The primary content of the Acritax site consists of scans of cards from the John Williams Index of Palaeopalynology. An article describing the index was published by Riding et al. (2012) the abstract from this article makes an excellent introduction to this extraordinary piece of work and is copied below.
The full JWIP catalog is housed in the Palynology Collection of the Natural History Museum in London in the Earth Sciences Department (Economic and Environmental Earth Sciences Division). For access the relevant curators are Dr. Giles Miller and Dr. Steve Stukins. The only part which is currently (2018) available online is the Acritarchs, on this site.
The John Williams Index of Palaeopalynology (JWIP) is the result of the lifetime's work of Dr John E. Williams. Housed at the Department of Palaeontology of The Natural History Museum (NHM) in London, the JWIP is publically available and provides probably the most comprehensive fully cross-referenced catalogue on palaeopalynology in the world. It has 23,350 references to fossil palynomorph genera or species as of February 2012. Since its inception in 1971, every publication in the collection referring to a fossil palynomorph genus or species has been critiqued by John E. Williams.
Each item is given an accession number and appropriately referenced within the JWIP using index cards which are sorted alphabetically. Once added to the main reference subindex, further entries are completed for four themed subindexes. The first three of these are sets of cards on the three major palynomorph groups (acritarchs/dinoflagellate cysts, chitinozoa and pollen/spores), 26 stratigraphical intervals and 17 geographical areas. The fourth themed subindex is where each palynomorph taxon has a card (or cards) listing all the records of that species in the literature within six categories (acritarchs [this is the set of cards used on Acritax], dinoflagellate cysts, chitinozoa, fungal spores, pollen/spores and miscellaneous). Due to the sustained and meticulous recording of data since 1971, users can therefore search the database by major palynomorph group, species, age and/or geographical region. The comprehensive and cross-referenced nature of the JWIP means that researchers can readily identify key publications on, for example, specific palynomorph types over a particular interval in a prescribed area. The JWIP is currently entirely analogue, but the NHM is currently evaluating potential strategies for digitisation.
Riding, J.B.; Pound, M.J.; Hill, T.C.B.; Stukins, S. & Feist-Burkhardt, S., (2012). The John Williams Index of Palaeopalynology. Palynology, 36(2): 224-233.