Interesting conundrum ... we currently have both Kybos smaragdula and smaragdulus listed as names created by Fallen in 1806, and with smaragdulus as the preferred name, which I think is dubious but it is the current stance in PESI, which we normally go with.

I have tracked down all the authors of the synonyms (via GBIF) and after reflection I feel that the correct course of action will be to raise smaragdula to the recommended name, and drop smaragdulus to a synonym, giving the following:

Kybos smaragdula (Fallén, 1806)

Eupteryx viridipes Curtis, 1837
Kybos smaragdulus Fieber, 1866
Cicada smaragdula Fallén, 1806
Cicadula smaragdula Zetterstedt, 1840
Cybus smaragdulus Douglas, 1875
Empoasca ameragdula Bird, 1930
Empoasca mucronata Dworakowska, 1976
Empoasca smaragdula Horváth, 1897
Eupteryx smargadula Bold, 1867
Jassus longeciliatus Graaf, Six & Snellen van Vollenhoven, 1862
Typhlocyba smaragdula Herrich-Schaffer, 1834

Given this, and in the absence of Fallen's type description, I feel that it is likely that Fallen described it as "Cicada smaragdula Fallén, 1806" and in fact it was Fieber that described it as smaragdulus in 1866. Fallen's name therefore stands and authorship is bracketed, signifying the move to Kybos in 1866. 

We currently have:
Kybos smaragdulus (Fallen)            NBNSYS0000010629  (ill-formed recommended)
Kybos smaragdulus (Fallén, 1806)   NHMSYS0020705682  (well-formed recommended - the current preferred name in the nameserver)
Kybos smaragdula (Fallen, 1806)         NBNSYS0100003645  (well-formed synonym - but in fact ill-formed because it lacks the acute diacritical)

So it looks like Kybos smaragdula (Fallen, 1806) needs to be correcting to "Fallén", if possible, and raising to the preferred name ... then the rest making synonyms. Phew, that's a nasty one! ;)