# What's the proper name for these chain structured PGMs?

I'm trying to find previous work that has dealt with this type of PGMs, but don't know what to call them:

a) "recurrent HMM"? $$y_i$$ are scalars and $$x_i$$ are discrete

b) "triangle HMM"? again, $$y_i$$ are scalars and $$x_i$$ are discrete