Hi. I have been reading alot about yoga meditation  and buddhist meditation.  You may k ow that dhyna And samadhi  are the 2 mystical or transcendental  states  in raja yoga. Dhyna being a close approximation. To samadhi .  My question ... what would be the the equivalent  to samadhi on the buddhist path of right concentration.  My assumption would be 4th jhana .  Dyhana= 1-3 jhana
 Dharana = access concentration.   Any thoughts

I agree somewhat. I see Samadhi in the Patanjali Yoga Sutra (PYS) as equal to the equanimity nana in Theravada/vipassana, which we could also call 4th vipassana jhana.The Yoga sutras path is often, mistakenly IMO, seen as pure samatha. But it's full of vipassana aspects in there as well.

In PYS Samadhi, for example, Patanjali says that "it reflects equally whatever lies before it - whether subject, object, or act of perceiving." (PYS 1.41). All are seen as mere mind stuff, mind movements, called citta-vrtti in PYS.

He also speaks of the highest Samadhi called Dharma-Mega-Samadhi (rain cloud samadhi), in which one sees quick successions of phenomena arise and pass very quickly, another obvious vipassana aspect.

If you haven't read it yet, I would suggest you read Chip Hartranft's 'The Yoga-Sutra of Patanjali; A New Translation with Commentary`

I think it's difficult to give one answer to this question because interpretations vary a lot more in hinduism, than they do in buddhism. It's a good discussion nevertheless

Godfrey Devereux's book Yoga Unveiled, commentary on Patanjali's sutras, might be of interest. Here is his Guru Viking interview.