The proposed Massachusetts Conservatory of Arts, Science and Historical Relics.
During the filling and development of Boston's Back Bay, there were many grand schemes proposed for how the land would be used. The area that became the Public Garden was the first to be filled, extending land that had once been the shore of the Bay and home to a rope walk (that is, rope factory). There was immediate pressure to sell off the land for housing, but the city kept the land with the intention of putting it to the public good.
The above building, proposed by a Mr William E. Baker, Esq, was based on the Zoological Garden in London and the Jardin des Plantes of Paris. This was before the Natural History Society building was erected (as described in an earlier entry) so there was need for such a facility. However, the building as designed was apparently not appreciated, and the land was left for a garden park.