El Karstina 1956 Buffo boreas April 21 Mojave River 9:40 p.m. Bull-dozed area adjacent to cotton delta along the river. Calls of B. microcephalus brought me to this area, some 75 yards in width. Tall cottonwoods border the river on both sides. Hylo clamis active. Bob Steblins took a couple of & microcephalus up on dryish sand. Bull-frogs abundant river margin. Small adult ? boreas in puddle 2" deep left by bulldozer. Choral was 14.5°C.; water 16.2°C air 12.8°C. At 9:45 I heard the tremulous notes of an other ? bores. It turned out to be 10 yards from the first. Again the notes are similar to great notes but softer and more melodious. Color a grayish-tan very similar to muddy silt. Other male gravel, smooth-shined. Same to large size (about 85-90 mm.) In several occasions I saw male bores within a foot or two of male or female microcephalus, but the size difference was striking. However, at 10:15 I sounded out a calling grunt of the latter species. No bores notes heard here. In the zone 45 feet from danger (to 1 1/2 feet) main stem I found a ? boreas tightly clasping a large ? microcephalus. Water 2" deep, a shallow slow-moving overflow area for main stem. Sedges scattered, to 14" height. Water temp., 15.7°C at 10:20 p.m. Choral of bores 14.8°C. Air