Introduction. 



Wur knowledge of the marine Lamellibranchiala of the Gulf of Siam was for 

 a long time very limited. Thus, when Professor Ed. v. Martens, in 1860, puhlislicd 

 his paper "On the Mollusca of Siam" in the "Proceedings of the Zool. Society 

 of London," he mentioned in it only 7 species of marine Lamellibrnnchiata. Nor 

 was our knowledge of the fauna enlarged until L. Morlet described Mr. Pavie's 

 collections in the "Journal de Conchyliologie," 1889; bul in 1891, when Paul 

 Fischer published his "Catalogue el distribution géograph. d. Mollusques terrestres, 

 fluvialiles el marins d'une partie de l'Indo Chine" ' lie was able lo record 72 species 

 of marine Lamellibranchiata from the Gulf of Siam, and this number has been in- 

 creased to 85 species by Pavie's new collections, which Crosse & Fischer, in 1892, 

 described in the "Journal de Conchyliologie." By Dr. Th. Mortensen's thorough 

 and excellent dredgings and collections from the eastern part of the Gulf of Siam 

 during the years 1899 — 1900, the number of known species of Lamellibranchiala 

 from that place has now been increased to 379 species. But the fauna is without doubt 

 slill far from exhausted by this last addition, because the Danish Expedition dredged 

 only in the northern and eastern parts of the gulf, and only down to a depth of 

 about 35 fathoms. The Mollusc fauna in the western part and also in the deeper 

 parts in the middle of the gulf is still unknown. Il is true that the "Skeat-Expedi- 

 lion" has made collections on the Malacca side of the gulf, but the Mollusca of 

 these collections have not yet been worked out. Thus, as it is only the littoral 

 fauna of a part of the gulf which is known, it must be understood that the present 

 list is only the beginning of a complete list of the species occurring in the gulf. 

 Though it may be supposed that the littoral fauna of the northern and eastern 

 parts of the gulf is now almost completely known, yet it is probable Ihal the fauna 

 of the western side of the Gulf of Siam is richer, and contains many species which 

 have not hitherto been taken on the eastern side. This is owing to the fact that 

 the water on the Malacca side is much purer and fresher than in the eastern part, 

 where the outlets of the numerous rivers make the sea-water foul and muddy and 

 also less saline.^ 



' Bulletin Soc. Hist. Nat. d'Autun. IV, 1891, pp. 87-276. 



- Cf. Th. MoRTiiNSEN, "The Danish E.\pedition to Siam, 1899— 190(1. Results of tlie zoological 

 Collections." Kgl. Danske Vidensk. Selsk. Skrifter, 6. R. Naturv, og matliem. Afd. XII, 2, 1902, pp. 155—57. 



