lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



arrangement of the interambulacrals, the essential generic characters. 

 Cooperidiscus has a similar arrangement of ambulacra, but the inter- 

 ambulacrals are highly imbricated. 



FOERSTEDISCUS SPLENDENS, n. sp. 



Plate 7, fig. 13 



The theca, a depressed semiglobose sack about 3 cm in diameter 

 resting upon a limestone layer, is very similar to the genotype in its 

 general characters but differs decidedly in the greater length of its 

 much more curved ambulacra, which in addition have more numer- 

 ous plates in each row. The anal pyramid also differs in that here 

 it is a narrow elevated tube instead of a flat broad area of small 

 plates as in F. grandis. 



The type specimen, a splendid example of these rare fossils, col- 

 lected by Irving G. Reimann, was obtained for description through the 

 courtesy of Dr. C. R. Stauffer, of the University of Minnesota. 



OccurretKC. — Black River (Decorah shale, top of Rhinidictya bed), 

 Ford plant, St. Paul, Minnesota. 



Holotype.— U.S.N. M. no. S-4079. 



FOERSTEDISCUS PARVUS, n. sp. 

 Plate 2, figs. 6, 7 



This species, represented by a dozen examples all exactly similar 

 to the two cotypes figured, differs from the genotype in the small 

 size of the theca, about 6 mm in diameter, the general delicacy of its 

 parts, and the more imbricating nature of its interambulacral plates. 

 The strongly curved ambulacra all directed to' the right, and the anal 

 area composed of small irregularly arranged plates, are generic 

 features common to the two species. 



Occurrence. — Trenton (Hull formation), Kirkfield, Ontario. 



Cotypes.— U.S.N. M. no. S-^ 



PYRGOCYSTIS Bather, 1915 



This genus, introduced here for sake of completeness, is described 

 and its component species listed in our 1935 paper. The theca is a 

 high cylindrical turret of overlapping plates surmounted by the oral 

 surface with five broad straight ambulacra. 



HEMICYSTITES Hall, 1852 



The writer has shown that this genus, usually associated with the 

 structure shown in Cincinnatidiscus {Agelacrinus) stellatus (Hall), 



