266 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



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 mono- 

 cyclic, 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 sand- 

 stone slab from the Eocene formations outcropping along the Poto- 

 mac 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 ob- 

 tained 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 par- 

 titions {Columnaria vacua Foerste), and still others with spongy 

 walls {Calapoecia cribriformis Nicholson). Large stems of fluted 

 or nodular hydrozoans {Beatricea) are scattered among the honey- 

 comb 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 





