96 DR. NELSON ANNANDALE ON THE 



free on the bottotn, the objects to which tliey hal been attached having 

 completely perished. 



The number of molluscs found living in this part of the lake- 

 system was extremeljf small. The g'^nera represented in my collection 

 are : — Marghiella ( by an apparently undeseribed species ). Ca$sidula, 

 Potamides, Faunus, Littorina, Conradia, Sicnoilnjfii and Neriiina among 

 the Gastropols, and Osirea, Maliola, Area, Scaph-if'a, Splnnia, Xylolrija, 

 Theora and Anatina among the Lamellibranchs. Many of these genera 

 ( for example Cassidida, Potamides, Neritina, Osirea and Area ) are re- 

 presented by species of very wide Oriental distribution that are found 

 in aln70st every estuary between that of the Indus and that of the 

 Yangtse-Kiang. It is remarkable that the si>ecies of the other 

 Laniellibranch genera are in most cases totally difiVrent from those 

 recorded or described by Lynge^ from shallow water on the other side 

 of the Gulf of Siam. The only species that I can assign with cer- 

 tainty to one found also in the inner lake is the Scaplmla. Some 

 very small specimens of Modiola may belong to M. ecansi, but most of 

 them seem rather to be the young of M. undidata, a species common in 

 Indian estuaries and lagoons but originally described from the Philip- 

 pines. 



Crustaeea. Most of the crabs of the outer lake belong to the 



family Grapsidae ( whicli supplies a very large proportion of the species 



that haunt the estuaries of Oriental rivers ) and are either shore-crabs 



or amphibious in habits. Some of these ( such as Varana Uttorata ) 



Jiave a very wide range on Indo-Pacific coasts, but a few seem to be, 



so far as we know at present, peculiar to the Gulf of Siam. The 



uumber of species, however, that are identical with those recorded by 



Miss Rathbun 2 from shallow water on the other side of the Gulf is not, 



excepting forms of wide range, so large as might be expected. The 



running-crabs ( O.xypodidae ), so characteristic of sea beaches in the 



tropics, are represented inside the mouth of the lake by but a few 



species and other families also are poorly represented. Among the 



' T Lyiigo, " The Danish Expedition to Siam 189i)-l'J00. IV. Marine 



Jjamellihrancliiata." Det /u/l, Vklensk. Selsk-. Skr. h'obndiKrn, 7 Raekke, nat. 

 og uial., Afd. V, 3 ( I'JO',)).' 



2. Rathbun, "Tlic Danish Expoditinn to Siam, 1«'J!)-1900. V. Bra- 

 chyura". Det KgL Vidtnuk. Schk. ^kr. Kobenharn, 7 KnoUko, naf. og math., 

 Afd. V, I (1010). 



JOUKN. NAT. IJIST. SOC. SIAM. 



