R. Zweifel Isla San Carlos, Sonora, Mexico 1951 83 April 28 Prigym in one of the fissures, but saw no reptiles. However, he didn't get atop the island where the plants were. Isla Chapetone is a low, rounded island with a sandy beach on the landward end. Callosaurus was very abundant here (see species account). Isla Medio seemed to have no slope, though we did not spend too long on it. It was quite rocky and almost entirely covered with quino. Isla Blama has a precipitous, cliff-like periphery, but a rather rounded interior. The surface of the island is littered with flat rocks which concealed numerous insects, spiders (including black widows), centipedes and scorpions, but seemingly no reptiles. Blood found a colony of fish-bats on the island. Both at camp again, a very large Bufo alvarius was seen in the larger pothole, but in a position where it could not be seen. April 29 This morning I shot a couple of Cnemidophorus tigris near the mouth of our canyon, but in its typical tigris habitat, and a blurti a few hundred feet away at our campsite. I also collected seven callosaurus on the beach opposite Isla Chapetone for comparison with those taken yesterday on the island. I drove to Guaymas and then two or three miles further on the road to Empalme to where a power line with attendant road crosses the highway. One mile north on this road I got a C. lortsi and a couple of Mesanza. No Uta could be found, though I looked especially for them. The Mesanza were on rocks. Also saw a Sanomalus on a rocky outcrop, but didn't get it. Went back to Boschiborfor and with Bloodal stuck away.