2 literature references for Spongia rigida Montagu, 1818:

Author: Van Soest, R.W.M.
Year: 2001
Title: Porifera, in: Costello, M.J. et al. (Ed.) (2001).
Source: European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50:
Author: Montagu, G.
Year: 1818
Title: An Essay on Sponges, with Descriptions of all the Species that have been discovered on the Coast of Great Britain.
Source: Memoirs of the Wernerian Natural History Society 2(1): 67-122,pls III-XVI.