pieces, for the most part, are fitted together in their natural positions. Associated with these colonies of Uintacrinus are beds of a small oyster, as shown along the margin of this slab. Every characteristic structure of this crinoid is here illustrated by one or more individuals. About 350 calices are exposed upon the surface; 90 are in position to show the base, of which 53 are monocyclic, and 37 dicyclic. Several have the arms visible to great lengths, preserving the details of the delicate pinnules as perfectly as if freshly dredged from the sea. One shows the disk, or tegmen, with its black carbonaceous membrane, from which the food grooves pass to the outstretched arms. From other specimens, it is known that the arms of this species have a spread of 8 feet, being the largest known crinoid, fossil or recent. A portion of this specimen is the original of Plate VIII, of Mr. Springer's memoir on Uintacrinus (Memoirs Museum Comparative Zoology, Harvard, vol. 35, pt. 1). The second is a large limestone slab of much greater geological antiquity, namely, Early Silurian, which consists almost entirely of primitive brachiopod shells and bryozoa. Again, there is a sandstone slab from the Eocene formations outcropping along the Potomac River below Washington which, geologically speaking, is of comparatively recent age, a fact which is indicated by the very modern looking shells occurring in it in great abundance. Finally an exhibit of fossiliferous stratified rocks, limestone and interbedded shales, with two distinct coral reefs preserved. The mass was obtained from the rocks of the Richmond formation (uppermost part of "Cincinnatian group ") near Louisville, Ky. Its purpose is to show the importance of the ancient life of the globe in the formation of rock strata. The lowest layer of limestone is composed largely of fossil brachiopod shells. Next above is a layer with scattered corals belonging to a long-tubed species (Columnaria calicina Nicholson), probably torn by waves from a near-by coral reef. Overlying this is a limestone stratum largely made up of the twiglike stems of stony bryozoans (Trepostomata). The main reef of corals is chiefly composed of the rounded heads of three species of honeycomb corals, some with radial partitions in the tubes (Columnaria alveolata Goldfuss), others without such partitions (Columnaria vacua Foerste), and still others with spongy walls (Calapoecia cribriformis Nicholson). Large stems of fluted or nodular hydrozoans (Beatricea) are scattered among the honeycomb coral masses. Horn corals (Streptelasma rusticum Billings) are to be seen in both the lower and upper coral beds. The spaces between the limestone layers and also between the heads of coral are filled with clay which contains many other examples of fossil |