1921.J B. Prashad : Swnatran Molluscs. 497 



There is a single specimen in the Sumatran collection which is 

 referrable to this genus. Brot described it from Sumatra and it 

 has not been found anywhere else. 



Clea bocki, Brot. 



1881. Clea Bockii, Brot, Jonrii. Conchyliol. XXIX, pp. 159. i6o, pi. 

 1895. Clea Rockii, Smith, Proc. Malacol. Soc. London, L, p. 253. 



I assign to this species a single specimen obtained in the 

 mangrove-swamps at Belawan, Deh. The mouth is slightly broad- 

 er and the bodj'-whorl a little larger than in Brot's figure, but 

 these differences are probably of the nature of individual varia- 

 tions. The entire spire except for the penultimate whorl has dis- 

 appeared and the specimen is in poor condition, but the charac- 

 teristic sculpture on the shell is well preserved. 



The occurrence of a member of the genus Clea in estuariiie 

 areas is worthy of note, as the genus is essentially a fresh- water 

 one. 



Family Neritidae. 



Genus Ncritina, Lam. 



Subgenus Neripteron, Recluz (= Auriculatae, v. Martens). 



The only species in the Sumatran collection I assign to this 

 subgenus is the new form described below as N. simoni. It is a 

 very interesting species, in that it shows definite relationships 

 between the subgenera Neripteron and Dostia, but clearly belongs 

 to the first sub-genus. 



Neritina simoni, Prashad (sp. nov.). 



(Plate xiv, figs. 13, 14). 



The shell of this species is suborbiculate-ovate, with the 

 posterior margin regularly curved. Its lateral profile is somewhat 

 semicircular, much more arched on the anterior than near the pos- 

 terior margin. The spire is short and distinctly lateral, but 

 obliquely turned inwards ; only a small part of it is visible in 

 ventral view. The columellar area is provided with a short 

 auricle on the upper side ; on the lower side the auricle is not 

 well developed. The columellar plate is very broad, extending to 

 a little more than half way across the ventral surface ; it is greatly 

 depressed inwards towards the true mouth. The free margin of 

 the columellar plate is slightly but regularl}- curved, and is 

 finely crenulate. The periostracum is dull black, and has fine 

 concentric striations on its surface ; the columellar plate is dull 

 olivaceous with a tinge of orange in some places ; the mouth is 

 rather dusky and the operculum is dark brownish with a light 

 orange border. 



