Mryntu

"Ramakrishna in bhava samadhi at the house of Keshab Chandra Sen. He
is seen supported by his nephew Hriday and surrounded by brahmo
devotees."

Can any scholar here, identify this hand Mudra done by Ramakrishna Paramhans by his right hand and its importance in Yog and Samadhi?

The same Mudra can be seen in Lord Shiva's left middle hand as well.Is it superior to Gyan Mudra for Samadhi?

Apana mudra, also called as the purification mudra, is a hand gesture that detoxifies and purifies the body and balances the elements of space and earth within it. It eliminates waste, toxins and chemicals in the body and prevents deseases and illnesses.Apana mudra is performed by bending the middle finger, the ring finger and the thumb so that the tips of these fingers are touching. The index finger and little finger remain straight. This mudra is usually practiced with both hands.

Apana mudra is sometimes also called cleansing mudra or energy mudra. It generates energy in the liver and gallbladder and supports balance and harmony. It is also improves digestion and is believed that practicing this mudra can help when the childbirth is delayed.

Apana mudra increases the vata and kapha doshas in the body and decreases the pitta, thus helping to balance the three doshas in the human body.It is best to practice this mudra in the mornings. People with vata and kapha constitution should practice this mudra in moderation.

While Gyan mudra, or chin mudra, often used while meditating, is one of the most important mudras that promote physical and mental health. From Sanskrit, chin (or cin) means "consciousness" and mudra means "gesture" or "seal." Therefore, gyan mudra may be translated to mean "gesture of consciousness" in English.

Gyan mudra symbolizes the union of Self with the universe, the unification of one's soul and the supreme Soul. The thumb symbolizes the supreme Soul, the index finger refers to the practitioner's soul, the middle finger represents sattva ("purity" and "true wisdom"), the ring finger represents rajas ("passion" and "action"), and the little finger symbolizes tamas ("lethargy" and "darkness"). Gyan mudra is an excellent representation of the yogic philosophy of evolving from the state of ignorance to wisdom and from darkness to enlightenment. Practicing this mudra helps the practitioner to eliminate negative forces and focus on attaining true knowledge

That is known as the Mriga-Mudra.That is mentioned in the dhyana-Mantra of Lord Shiva:

dhaayet nityam mahesham rajatagirinivam chaaru-chandra-avatamsham/ ratna-aakalpa-ujjvalangam prasu-mriga-vara-abhiti hastam prasannam/padma-aasinam samantaat stutam amarganair bhyaghrakrittim vasanam/vishvadyam visvavijam bhavabhayaharam panchavaktram trinetram --Reference :Stavakusumanjali,Udbodhan.

Normally mind is compared with a running deer and this mudra signifies keeping the mind still in case of Lord Shiva, as He holds parashu (axe) in other hand that signifies slaying the deer ie calming the mind.

But Sri Ramakrishna so far as I know did not use any such mudra intentionally.All was the effect of divine ecstacy.But it looks like Mriga-Mudra. The question of superiority or inferiority does not aruse by the way,Only Lord Shiva, known as the Pasupati (Mriga is a Pashu) has Mriga-Mudra in His hand.
The image enclosed by you is a retouched one.I am enclosing a copy of the original for your perusal.