( AMPHIBIA : ANURA )

—In this report emphasis is placed on the dorsal skull characters of the genus Spea and the three species, bombifrons, hammondii, and intermontana. Spea hammondii is a polytypic species with at least three subspecies, hammondii, multiplicatus, and stagnalis, each of which is described and the distribution indicated. Drawings and photographs ofskulls are provided for each species, with hammondii and intermontana receiving special consideration. Few North American amphibians have had such a varied and uncertain systematic past as that of the spadefoot toad. Recent fossils have aided researchers in understanding the relationships between historic and modern species. These relationships strongly suggest that all spadefoot toads be retained in the family Pelobatidae. Cope (1875), based on material available to him, placed American species in the family Scaphiopodidae including two genera, Scaphiopus Holbrook (1836) and Spea Cope (1875). The purpose of this study is a review of the species and/or subspecies of those taxa referable to the genus Spea; included are S. bombifrons Cope, S. intermontana Cope, and S. hammondii Baird. It is not the intent of this study to become involved in further justification of the family or a review of the generic taxa. This has been repeatedly discussed by numerous authors (Cope 1875, 1889, Tanner 1939, Zwiefel 1956, Tihen 1960, Holman 1963, Kluge 1966, Estes 1970, Brown 1976, Tanner 1989, and others). The fossil record for the genus Spea, as reported by Holman (1963), Tihen (1960), Kluge (1966), Estes (1970), and others, indicates that Spea has been an identifiable group in the Great Plains of central North America since the Lower Miocene (S. neuter, Kluge 1966) and the Early Oligocene (Eopelobates grandis, Zweifel 1956). If we accept the conclusions reached by Kluge (1966) that the dichotomy between Scaphiopus and Spea may have occurred as early as Late Miocene and has apparently continued to differentiate to the present, and since we can recognize each genus morphologically and can also delineate distinct differences in the life history of each, then it seems logical to recognize each generic group as distinct rather than to retain them in an inconsistent taxonomic relationship. I consider the skull of Scaphiopus, with its dermal plates, to be primitive. This character is, I believe, more than a slight difference when compared with the skull of Spea. The loss of the dermal plates in Spea is considered a derived character. Obviously there are similarities that relate Scaphiopus and Spea, similarities that place them both in the North American branch of the family Pelobatidae. Based on the distinct differences in the skulls and other morphological, life history, and ecological differences discussed by Bragg (1944), Blair (1955, 1956), Zweifel (1956), and Kluge (1966), I am persuaded to accept Spea as a genus rather than to continue dealing with a Scaphiopus-Spca complex (Tanner 1989). The skull and external characteristics are well documented for bombifrons and intermontana. There is doubt as to whether hammondii has been adequately examined, particularly with regard to the skull characters and their relationships to the populations occurring in areas in southwestern United States and western and southern Mexico. Tanner (1989) demonstrated that the skull characters of Spea hammondii occur in a large series of populations, including those from southwestern United States and northwestern Mexico. By including those populations having a large frontoparietal fontanelle in one species Life Science Museum, Brigham Young University, Provo, Utah 84602.