Cheene, It. 1987 26 November left at approx 0810 w/ Leslie Saul and Norman Gershwim (from San Francisco Zoo), went out the Near Topps to Camino Central 1800, then back across the El Suampo and in on Holdridge Trail for lunch at approx 1215 hrs. Sunny but not too hot. At 0727 hr I had checked the female Bothrops asper on CES, found her back in the 'resting spot' with head facing approx NE (as opposed to SE yesterday at rest). Saw various Norops, Ameira, and a few Eleutherodactylus on the trail - plus of course Dendrobates pumilio. At 0950 hr Norm spotted an adult Mastigodryas melanolomus motionless on the trail, w/ head up, after I had walked over it (1700 Camino Central, 87g, 73 cm + 24.6 cm, female). When seized, she struck repeatedly, spun rapidly about the long axis, and exuded a mild must. I palpated the head and fore-jaw of a Sphenomorphus chersie (swallowed tail-first, approx adult size) from her. At 1020 hr we found a Lachesis muta at CC 1800, as reportedly seen yesterday by Jose Miguel Alvarez. The snake looks to be approx 1.4 m total length, and is coiled under a dry leaf but easily visible, with head facing the trail. It is approx 1.5 m from the base of an adult (fruit pods) Welfia palm. No sign of awareness of us during photographing; might have a food lump. Saw tracks 1 at least