Two species groups of schizomids occur in California and Arizona. Their low vagility and inability to disperse through suboptimal areas make their present distribution largely a product of the geologic and climatic events since the Miocene. The relictual nature of most schizomid populations testifies to the vicis- situdes of the northerly latitudes during the Pleistocene and Recent epochs for these Neotropical-Tertiary and Madro-Tertiary representatives. The arachnid order Schizomida contains about 75 species, mainly tropical; however a few taxa are present in temperate areas in Cali- fornia and Arizona. Little is known of the feeding habits of schizomids, but they prob- ably prey upon small invertebrates throughout life. Six instars occur in a period of 2-3 years. Schizomid habitats are characteristically moist and dark. These arachnids are extremely sensitive to dessica- tion and therefore inhabit leaf litter and cavities beneath rocks and logs where adequate moisture is present. Moist habitats become scarce in California in late spring and schizomids decrease in abundance at this time, likely retreating into the soil until autumn rains arrive. This habit enables temperate schizomids to survive in a macroclimate quite different from that of the humid tropics. The low vagility and inability of schizomids to disperse through suboptimal areas may account for their geographic distribution. They lack any secondary means of travel, such as phoresy, ballooning, resistant eggs, parasitism or other means employed by archnids. A few species, such as Trithyreus joshuensis Rowland (1971), and T. borregoensis Briggs and Hom (1966), are found in very restricted habitats. Both species are limited to small desert palm oases. Other California taxa such as an undescribed subspecies of T. pentapeltis (Cook, 1899) and T. belkini McDonald and Hogue (1957) range more widely. These occur in many locations in mountain foothills and canyons at low elevations. The highest elevation recorded for schizo- mids in California is for T. joshuensis at about 2400 ft. Snow occasion- ally falls here and summer temperatures are very high. This climate