- Smith is lying there watched patiently by Jones.
Am I right that this is two clauses, and that the second is a dependent clause in the passive voice?
Should there be a comma between them, and if so why?
I believe it is a shortening of Smith is lying there being watched patiently by Jones, which makes use of a present passive participle. The participle functions as an adjective modifying Smith.
But as Scott mentioned, it could also be a compound predicate — that is, it is a shortened combination of Smith is lying there and Smith is being watched patiently by Jones.