NO. 8 EDRIOASTEROIDEA BASSLER 3 



WALCOTTIDISCUS, n. gen. 



Pentagonal form and general shape of theca as in Stromatocystites, 

 but the oral face bears curved ambulacra, four (1-4) directed to the 

 left and one (5) to the right. Furthermore, the edge of the oral sur- 

 face is composed of a narrow band of very small nodose plates and 

 the under side of larger polygonal plates imbricating. Anal area 

 indistinct. 



Genotype. — W . typiealis, new species. Middle Cambrian of British 

 Columbia. 



WALCOTTIDISCUS TYPICALIS, n. sp. 



Plate I, fig. I 



Type specimen, free, depressed, globular, subpentagonal in outline, 

 imbedded and somewhat distorted in hard shale. Oral face with five 

 slightly curved ambulacra, four directed to the left and one, the right 

 posterior, to the right, separated by polygonal interambulacral plates 

 very slightly overlapping. Edge of oral side formed by a band con- 

 sisting of five or more rows of very small elongate imbricating plates ; 

 basal side of theca as shown where pushed over oral face, occupied 

 by large elongate polygonal, imbricated plates. Anal area not dis- 

 tinguishable with certainty. 



Occurrence. — Burgess shale of Middle Cambrian, Burgess Pass 

 near Field, B. C. (loc. 35 k). 



Holotype. — U.S.N.M. no. 90754. 



CYSTASTER Hall, 1871 

 (Tliccocystis Jaekel, 1899) 



Theca an elongate sack with the lower end attached to some foreign 

 object. Ambulacra short and straight, five in number, with plates 

 often rather nodose. Interambulacrals rounded or polygonal, mosaic, 

 very minute (0.25 mm in diameter). Anal pyramid of 10 elongated, 

 abruptly raised plates. 



Genotype. — Hemicystites (Cystastcr) granidatus Hall, 1871. Or- 

 dovician (Maysville) of Ohio. 



CINCINNATIDISCUS, n. gen. 



(Hemicystites of authors not Hall) 



Like Gystaster except that the theca is not sacklike but depressed, 

 attached, and that the interambulacral plates are squamose and imbri- 

 cate distinctly, divided into larger central plates and a marginal zone 

 of small nodose ones. Anal pyramid of nodose plates. 



