40 AUSTRALASIAN ANTARCTIC EXPEDITION. 
Atlantic distributed themselves not only around the Atlantic coasts but also eastwards 
into the Indian Ocean, but the principal drift was westward by way of the Antillean 
region into the Pacific, and thence in the main down the west coast of South America 
into the Antarctic realm, whose waters were then much warmer than they are now. 
Hemithyris is regarded as originating in the Boreal region, where the family 
Rhynconellidae is best developed since the Silurian. The four species of the Austral 
region seem to have spread from Japan south through Oceanica, and thence by way of 
New Zealand into Antarctica. This conclusion seems based mainly on the occurrence 
of the species Rhynconella grayi Woodward in the Fiji Islands, but it cannot be regarded 
as yet established that this species is correctly assigned to Hemithyris. 
There are six genera restricted to the Austral region, viz., Agulhasia, Kraussina, 
Bouchardia, Magellania, Terebratella and Megerlina. This region is faunally connected 
directly with Oceanica. The other genera in these waters are regarded as immigrants 
from Gondwana. Schuchert has not discussed the different districts of the Austral 
region or the former land connections which have been suggested between them. 
As regards the deep-sea realm, Schuchert concludes from a consideration of the 
deeper-seated forms whose geological history is known that the present deep-sea forms 
as a rule did not begin to migrate to this habitat earlier than the middle Mesozoic, and 
further, that this adaption is still going on. The truly abyssal forms, as Basvliola, 
Chlidonophora, Frieleia and Pelagodiscus, are probably of stocks even older than the 
middle Mesozoic, and these genera may have begun their abyssal march as early as the 
beginning of the Mesozoic, the period at which the oceans began to get exceedingly 
deep. 
In the subsequent discussion it will be convenient first to consider the abyssal 
fauna, and then to state in detail the distribution of the coastal forms according to 
geographical districts, before discussing fully the significance of the similarities and 
differences that these various districts exhibit. 
THE ABYSSAL FAUNA. 
A distinction must be drawn, as Schuchert has pointed out, between deep-water 
forms which frequent the margins of the continents, and typical abyssal forms which 
occur in the middle parts of the great oceans as well. Of the latter there are only five 
species known, two of which Chlidonophora incerta (Dav.) and Chlidonophora chune 
Blochmann do not occur in the southern hemisphere. Neorhynchia strebeli (Dall) has 
been reported only from the “* Albatross ” station, 4721, in mid-Pacific, in 2,084 fathoms, 
elobigerina ooze, and from Station 4709 southwest of the Galapagos group, in 2,035 
fathoms, ooze. The other two species, Pelagodiscus atlanticus (King) and Terebratula 
Wyviller Dav., have a wide distribution in both hemispheres, The former occurs in 
