Publication of the decades-long Treatise on Invertebrate Paleontology is a work-in-progress; and therefore it is not yet complete: For example, there is no volume yet published regarding the post-Paleozoic era caenogastropods (a molluscan group including the whelk and periwinkle).
Raymond C. Moore, the project's founder and first editor, originally envisioned this Treatise in invertebrate paleontology as comprising just three large volumes, and totaling only three thousand pages.
The project began with work on a few, mostly slim volumes in which a single senior specialist in a distinct field of invertebrate paleozoology would summarize one particular group.
From the beginning, the character of the Treatise volumes has followed and further developed the pattern of the classic Invertebrate Paleontology written by Moore, Lalicker and Fischer (1953).
Following their lead, the Treatise includes in a typical article (a) a description of the basic anatomy of the modern members of each invertebrate group, (b) distinctive features of the fossils, (c) a comprehensive illustrated glossary of terms, (d) a short discussion of the evolutionary history of the group, (e) a stratigraphic range chart, done at the level of the major subdivision (lower, middle and upper) of each Geologic period.
Not only that, but the more recent volumes and revisions also include (l) new fossil and phylogenetic discoveries, (m) advances in numerical and cladistic methods, (n) analysis of the group's genome, (o) its molecular phylogeny, and so on.