172 76 
down the anterior side and one broader radiating depression down the posterior 
side. It is almost circular in outline, but the posterior end is rather straightly 
truncated. The surface is covered with numerous close-set, regularly-arranged, fine, 
slender liree, which towards the lunule and hinder dorsal slope are more elevated. 
The lunule is rather deep and large, cordiform, smooth. The area is long and 
narrow. The beaks are small, sharp, well-curved over the lunule. The valves are 
covered (in quite fresh individuals) with an extremely thin epidermis, which under 
the lens exhibits a few fine radiating lines. In both valves the lateral teeth are 
well-developed, the posterior being the smaller, and the cardinal teeth are obsolete; 
the internal ligament is in a groove just within the dorsal margin. The interior 
of the valves is of a dull white colour and under the lens is seen to have fine, 
faint, radiating lines. 
Long. 75 mm., alt. 8 mm., crass. 5 mm. 
The strand off the mangrove at the station on Koh Chang (54). 
The peculiar depressions down the anterior side are characteristic of this 
species. The shell varies rather considerably in form; especially in older specimens 
it has a tendency to be drawn obliquely towards the anterior end, so that the 
umbones may even be situated far back in the hinder half of the shell, while in 
other individuals they are situated in the middle of the length of the shell. I have 
named this new species after Mr. W.H. Dati of Washington to whom malacological 
science owes so many valuable papers, and who has also revised the genus Lucina. 
Lucina (Phacoides) pisum, Reeve. 
Lucina pisum, Revver, Conchol. icon., VI, 1850, Lucina, Sp. 66 (non Lucina pisum, Philippi! = Divaricella 
perparvula, Dall”). 
—  (C€odakia) pisum, Reeve, Eva. Smiru, Lamellibranchiata of the Challenger Exped., p. 181. 
Parvilucina eucosmia, Dati, Synopsis of the Lucinacea, 1901, p. 806. 
Between Koh Mesan and Cape Liant, 5—9 fathoms, sand ('/2). Between Koh 
Riot and Koh Mesan, 3—5 fathoms, sand (?/2). S. of Koh Chuen, soft clay and 
mud (1/2). Gulf of Rayong, 7—10 fathoms, sand, mud, and shells (‘/2). S. of Koh 
Samit, 14—20 fathoms, mud (1 + 7/2). Off Tung Kaben, 6 fathoms, mud mixed 
with sand ('/2). Koh Chang, between stones, very low tide (1). West coast of Koh 
Chang, 10 fathoms, mud (‘/2), N. of Koh Kahdat, 4—5 fathoms, coarse sand ('/2). 
Koh Kahdat, on the strand (about 2°°/2 specimens). S. of Koh Kahdat, 8—10 fathoms, 
mud (‘/2). Between Koh Kut and Koh Kahdat, 10 fathoms, shells (*°/:). W. of Koh 
Kut, 18 fathoms, mud (9). 
Long. 2—6 mm. 
Distribution: — Singapore (Cumina; Sy. Gap, 2—3 fathoms). Mergui Isls. 
(E. vy. Marrens), Madras (Metviti & SranpEN), Gulf of Manaar (THuRSsTON). — S. of 
New Guinea (“CHALLENGER”), Port Essington (Brit. Mus.). 
1 Abbild. u. Beschr. neuer od. wen. gek. Conchyl., III, 1850, p. 105. 
* Synopsis of the Lucinacea. Wash, 1901, p. 815. 
