112 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
rated, which lead towards the 100 fathom line, and form a uniformly 
sloping channel from the inner reef channel to the sea. There being no 
outer Barrier Reef patches, or outer reef channel, as along other parts of 
the reef (as south of Lark Pass, for instance, and elsewhere), where 
the outer Barrier Reef forms a series of linear or curved reefs, separated 
from the inner reef patches by a channel of from twelve to twenty fath- 
oms in depth. With the exception of the few insignificant reef patches 
scattered across the middle of Trinity Opening, that channel is flanked 
on the north by Butt Reef and on the south by Oyster Reef, both of 
which are reef patches forming the eastern flank of the inner Barrier 
Reef channel (Plate XXXI.). 
Before going on with the description of the inner and outer reef 
patches, it may be well to give that of the smaller island groups north 
of Trinity Opening as far as the Lizards, many of which are gradually 
changing into reef flats. 
Continuing our examination of the islands situated between the inner 
western edge of the Barrier Reef and the mainland, we come north of 
Trinity Opening, first upon the Low Isles situated in midchannel. Close 
to the mainland is Snapper Island. About thirty-five miles north of the 
Low Isles we come upon the Hope Islands (Plate XXXII.). 
The smaller of the Hope Islands to the east is a sandy island flanked 
on the southeast by an immense flat covered by dead coral (Plate VI.), 
and numerous fragments of beach rock, forming an irregular pavement. 
The fauna living under these stones is quite rich, and between them 
were found numerous huge Actiniæ, Aleyonarians, Zoanthus, and Annel- 
lids, as well as an occasional living coral. On the coral reef flat there 
were found many Tridacnas, Holothurians, long-armed Ophiurans, huge 
Synaptas, and splendidly colored Macrurans and Brachiurans. 
On the slope to the leeward of the flat were growing fine patches of 
corals, with sponges, Actinians, Aleyonarians, Fungide, Millepores, huge 
masses of Pocillopora, Madrepores, heads of Astreans, of Gymnastre- 
ans, and of Meandrinas. These heads and patches begin to make their 
appearance in from six to seven fathoms, increasing gradually in num- 
ber and species to between five and three fathoms of water, where they 
land rivers, like the Burnett, Fitzroy, and others. If there has been a subsidence 
of about 100 feet, as indicated by the river beds near Townsville, it is very proba- 
ble that the course of the Queensland rivers extended farther out to the edge of 
the Great: Barrier Reef, and that some of the breaks and passages extending west- 
ward may have been originally due to the action of the rivers, an influence at this 
day reaching only a comparatively short distance from the shores of the mainland. 
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