184 88 
Montacuta (Tellimya) rudis n. sp. 
(Pl. III, Figs. 33—34). 
This shell, which is oblong-ovate, is, especially in the anterior half, somewhat 
ventricose; it is white and rather thin. Anteriorly the shell is truncated, but 
posteriorly it is pointed. The ventral side is straight; across the middle from the 
umbones to the ventral margin the valves are somewhat depressed. The umbones 
are situated in the anterior half of the shell, the apices are glossy, smooth and 
pointed. Upon the surface, which is covered with a yellowish epidermis, the rough 
and coarse concentric lines of growth may be seen; in addition to these are distri- 
buted, over the whole surface, numerous fine or coarse grains and tubercles which 
make the valve-surface peculiarly rough and uneven. The interior of the valves 
is glossy, the left valve has in it, separated from the upper margin by a groove, 
two diverging, triangular, compressed, acute cardinal teeth, between which are 
placed the ligament and the ossicle; these fit into a triangular pit just below the 
apex of the right valve; close to this pit and directly upon the upper margin there 
is on both sides in the right valve an oblong lateral fold, which fits into the 
corresponding groove above the cardinal teeth of the left valve. The muscle im- 
pressions are large and very conspicuous. 
Long. 7°5 mm., alt. 5 mm., crass. 3 mm. 
The north side of Koh Chang, 12 fathoms, in old coral blocks (1). 
The peculiar surface is characteristic of this species, which lives in holes. in 
coral blocks and which therefore, as is the case with all the forms which are found 
in such localities, is subject to changes in form according to the locality which it 
may chance to inhabit. 
Lepton sp. 
A single, somewhat damaged, left valve of a Lepton was taken in the sound 
of Koh Chang, in 3—5 fathoms, on a soft muddy bottom; it should be placed near 
to L. trigonale, Tait, but differs from it. In the British Museum there is a specimen 
of an undetermined Lepton from Port Lincoln which exactly agrees with my shell 
from the Gulf of Siam. 
Fam. Galeommidae. 
Galeomma angusta, Desh. 
Galeomma angusla, DresHayes, Proc. Zool. Soc. London, XXIII, 1855, p. 170, No. 7. 
— — — Sowerby, Thesaurus Conchyl., Ill, p. 174, No. 8, pl. 234, fig. 10. 
Sowersy in Reeve, Conchol. icon., vol. 19, Galeomma, Sp. 3. 
Coast of Lem Ngob, low tide, stones (150 specimens). Gulf at the south end 
of Koh Chang (7). Koh Chang, very low tide, stones (5). North end of Koh Chang 
1 fathom, old coral blocks (2). 
