4 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 
Of particular importance are Hemiphormosoma paucispinum and 
Paraphormosoma alternans, both representing new generic types re- 
lated to Phormosoma and necessitating the establishment of a sepa- 
rate subfamily, the Phormosominae, for this group of genera, the 
other genera forming another subfamily, the Asthenosominae. A 
third subfamily, the Kamptosominae, is not represented in the pres- 
ent collection. 
A rather extraordinary fact relating to the biology of the deep-sea 
echinothurids was substantiated by a study of this material, together 
with that collected by myself south of Mindanao in 1914, and that is, 
that most of them are plant-feeders. The contents of their alimen- 
tary canal consists almost exclusively of small bits of plants, looking, 
indeed, like chaff; and it is not algae, but the remains of land plants. 
This sounds rather paradoxical—deep-sea animals feeding on land 
plants! But the explanation is not difficult. In areas with a luxu- 
rient tropical vegetation, like the Philippines, a large quantity of 
plant material is carried out to sea and after drifting around for 
some time ultimately sinks to the bottom and thus provides food for 
such bottom organisms as prefer this kind of nourishment. That it 
may be quite a considerable quantity of plant material that thus sinks 
to the bottom I have myself had the opportunity of observing through 
the medium of some trawlings off the southern coast of Mindanao, 
the mud contained in the trawl consisting largely of decaying vege- 
table matter. 
Not all the deep-sea echinothurids are vegetarians. Thus speci- 
mens of Phormosoma bursarium, taken in the same haul with 
Hygrosoma luculentum, had only pure mud in the intestinal canal, 
whereas the Hygrosomas had their intestines filled with plant ma- 
terial. This is the more remarkable since the sharp, pointed teeth of 
Phormosoma would seem poorly adapted for mud eating. 
The imbrication of the plates of the echinothurids, combined with 
their mostly very delicate structure and the great size attained by 
most of these deep-sea echinoids, results in the deplorable fact that 
they are as a rule very poorly preserved—fiattened like a pancake 
and very often torn to pieces—thus giving a very poor idea of what 
these sea-urchins really look like. Having for a long time deplored 
this fact, I conceived the idea that it might, by carefully stuffing 
them, be possible to make them assume, at least to some degree, their 
natural shape. The idea proved a decided success, and I succeeded 
in making even hopelessly torn individuals assume a tolerably good 
shape. Such stuffed specimens will retain their form equally well 
in alcohol or in a dried condition. 
The number of species of echinothurids known from the Malayan 
seas is very considerable—21 out of a total number of about 50. A 
