Dirosaurus dorsalis June 3 6 mi N San Jose del Cabo, 250 ft., Baja Calif. Have seen several on the flat sandy terrain here, among ramajo ceniza and yerba de la pasma. They seem to have a characteristic alert position with head and shoulders propped up high on the front legs, while the hind quarters rest flat on the ground. When startled they run quite rapidly for a few feet and stop, at which point will remain indefinitely motionless or nearly so - how long I never had time to find out. With several I very slowly and carefully approached until feet or hands were within one foot of them before they became alarmed. Saw one chasing another, presumably a pair. The first would alternately run a little and walk a few steps, while the other followed at a respectable distance of a foot or two, frequently bobbing erratically. This motion at times appeared to be on one forefoot at a time.