I am a direct descendant of Susannah Nairn(e)and her son John Riley (born circa 1791-92).  My father was Donald William Riley (1924-1963) and grandfather was Amos Bede Riley. John Riley married convict Catherine Lattimore (from Warwickshire)in 1814. John's mother Susannah Nairn alias Talbot aka Mrs Edward Riley was convicted at the Old Bailey,  London, 1791 for stealing.   She departed Deptford England aboard the 'Kitty' (See “Susannah  Nairn – Convict Beginnings”  for her history.
 Susannah was a widow (of Talbot) when she married Edward Riley in London in 1784. John Nairn  was one of her witnesses. London, See England, Marriages and Banns, 1754-1921 on   http://www.ancestry.com

I'm sure most descendants of John RILEY and Catherine Lattimore are aware that Edward Riley may  not have been John's father. The is no record of any births aboard the Kitty, no surgeon's logs  and no ship's log. If you do the sums: Susannah imprisoned October 1971, in Rio de Janeiro  June/July 1972, arrived Sydney November 1792 (That's 11-12 months).

ORIGINS of SURNAMES: 
 Riley, Ryley: John de Ryeley 1284 Wak; Henry de Ryley 1327 SRDb; John Ryley 1488 CorNt.

RILEY:   Irish: variant spelling of Reilly. 

RYLEY:   English: ‘habitational’ name from Ryley in Lancashire, so named from Old  English ryge ‘rye’ + Leah ‘wood’, ‘clearing’. There is a Riley with the same meaning in Devon,  but it does not seem to have contributed to the surname, which is more common in northern  England.

REILLY:  Irish: reduced form of O’Reilly, an Anglicized form of Gaelic Ó  Raghailligh ‘descendant of Raghailleach’, Old Irish Roghallach, of unexplained origin.   Dictionary of American Family Names, Oxford University Press, ISBN 0-19- 508137-4

The surname 'Reilly' is a patronymic surname meaning "descendant of  Raghallach," a personal name from the Old Norse and introduced by the Vikings.  Ragheallach can be broken down into "ragh" meaning 'race' and "ceallach"  meaning 'gregarious.'   So I see these two names as not variants of a name but completely  different names.

My first RILEY in Australia was spelt RYLEY.  I do not know which spelling is correct for my  ancestors.  However, I do know the words LEE/LEA mean meadow or clearing and as  RYE grows in meadows it seems reasonable to me that this is how their surname originated. "he  who dwells by the rye clearing".
 So far I have not traced them any further than London – maybe they were  from Lancashire, so that’s a new lead for me(I'll take any clue I can get) .