The nomenclature is a little tricky for the London specimen, but for the Berlin specimen, it's a tad clearer. Dames (1897) named the species *siemensi* as a species of *A.*, followed by Petronievics (in Petronievics and Woodward, 1917, in a footnote) who coined *Archaeornis* and designated *siemensi* the type species. So indeed, when specifying only the species name, Dames is the correct citation, and true also when citing the species name in combination with the genus.
A quick note in addition--when assigned to _Archaeornis_, the species citation should have parentheses (since it's not the original combination):
* _Archaeopteryx siemensi_ Dames, 1897 * _Archaeornis siemensi_ (Dames, 1897)
-- Mike Keesey