356 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, wliere 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 Bank. 



The Macclesfield Bank (PL XIV.) is situated 300 miles to 

 tlie 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- 

 rarians 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 Fungida 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 batiiymetricai 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 j 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 j but 



