BARBADOS-ANTIGUA EXPEDITION 191 
voured by the urchins. It seems evident, therefore, that these 
Protozoa furnish a considerable portion of the nutriment: which 
sustains the life of these burrowing sea-urchins. It was a sur- 
prise to me, however, to find this apparent proof that these deli- 
eate protozoans could live under this firmly compacted layer of 
sand, and we are still confronted with the question,—what do 
they live on, under an almost ideal sand-filter? This sand is 
almost entirely calcareous and thus furnishes an abundance of 
the carbonate of lime which contributes perhaps ninety per cent 
of the material of which these sea-urchins are made. Of course 
it may be said that they live on the sarcode from other protozoa, 
or even disintegrating members of their own kind, all of which 
reminds one of the celebrated commercial enterprise known as 
the ‘‘Cat and Rat Farm,’’ the owners of which were said to be 
realizing huge profits by feeding the rats to the cats, skinning 
the latter, disposing of the pelts for cash and then feeding the 
bodies of the defunct cats to the rats, and so ad wfimtum. 
Possibly, these urchins are nocturnal and come to the surface 
to feed in darkness. In that case the difficulties discussed above 
will disappear. 
There were, as already indicated, two species of the curious 
forms. One was apparently Hchineis semilunaris, which was | 
also secured at Barbados. It was smaller than the other, but 
much like it in shape and color. The test is ovoid and the am- 
bulacra are not at all sunken, but each appears as a perfectly 
evident double line of pores extending almost paralle! around 
the test to the actinal surface. The mouth and anus were close 
together and both ventral. The tests were exceedingly fragile 
and had to be packed carefully in cotton for transportation. 
The other species agrees very. well with the excellent photo- 
graphs and description of Brissus wnicolor found in Alexander 
Agassiz’s splendid monograph ‘‘ Revision of the Kchini.’’ Al- 
though more recent writers may shuffle the names ad libitum, it 
is doubtful if any better work will be done on this group than is 
found here. The specimens collected by us at Antigua were 
none of them so large as those figured by Agassiz; but they 
agreed very closely in detail. A typical one is ovoid in form, 
the posterior end somewhat elevated and truncate. It is 5.3 em, 
in length, 3.8 em. in diameter, and 3.2 cm. in height. The 
