I note that this birth index entry shows the given name as 'unnamed'. so L Rex is presumed based on Henry Field MARSH's obituary, and an Email note from grandson Peter.
[S34] Births Tasmania, 2 May 2020.
On 27 June 1887, at Hobart, [unnamed] MARSH, male.
Father Henry Field MARSH.
Mother Emma Jane JOHNSON.
Transcribed from a birth index (LINC Tasmania on-line record).