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night they crawl about on the surface of the bottom — as I have 
also observed in other places (e. g. Hawaii). The diver, who proved 
to be also an expert collector here on the flåts, maintained that 
the Brissus would come out only when quite dark; even the moon 
light it did not like! 
These flåts otherwise are conspicuous through being covered to 
a great extent by small hilis looking very much like mole casts; 
by low water they look very picturesque, small ponds of clear water 
remaining between them, in which they are reflected. That these 
hilis are due to the action of some sort of animal is evident — 
but which sort, I have not been able to make quite sure. The idea 
that they might be due to Enteropneusts, which I have in other 
places seen to produce something the like, though on a smaller 
scale, had at once to be discarded. Digging in the mounds and 
following the holes did not result in finding the originator with 
certainty. Not rarely a large Sipunculid, footlong, red, somewhat 
thicker than a finger, was found therein, and the diver insisted on 
the mounds being made by this animal. I am, however, more in- 
clined to think that they are formed by a Thalassina, which Decapod 
is well known to make huge mounds, where it lives; a single 
specimen of this form was found here, it being thus certain that 
it does occur here. The big Squilla’s, which also occur here, living 
in holes in the ground, do not make mounds over their holes. 
A very curious feature was observed on these mounds, viz. 
a more or less radiate arrangement of the particles on the top. 
That this is due to the action of the waves is beyond doubt; they 
form on the freshly thrown out material wave-lines, sorting the 
material according to weight, the lighter grains of white coral coming 
then to lie between the elevated lines of the heavier, black volcanic 
sand particles; a doser inspection shows that the wave-lines are at 
a right angle to the dominating direction of the wind, as should be 
expected. Similar Thalassina(?)-csis{s, were also observed in great num- 
bers on the sandy flat at the S. coast of Doe Roa, at the Kei Islands. 
The flat at Lontor is in its inner part strewn with huge, black 
volcanic bombs, the ground between these larger stones being, as 
it were, paved with small, smooth, black stones. This part — an 
area of several hectares — which is covered by the water only at the 
highest tide, is the home of a small crab of the Gelasimus-group; 
