The genus Mexistrophia (Thompson, 2011) was proposed within Cerionidae to include several species inhabiting cool coniferous forests in the highlands of central Mexico. Mexistrophia is the sister group of all remaining living Cerionidae, which have transitioned from continental to island habitats, where they occur in dense but patchy populations, often containing many thousands of individuals.

Individual populations tend to be fairly uniform in the size and morphology of their shells. Clench (1938:524) noted that the greater the isolation of the population, the greater is the uniformity among its members. Variation in shell morphology among populations can be enormous, not only throughout the geographic range of Cerion, but even among neighboring populations separated by less than 100 meters. This lavish yet geographically circumscribed diversity has led to an extensive body of literature dealing with Cerionidae. Much of the early work was primarily descriptive and focused on parsing the various phenotypes among roughly 600 nominal species and nearly two dozen genera or subgenera. More recent research, particularly the work of Mayr, Gould, Woodruff, Goodfriend, Harasewych, as well as their students and collaborators addressed more basic biological questions, among them the origins as well as the geographic and temporal stability of morphological and genetic diversity, and the dynamics of hybrid zones and biogeographic patterns, both Holocene and Recent.

The greatest diversity of Cerion occurs in Cuba and in the islands of the Bahamas. However, it should be remembered that most the present range of the genus, including southern Florida and many of the Bahamian Islands were submerged as recently as the Eemian interglacial era (125,000 years before present), and have been recolonized since that time.

Many researchers have conjectured that perhaps only 10-20% of the species named within Cerionidae will eventually be found to represent valid species, the rest may be subspecies, demes or merely distinctive combinations of alleles. Although Gould and Paull (1978) reduced the seven described species from Hispanola to the Virgin Islands to a single species using multivariate analyses of shell characters, they reported that 95% of the specimens could be sorted to their source populations using this data.

Cerion are remarkably well suited to studies on many aspects of evolution, population genetics, parapatric and allopatric differentiation.

The purpose of this website is to facilitate such studies by providing taxonomic, biogeographic and bibliographic information about the family Cerionidae. Included is a searchable database of all taxa proposed within the family Cerionidae. Entries for species level taxa provide an abbreviated synonymy that is linked to the bibliography, the text [and if needed an English translation] of the original description, five views of the primary type specimen, as well as information on the type locality and distribution. Also included are links that will enable the user to search the holdings of major museums, and GenBank.