A PLETHORA OF MYRIADS: My old buddy Bill Sherman says:

"...[T]he American Heritage Dictionary uses "myriad" as both adjective and noun (usage two: noun, A vast number. From the Greek murios to mean countless). So it's grammatically correct, even if it does sound clunky...

*Ulp*. And to think I've been correcting my betters for all these myriads of years. Hopefully, I'll keep an open mind about the organic nature of language from now on. From Dictionary.com, here's more:

Throughout most of its history ... myriad was used as a noun, as in a myriad of men. In the 19th century it began to be used in poetry as an adjective, as in myriad men. Both usages in English are acceptable, as in Samuel Taylor Coleridge's “Myriad myriads of lives.” This poetic, adjectival use became so well entrenched generally that many people came to consider it as the only correct use. ...

Live and learn.