Very close to Ditremaster, but differing in having episternal plates strongly offset and uniserial. P. zitteli de Loriol 1881, from the Eocene of India has two gonopores and a perfectly pentagonal peristome like P. mirabile but its episternal plates are biserially arranged. It has been put in a separate genus Skouraster by Lambert, (1937).
The name has previously been attributed to Loven. However, the first use of the name Palaeostoma is that of A. Agassiz (1872) who wrongly attributed it to Loven 1867. In that publication Loven only refers to "tribus Palaeostomata". It is a replacement name for Gray's Leskia, which was a preoccupied name.
Agassiz, A. 1872-1874. Revision of the Echini. Memoirs of the Museum of Comparative Zoology at Harvard College, 3: pts. 1-2: i-xii, 1-378, pls 1-49 (1872); pt. 3: 379-628 +1, pls 50-77 (1873); pt. 4: 629-762, pls 78-94 (1874).
Koehler, R. 1914. An account of the Echinoidea. Echinodermata of the Indian Museum, part 8, Echinoidea (1). Calcutta, Trustees of the Indian Museum.