candledave (#19), I suspect, like me, that you have the same Field Guide to the fauna in question which gives the same genus for six of the eight examples, making your explanation of "...two thematic in name only" correct.
My mistake was to double-check Chambers for those that have an entry. I found one listed with a different genus which is the cause of my confusion. (I always thought that the taxonomic name was to avoid confusion over different local names for a species — not the other way round!)