In answer to yours of the 17th, we have no separate copy of Dr Casey's paper on Cyclides and Sphero-quarties. I am afraid it can only be obtained by purchasing the volume of "Philosophical Transactions" ['Philosophical Transactions of the Royal Society'] in which it appears, namely 1871 Part II, price £2-5-0.
Asst. Sec. R.S. [Assistant Secretary, Royal Society]'.