Four distinct types of cytological variation are present in the species of Circotettix which have been examined. 1. Asymmetrical bivalents consisting of a metacentric and an acrocentric homologue are present in all four species. C. rabula and some of the material of C. undulatus have three variable bivalents. C. coconino and C. crotalum vary in only the smallest bivalent. 2. Supernumerary chromosomes are present in C. undulatus and C. rabula. Three is the maximum number seen in C. undulatus and two in C. rabula. In individuals with two supernumerary chromosomes, the supernumeraries form bivalents in some cells and remain independent in others. In the individual with three, supernumerary trivalents, bivalents and univalents are present. 3. Based on the cytology in the males, 21- and 23-chromosome types are present in C. undulatus, and a 22-chromosome hybrid is formed when the two types cross. This condition occurs on the edge of the distribution area. 4. Polyploid cells occur in a number of individuals of ...