262 
THE VOYAGE OF H.M.S. CHALLENGER. 
any peculiar features, nor do they particularly abound. The very remarkable Rhopalodina 
has been hitherto only dredged at a single locality. In different regions different 
forms predominate ; thus the Aspidochirotse abound in species at the West Indies and 
also in other tropical or subtropical zones. The Mediterranean has a Holothurian fauna 
very different from that of the West Indies, but reminding one in several respects of 
that of the British and Scandinavian coasts. 
The Indian and Pacific Oceans. — Considering the fact that while about forty-two 
species and varieties are known from the Arctic Ocean, thirty-two from the Antarctic, one 
hundred and thirty-five from the Atlantic and Mediterranean, but no less than about 
three hundred and five from the Indian and Pacific Oceans, there seems to be sufficient 
reason for the opinion that the Holothurids attain their maximum development in these 
latter seas. Here, as well as in the Atlantic Ocean, the tropical and temperate regions are 
the richest, while a diminution in the abundance of Holothurian life takes place towards 
the arctic and antarctic regions. The fact that among eighty-nine species hitherto known 
from the Indian Ocean, forty-nine are also found in the Pacific, evidently proves the great 
similarity between the two oceans, a similarity which wiU certainly be more striking when 
a greater part of the Indian Ocean is explored. 
The genus Synapta is represented by no less than thirty-four species, of which some 
attain an enormous length ; the large Synapta heselii, Synapta glabra, Synapta grisea, 
&c., are not only by their size, but even by their colour and external appearance, in a high 
d egree characteristic of the oceans in question. The genera Actinocucumis, Pseudocucumis, 
Amphicyclus and Eucyclus are known only from these oceans, and show that those Dendro- 
chirotse which are marked by possessing more than ten tentacles, have been subjected to 
greater variations here than in the Atlantic Ocean. The singular genus Colochirus is very 
characteristic of the Holothurians of these oceans, and gives to them a peculiar stamp, 
for among eighteen known species, seventeen belong to the Indian and Pacific Oceans. 
Among the Aspidochirotse, Miilleria, Stichopus and Holothuria abound in all places, and 
are represented by a very much greater number of forms than is the case in the Atlantic 
Ocean. 
