Abstract
Only 1 micro-scopic crustacean (adult about 3 mm. in length), LEP-IDOCARIS rhyniensis* (p. 155), has been found in these Middle or possibly Lower Devonian beds. Its relationships necessitate the erection of a new order and family of Branchiopoda: LIPOSTRACA, LEPIDO-CARIDIDAE. Owing to the semi-transparent nature of the chert, it has been possible to reconstruct the animal in practically all external details. Both sexes in various stages of development are represented and figured. Some of its details seem to throw important light on the evolution of crustacean appendages. The absence of all certain traces of "pond-life" organisms other than L. rhyniensis seems to confirm the theory that the water in which the Rhynie Chert Bed was deposited may have been hot and highly charged with silica. [See also following entry.].