Hemogregarines (Apicomplexa: Adeleiorina) are the most common, widely distributed, and speciose of reptilian hemoparasites and infect each of the orders of living reptiles, including the Rhynchocephalia (the tuatara). Three families of hemogregarines are presently recognized, the Hepatozoidae, Haemogregarinidae, and Karyolysidae, each distinguished by very different developmental patterns in their invertebrate hosts in which sporogony occurs. Perhaps 400 species have been described, mostly under the fallacious basis of “presence in a different host indicates specific identity” (Telford, 1984b). Regrettably, almost all species described before the late 1960s were known from the erythrocytic stages alone or, in the case of a few, from circulating cells and divisional forms in fixed tissues of various organs. Ball (1967) attempted to discourage their description just from the stages in blood cells alone, and this has contributed to a reduction in the number of species descriptions since that time, except when accompanied by data on sporogony in a competent invertebrate host. Indeed, most hemogregarines cannot be reliably placed within one of the four genera that occur in reptiles without this knowledge because the usual stages found in blood cells are the gamonts, many of which are very similar in appearance. When used in combination with a description of sporogonic stages, gamont morphology can be helpful, but its use alone is not acceptable. The species accounts below include only those with enough data to ensure their generic identity.