This may possibly be a model in plaster for a statue of Richard I. A work of this title was shown by Charles Augustus Rivers at the exhibition held at Westminster Hall in 1844.
The exhibition was a showcase for frescoes and sculpture by artists who hoped to be commissioned to make works to decorate the new Palace of Westminster (then being rebuilt after the great fire of 1834). We can't be sure that this is Rivers' proposed statue of Richard I because that work was not selected for use at Westminster and the only descriptions of it are generalized. One article praised Rivers' modelling of the face but said 'circumstanced as the figure now is, it could not be executed in marble'. ('Westminster Hall', Art-Union, August 1844, pp. 211-8). The composition of the statuette in this photograph fits this description, to the extent that the undercutting of the sword would have presented technical challenges to the person carving the statue in marble.