A wentletrap. Colorized from  Webster's New International Dictionary of the English Language,1911, (reference).

For a discussion of some of the places they pop up in nature see http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fibnat.html#spiral .

For some of their appearances in art, architecture and music, see http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fib.html

The ratio of successive Fibonacci numbers converges to a special number, f=, with the k^th Fibonacci, being expressible in closed form as .      

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