 Sumatra with this restriction, that each island is inhabited by those rep- 

 tiles which live in a part of Sumatra next to the island, so that the islands 

 between them show very different species. This fact may be explained 

 by the circumstance that these species have a very restricted distribu- 

 tion in Sumatra. Other authors agree to this hypothesis. Barbour 2 ) 

 concludes that the groups of islands have never been united and 

 have never formed a bridge between Java and continental India 

 across the Nicobars without Sumatra, because their reptile-fauna has too 

 much resemblance to that of Sumatra. Yan Kampen 3 ) has the same 

 explanation with regard to the batrachians. Barbour supposes that the 

 different groups of islands have been in connection with Sumatra, inde- 

 pendently one from the other, so that they got their reptiles and 

 batrachians from that small part of Sumatra that corresponds with the 

 bridge. Simalur was connected with the mainland across the Banjak 

 Islands ; Mas had a direct connection with the region of Sibolga ; the 

 Mentawei Islands were united and connected with Sumatra by means of 

 the Batu Islands, so that three peninsulae existed, a north-western, a 

 western and a southwestern one. A support for this hypothesis could be 

 found in the results of the soundings of the Yaldivia. The sea north 

 and south of Nias is deeper than the water between that island and 

 the mainland ; the Mentawei Islands are separated from Sumatra by a sea 

 of 200 — 2000 M. depth, whereas the water between Siberut and the three 

 largest Batu Islands is not deeper than 6 — 150 fths. 



The big collections of reptiles from Nias and Simalur and some ani- 

 mals caught in Siberut made it possible for me to say something about 

 their distribution. The greater part of these reptiles are sumatran forms, 

 so that I agree to the fact that Sumatra has given the inhabitants 

 to the small groups of islands. But I think that the islands have been 

 united because of the occurrence of two lizards: Gonatodes hamlia- 

 nus and Lygosoma relictwm. The first is a gecko living in S. India, 

 Ceylon, Simalur, Pulu Babi, Nias, Sipora and Engano; the second a 



1) Zool. Jahrb. Sysi. Bd. XIII 1900, p. 507. 



2) Mem. Mus. Comp. Zool. Harv. Coll. Vol. XLIV n°. 1 1912. 



3) Notes Leyden Mus. Vol. XXXVI 1914, p. 262.. 



