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Mr. P. W. Bassett-Smith on 
on which coral-growth is most luxuriant ; from the edge of this 
there is a more or less abrupt descent to a depth of about 30 
fathoms, followed by a gradual slope to 50 fathoms ; then there 
is an abrupt descent to 100-150 fathoms, and beyond this 
the average slope to deeper water is at an angle of about 30°, 
except in section F, near Itu-Aba, where it is somewhat less. 
In section C the slope of the plateau continues gradual to a 
depth of 30 fathoms, and in this respect is similar to the 
Macclesfield Ban k 
The Macclesfield Bank (PL XIV.) is situated 300 miles to 
the north of the Tizard ; it is 76 miles in length and 36 broad. 
This bank is entirely submerged ; the shallowest portion of the 
rim is 9 fathoms beneath the surface, and inside the bank the 
depth is from 40 to 50 fathoms. Dredging on this bank was 
carried on from a small steam-cutter, but at depths of 20 to 
45 fathoms there was considerable difficulty in moving the 
dredge with swabs attached. Living corals were found very 
abundantly to a depth of 30 fathoms, and some were obtained 
from a depth of 44 fathoms. 
It will be seen from the subjoined tabular list that 129 
species of Madrepore corals (Hydrocorallines and Alcyo- 
narians are not here included) have been determined from the 
Tizard and Macclesfield Banks ; of this number 99 species 
are from the Tizard and 26 from the Macclesfield Bank, 
whilst 4 only are common to both. Of the Madreporaria 
Aporosa there are 48 species, belonging to 23 genera ; of the 
Madreporaria F ungida 23 species, included in 9 genera ; and 
of the Madreporaria Perforata 58 species and 8 genera. 
The preponderance of the species of this latter division is 
principally due to the number of forms of the genus Madre - 
pora , of which there are as many as 31 species. 
An analysis of the bathymetrical distribution of these corals 
shows that at depths of 5 fathoms and under there are 45 
species; between 5 and 10 fathoms 43 species; between 10 
and 20 fathoms only 1 species ; between 20 and 30 fathoms 
30 species ; between 30 and 40 fathoms 13 species ; and 
between 40 and 50 fathoms 6 species. The rarity of species 
at depths between 10 and 20 fathoms may be accounted for 
by the fact that the shore-platform abruptly ceases at the 
upper limit of this zone, and there is a nearly vertical descent 
of 10 or more fathoms to a lower platform. 
A very noticeable fact is the number of species which have 
been found living at depths of over 30 fathoms, a depth until 
lately supposed to be the extreme limit at which reef-building 
corals could exist. On these banks, however, we find 19 
species occurring at depths between 31 and 45 fathoms; but 
