NO. 6 NEW AMERICAN EDRIOASTEROIDEA — BASSLER 25 



EXPLANATION OF PLATES 



Plate i 



(All figures after the respective authors of the species unless otherwise stated.) 



PAGE 



Fig. I. Edrioaster bigsbyi Billings 22 



Oral side of the flexible theca, natural size, with two rows of 

 covering and flooring plates, showing ambulacra passing to 

 aboral side (after Bather). 

 Trenton (Hull) : Ottawa, Ontario. 



Figs. 2, 3. Dinocystis barroisi Bather 22 



Top and basal views one-half natural size. All the ambulacra 

 curve strongly to the left and the aboral side is composed of 

 closely imbricating plates and has a small central orifice for 

 attachment. 

 Devonian: Condroz, Belgium. 



Figs. 4, 5. Discocystis (Agclacrinus) kaskaskieiisis (Hall) 21 



(See also pi. 3, figs. 4-6, pi. 7, fig. 11.) 



4. View, natural size, of ambulacral surface of a compressed 

 specimen. The direction of one of the ambulacra is in error and 

 has been corrected in ink. 



5. Holotype of Echinodiscus optatus Worthen and Miller, repre- 

 senting part of the aboral side of Discocystis kaskaskiensis com- 

 posed of numerous rows of fused imbricating plates and a 

 central area of attachment. 



Qiester : Kaskaskia and Polk County, Illinois. 

 Figs. 6, 7. Stromatocystites pcntangiilaris Pompeckj 3 



Drawings of oral surface showing ambulacral areas and of lower 

 side of theca with plated structure, slightly reduced. 



Middle Cambrian : Tegrovic, Bohemia. 

 Figs. 8, 9. CyatJwcystis plant iiiae Schmidt 23 



8. Lateral view of two individuals growing upon a pebble, natural 

 size. 



9. Sketch of oral surface, X 3, showing ambulacral areas with 

 covering plates in part removed, and the anal pyramid and fused 

 interambulacrals. Ordovician ( RchiuospJicritcs limestone) : 

 Riga, Esthonia. 



Fig. id. Cyathotheca siiecica Jaekel 23 



Top view of the cone-shaped theca, showing the pentagonal oral 

 surface and the apparently hidden ambulacra, slightly enlarged. 

 Ordovician of Sweden. 



Fig. II. Lebetodiscns {Agclacrinites) dicksoni (Billings) 9 



View, natural size, illustrating curvature of all the ambulacra to 



left, and large mosaic interambulacral plates. 

 Trenton (Hull) : Ottawa, Ontario. 

 Figs. 12, 13. Agelacrinites (Haplocystites) rhcna nus Roemer 16 



12. Mould of the underside of upper part of theca, natural size. 



13. Cast of same, enlarged, showing ambulacral flooring plates 

 in single rows. 



Devonian : Rhine area, Germany. 



