Close To Critical by Hal Clement

Publisher: Ballantine, No. U2215, 1964. 190 pgs. Mass Market Paperback in very good condition. The previous owner's name is written on the front free end paper, otherwise, a bright, tight, & clean copy. An original publication not a reprint. "Shrouded in eternal gloom by its own thick atmosphere, Tenebra was a hostile planet..a place of crushing gravity, 370-degree temperatures, a constantly shifting crust and giant drifting raindrops. Uncompromising - yet there was life, intelligent life on Tenebra. For more than twenty years, Earth scientists had studied the natives from an orbiting laboratory..and had even found a way to train and educate a few of them."