6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



LEBETODISCUS Bather, 1908 



Theca depressed, circular. Ambulacra curved, five in number, all 

 directed toward the left, with mosaic interambulacral plates. Am- 

 bulacral plate structure apparently as in Carneyella. Anal area well 

 defined in slightly wider interradius. 



Genotype. — Agelacrinitcs dicksoni Billings, 1857. Ordovician 

 (Trenton) of Ontario. Canada. L. loriformis Raymond, 1915, is a 

 second described species. 



FOERSTEDISCUS, n. gen. 



Like Lebetodiscns, but ambulacra all directed to the right, short, 

 broad, and strongly curved, and interambulacral plates polygonal but 

 overlapping toward the center and highly imbricating around the 

 periphery. Anal area of many small, irregularly arranged plates in 

 slightly wider interradial area. 



Genotype. — F. grandis, new species. Ordovician (Trenton) of 

 Kentucky. 



FOERSTEDISCUS GRANDIS, n. sp. 



Plate I, fig. 12 



Theca a flattened disk. 25 mm in diameter, resting upon or attached 

 to a layer of limestone. Ambulacra five, short, broad, all curved to 

 the right, consisting of two rows of elongate covering plates slightly 

 raised along the midline, and a single row of floor plates. Interambu- 

 lacrals large, imbricating, but flat in the central areas, narrow, more 

 numerous, and piled up on edge along the margin. Anal area large, 

 distinct, occupying a slightly wider space, composed of many small 

 imbricating plates arranged in circles, the smallest in the center. 



Although resembling Lebetodiscns dicksoni (Billings), the right- 

 handed arrangement of the ambulacra in this present species is a 

 ready means of separation. 



Occurrence. — Curdsville division of the Trenton, near Troy, Wood- 

 ford Coimty. Kentucky. 



Holotypc. — U.S.N.M. no. S.3191, Springer Coll. 



PYRGOCYSTIS Bather, 1915 



Oral surface of five broad, straight ambulacra mounted on a high 

 cylindrical turret composed of wide, thin, closely imbricated plates. 



Genotype. — P. sardesoni Bather, 191 5. Ordovician (Decorah) of 

 Minnesota. Scalpellum sidcatnm, procerum, and cylindriciim Aurivil- 



