This is Ardhanarishwar, Siva and Parvati in a combined form. Ardhanarishwar’s literal translation is “Half woman Shiva”. Here Siva’s left half is Parvati, his Sakthi (Energy). Ardhanarishwar represent “the inseparable union of the masculine and feminine elements in the creator”

First the story:

“According to Saivite mythology, Sage Bhringi, whose devotion to Siva is exclusive once found Parvati sitting very close to Siva. The Sage could not ask her to move, yet he wanted to worship to be directed to Siva alone. Quickly he assumed the form of a bee, circumambulated Siva and flew away quickly. Parvati offended by the act wished to attain an even closer union with Siva and performed severe acts of penance to achieve that union. After a period of trial, Siva was much impressed with her devotion and penance acceded to her wish by assuming the Ardhanarishwar form” Quote from R Kannan’s book, referred below.

Ardhanarishwar is standing in Tribanga (triple bend) and on Padmapeetha (lotus pedestal). The Padmapeetha in turn is supported by a Bhadrapeetha. The right upper arm is holding Ankush (Elephant Goad). Shiva’s lower left hand is meant to be resting on his vahana (vehicle), Rishba’s head. Rishab is shown behind the Ardhanarishwar. Parvati’s upper is holding a lotus (possibly) and the lower hand is resting on her hip. Sometime you see Ardhanari with three hands with Parvati shown with one hand.

In this Vigraha, notice the difference between the right side (Shiva) and left side (Parvathi). The differences include, other than Parvati’s breast, rounded face on the left, short lower garment for Shiva Vs a longer one for Parvati and broader hip for Parvati .

The presence of Rishab gives this Vigraha depth that you normally do not come across in Indian Vigrahas.

This Vigraha is about 9.5 cm high and it is from Tamil Nadu. This may be dated to the seventeenth century if not earlier. The wear is quite considerable and the face was possible recut.

An example of Ardhanarishwar from Melakadambur is on the right. It is one of few Ardhanarishwar sculptures with Rishab. Photo courtesy Sivashankar Babu, through Facebook pages.

References: 

H Krishna Sastri 1916 South Indian Images of Gods and Goddesses

Dr R Kannan 2015 Manual on the Bronzes in the Government Museum, Chennai