I happen to have Lambrecht's Handbuch around, and he
mixes up the dates and to make the lapsus "Siemensi".
It seems that the reference for Archaeornis is either
Dames 1884, or Petronievics 1923, or (possibly)
Petronievics & Woodward 1917.
The man to ask is George Olshevsky, who did a great job sorting out the
perplexing array of genus and species names given to the various
_Archaeopteryx_ specimens. I wish George had published it. There may be a
message by him that summarizes _Archaeopteryx_ nomenclature in the DML
Archives. Or else ask him directly - his email address is also in the
archives.