In 1941, Dr. William F. Jenks sent rich collections of fossils, made in the course of his field work in the Cerro de Pasco region of central Peru, to Dr. Otto Haas, of the American Museum of Natural History, New York, for identification. Ever since, a steadily increasing amount of Peruvian fossil invertebrates has been accumulating at the Museum. Collections made during 1943–46 by Dr. Norman D. Newell in central, eastern and southern Peru, by Mr. Bernhard Kummel in northern, central and eastern Peru, and by Dr. Jenks in southern Peru have since been added to that initial material, and it is hoped that additional collections will be brought in by a forthcoming expedition to Peru under Dr. Newell's leadership. Besides Palæozoic assemblages, to be studied and published separately, most of those collections are of Mesozoic age. The work of description is being divided among several specialists. So far, Dr. Raymond E. Peck and Mr. Reker have just finished a report on charophytes from various regions and horizons, intended for publication in the American Museum Novitates, Dr. John W. Wells will study the Anthozoa and Porifera, Dr. Newell has taken charge of the pelecypods, and Dr. Kummel will concentrate on Triassic cephalopods. Dr. Haas is studying the Post-Triassic cephalopods and the gastropods. Some important groups, especially the brachiopods, which are second only to the molluscs in number of specimens, are still waiting for specialists to undertake their study. The Institute Geológico del Peru, the director of which is Dr. Jorge Broggi, is co-operating with the American Museum of Natural History in all this work.