I'm also uncertain about a petition to the Commission. I don't think Coloradisaurus is widely used enough that they will consider conserving it. I think there will have to be a paper either proposing a new replacement name or formally naming Coloradisaurus.Â
> The only hint that it is a replacement name for *Coloradia* is a brief note in the index (pg. 251) which reads "*Coloradia*Â= *Coloradisaurus*". As far as I can tell this would fail Art. 13.1.3 and render *Coloradisaurus* a nomen nudum.
It clearly fails Art. 13.1.3 ("must [...] be proposed expressly as a new replacement name"), because "A = B" is also how ordinary junior synonyms are indicated in the index. (...I grew up with the German translation of 1988 and have repeatedly read the whole book, index included.) Failing Art. 13 makes it a nomen nudum, which is one kind of unavailable name: it does not exist according to the letter of the Code.
I dimly remember a rumor that Bonaparte himself intended to publish *Coloradisaurus*, and that Lambert thought Bonaparte had already published it. No idea why Bonaparte (who recently died) didn't publish anyway, though.
Does Lambert's book count as published? To count as published, Art. 8.1.1 says, a work "must be issued for the purpose of providing a public and permanent scientific record"; public and permanent, yes, but scientific?
I think the best option would be to petition the Commission to set current universal usage in stone and put *Coloradisaurus* Lambert, 1983, on the Official List of Generic Names in Zoology. But I'm not sure about this, I'm not going to do it myself (the manuscript the unregistered names in Scientific Reports, Geology of the Intermountain West and, as it turns out, Royal Society Open Science is still growing), and I'm not at all sure the Commission would agree with such a petition (which would entail, as far as I understand, putting the book on the Official List of Works Approved as Available for Zoological Nomenclature).