XXXVIII. H. D. WALSH. 
tion on marine borers I might refer to a valuable paper by 
Mr. C. Hedley, F.L.s.*. I exhibit several specimens of the 
various borers; I have been unable to procure any large 
specimen of the Teredo, but may mention that in the 
brackish waters of the Mvyall Lakes and on some of the 
northern rivers I have seen Teredo quite 6 feet long and 
nearly three-quarters of an inch in diameter. The hard 
shell head which is said to act as a clutch to keep him up — 
to his work is an interesting tool. It will be seen that the 
Sphaeroma greatly resembles the common or garden wood- 
louse, and [am informed that it belongs to the same family. 
Yellow Metal.—The general experience of engineers 
during the last six or eight years has been that yellow 
metal sheathing is not as durable as it used to be. The 
sample taken from a pile of the old Pyrmont Bridge which 
has been immersed in sea-water for 48 years, though worn 
through in places is otherwise sound metal, fairly flexible, 
and polishes brightly. I have seen other samples propor- 
tionately good taken from piles in some of our coastal 
harbours which have been standing in the salt water for 
upwards of 25 years. On the other hand the sheathing of 
both vessels and piles with yellow metal has during the last 
few years been attended in many instances with conspicuous 
failure. Information of similar experiences has also come 
to me from Queensland and other States, and I am informed 
that complaints have latterly been so wide-spread that 
they have reached the manufacturers in England from all 
parts of the world. The manufacturers have stated that 
they are unable to afford any explanation of this sudden 
and rapid deterioration. Chemical analysis shows that the 
zinc in the alloy almost entirely disappears, leaving a brittle 
cellular copper skeleton. It has been suggested that the 
modern electrolytic process in the production of copper 
1 Journ. Austr. Assoc. Adv. Science, Vol. viit. 
