lpaul

It appears that erythroryncha is the correct spelling, although it is frequently spelt erythrorhyncha.

HBW states as such, but without explanation:

Taxonomy: Corvus erythrorynchus Boddaert, 1783, Canton (Guangzhou) south China.
Genus has sometimes been subsumed in Cissa, but three members of latter seem to form a distinctive group. Present species forms a superspecies with U. caerulea and U. flavirostris. Race alticola initially described under name "caerulea", but this name is invalid, as preoccupied. Species name often misspelt "erythrorhyncha". Five subspecies recognized.

A more helpful discussion can be found at:
http://www.birdforum.net/showthr ... light=erythroryncha
This states that Boddaert when describing the species used erythrorynchus (which for grammatical reasons became erythroryncha when the species was later transferred to Urocissa) and provides a link to a reprint of this reference.

Hope this helps.