The word myriad works as both (1) an adjective meaning innumerable, and (2) a noun referring to an innumerable quantity of something. Using it as an adjective is usually more concise.
For instance, in these sentences the words a and of could be removed from a myriad of with no loss of meaning:
There is unrest in Iraq as well, and a myriad of conflicting interests [and myriad conflicting interests]. [National Review]
The environmental reviews began in the summer of 2007 and included a myriad of public meetings [and included myriad public meetings] and ample avenues for public comment. [Buffalo Business Journal]
Applied to mass nouns
Because a myriad traditionally consists of a number of things, the word is at least a little illogical when applied to mass nouns. In the following sentences, for example, construction settlement and ’90s rap are mass nouns, so using myriad in reference to them is questionable:
Even this freeze has largely been ignored by the government, which has approved a myriad of settlement construction since the announcement. [Antiwar.com]
Since there was no radio in the truck, Tonia regaled us with a myriad of 90s rap while en route to our trailhead. [Huffington Post]