The description here of Leptodesma falcata new species, continues our ongoing study of bivalve mollusks of the Permian-Triassic faunal crisis. Our collection of silicified valves is from a single locality in the intensively sampled Permian strata of West Texas, which suggests that L. falcata appeared and became extinct rapidly. Such easily missed endemic populations may explain the disjunct records of some Permo-Triassic Lazarus taxa. Unusual features of the new species include its simple dentition, in contrast to the complex array of teeth of middle Paleozoic pterineids, and its evidence of fibrous prismatic microstructure, an addition to the known microstructural variability of the family.