I don't know whether this specific work is considered to be valid, but here
are the general rules. Rarity and anonymous publication are not obstacles
to the validity of da Costa's publication, but inconsistent use of
binominal nomenclature may be.
 
Anonymous publication was allowed before 1951 (ICZN, Art. 14). It is now
banned.
 
Present rarity of a work is not an obstacle to valid publication, though
the work must have been "issued publicly for the purpose of providing a
permanent scientific record", obtainable (at least in principle), and
produced by printing or some other method that "assures numerous identical
copies" (Art. 8). There are examples of works that were printed in large
numbers, but whose edition was destroyed by fire (bombing) before most of
the copies could be distributed. There is even one case where a
malacologist (Isaac Lea) is said to have bought up and destroyed most of
the edition of a major work by his rival (Timothy Abbott Conrad, a distant
relative of R. Tucker Abbott). This work is very rare in its original
edition (about 15 or 20 copies are known), though the Paleontological
Research Institution has reprinted it twice and the latest edition is still
in print. The species named in these publications are valid despite the
rarity today of the original edition. There is no threshold number of
copies that constitutes "publication", but I would question whether an
edition of only ten copies is enough.
 
For valid publication, an author must consistently apply the principle of
binominal nomenclature in that work. In works published before 1931, the
author is given the benefit of the doubt if he or she uses generic names by
themselves without adding specific names or at least the noncommittal
abbreviation "sp." (Art. 11). Also, if a book index published before 1931
is consistently binominal, then it can be accepted as valid even if the
remainder of the book is not. Of course, subspecies are allowed under
binominal nomenclature, even though this results in three names. After
1930, the rules are stricter.
 
Andrew K. Rindsberg
Geological Survey of Alabama