NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER 13 



at once by the large size of its three oral plates and the very short. 

 broad, rapidly tapering ambulacra with only four or five covering 

 plates in a row. Other features are the well-developed anal pyramid 

 occupying a considerable portion of the interambulacral area, and the 

 row of very large plates immediately encircling the tips of the ambu- 

 lacra. The other rows of encircling plates and the interambulacral 

 plates are small in contrast. 



Occurrence. — Black River (Platteville limestone), Rockton, Illinois. 



Holotype. — U.S.N.M. no. 42105. 



HEMICYSTITES GERMANUS, n. sp. 



Plate 4, fig. 7 



Although apparently closely related to H. curtus in its short, broad 

 ambulacra, the two individuals attached to a brachiopod shell on which 

 the present species is based differ in that the covering plates are 

 smaller and more numerous in each ambulacral row, and the en- 

 circling rows of marginal plates are less differentiated, smaller, and 

 more imbricating. 



Occurrence. — Trenton (Catheys formation), Love Branch, Maury 

 County, Tennessee. 



Cotypes. — U.S.N.M. no. 42140. 



HEMICYSTITES PAULIANUS, n. sp. 



Plate 4, fig. 9 



In general aspect this species is very similar to H. germanus, from 

 which it differs, however, in that the ambulacra are longer, taper 

 more slowly, and contain more covering plates in each row. 



Occurrence. — Black River (Decorah shale, Phylloporina bed), 

 St. Paul, Minnesota. 



Holotype. — U.S.N.M. no. 421 14. 



HEMICYSTITES RICHMONDENSIS, n. sp. 



Plate 5, figs. 5-7 



Theca small, averaging 7 mm in diameter, with ambulacra short, 

 straight, wide, not narrowing much toward their extremity, bearing 

 6 to 8 plates in each row, and surrounded by a broad rim of punctate, 

 wide plates, and then by several marginal rows of smaller plates. 



This rather widespread Richmond species differs from the asso- 

 ciated Isorophus austiiii in that the arms are broad and straight instead 



