The first attempt at a systematic classification of cavernicolous organisms was made by Schidote (1851). He grouped cavernicoles into Skyyge-Dyr (shade animals), Tusworke-Dyr (twilight animals), Hule-Dyr (cave animals) and Drypsteenhule-Dyr (stalactite animals). In the first class were placed those organisms having a preference for a cool, moist habitat and which were occasionally found at cave entrances. The second class consisted of organisms that periodically penetrated into the dark recesses of the cave. The third class was composed of organisms that lived their whole life in total darkness; the terrestrial forms were blind, while the aquatic forms had organs of sight. Finally, in the fourth class were blind, wingless, nonpigmented forms. Schiner (1854) modified this classification and first proposed the three categories which are the basis for cavernicolous classification today. The first, trogloxenes, includes all organisms which may be found occasionally in caves. They do not complete their life cycles in total darkness. The trogloxenes are predominantly an epigean fauna although some hypogean arthropods are included in this group. In the second category are the troglophiles, organisms that spend part or most of their life cycle in caves. Some of these are adapted for a hypogean existence and thus readily survive in the cave habitat. A majority of troglophiles are facultative cavernicoles while all the members of the third group, the troglobites, are obligative cavernicoles. These are blind or have nonfunctional optic organs, manifest little pigmentation and have developed highly sensitive tactile organs. In 1896, Hamann, utilizing Schiner's categories, classified all the known European cavernicoles and listed 382 troglobitic species, although many were subsequently regrouped as troglophiles or trogloxenes. His list included one vertebrate (Proteus anguinus), 16 gastropods, 229 insects (including 196 Coleoptera), 14 myriapods, 5 chilopods, 83 arachnids, tO cruLstaceans and 24 other species in other orders. Although numerous papers on cavernicoles were published during the next thirty-five years by such eminent investigators as Chappuis, Cope, Jeannel, Martel, Packard, Racovitza and Spandl, it was not until the appearance of the classic Animalium Cavernarum Catalogus (Wolf, 1934-1938) that any attempt was made to present a checklist of cavernicolous organisms of the world. This work includes trogloxenes, troglophiles and troglobites. No previous attempt has been made to publish a checklist of troglobitic organisms of the United States, although checklists of a few families and of several limited geographical areas are available. Dearolf (1937, 1941, 1953, 1956) has compiled lists of the invertebrate and vertebrate fauna found in North American caves, but these do not contain information on ranges nor are they necessarily complete. Individual state lists are too numerous to mention but none of these are limited to troglobites.