Observations on the Habits of the Horned Lizard Phrynosoma m'callii

DURING June and July of 1948 the little known horned lizard, Phrynosoma m'callii (Hallowell) was observed in the dune area between Palm Springs and Thousand Palms Junction, Riverside County, California. In this region the Coachella Valley narrows to a width of approximately 7 miles. Ten miles to the northwest the valley becomes confluent with San Gorgonio Pass, which rises from the desert floor and leads out onto the California coastal plain. The valley floor in the study area bears hummocks of white, fairly fine, aeolian sand, topped by creosote bushes (Larrea divaricata). While creosote bush is the dominant perennial, burro weed (Franseria dumosa) and Dalea Emoryi are also abundant. A composite, Dicoria canescens, is also common but is generally small and does not form the nucleus for large accumulations. The area is one of extreme aridity. The mean annual rainfall recorded over a sixteen-year period at Palm Springs is 5.6 inches (Sprague, 1941). The study area is at an elevation of from zero to 45 feet above sea level. Air temperatures are very high in the summertime, often reaching 46 ? C. ( 115 ? F.) in the shade. A series of temperature readings taken on a typical hummock for a full day showed that all the surface sand, including that in the shade of creosote bushes, was in excess of 55? C. (130.5? F.) by 1:00 P.M. These readings were taken on July 14, 1948. The morphology of Phrynosoma m'callii and some of the following observations indicate that it is primarily an arenicolous form. None of the specimens observed were collected outside areas of shifting sand. To the east of Thousand Palms this lizard was taken in an area of hummocks interspersed with stretches of gravel. This is probably a marginal situation. The covered tympanum and the dorso-ventrally flattened tail and body seem to be adaptations for sand swimming. Stebbins (1944) has correlated the swimming habit with body form for Uma. On two occasions these lizards were sighted along the long lee slopes of hummocks. Both times the animal turned and ran down the slope away from the observer and swam into the sand. They were located by tracking. The lizards apparently dove into the while in full flight as they were found buried about 4 inches beyond the point of entry into the sand. This short swim parallels that of the majority of swims shown by Uma. Whereas the shovel-shaped snout of Uma may be adapted to sustained swimming, the blunt snout of P. m'callii seems poorly adapted to continuance of swimming once initial momentum is lost. The conclusion that true swimming probably does not take place to any extent in P. m'callii after the loss of momentum seems