SCHUCHERTIA STELLATA. 211 



8. laxata. — Larger form with longer arms. Apparently R may be over 

 30 mm. and nearly three times r. Adambulacralia as broad as the 

 infero-marginalia. Apical plates rather irregular and slightly tumid. 

 Upper Ordovician. 



8. ordinaria. — Form imperfectly known. Apical plates more spicular. 

 Basal Silurian. 



S. wenlocJci. — General form and size very similar to 8. laxata. Adam- 

 bulacralia much less prominent than the infero-marginalia. Apical 

 plates have become paxills. Middle Silurian. 

 A madreporite has not been identified in specimens of the first three species. 

 In 8. wenlocki it is large and on the oral surface (Text-fig. 154, p. 21 G). 



1. Schuchertia stellata (Billings). Plate XVI, fig. 8; Text-fig. 149. 



1857. Palasterina stellata, Billings, Geol. Surv. Canada, Rep. Progress for 1853— 185G, p. 209. 



1858. „ ,, Billings, Geol. Surv. Canada, Canad. Organic Rem., dec. iii, p. 76, pi. ix, 



figs. 1 a, 1 b. 

 1862. „ „ Wright, Mon. Brit. Foss. Echinoderm., Oolitic, vol. ii (Mon. Pal. Soc, 



vol. for 1861), pp. 26, 27, fig. 16 6. 

 1876. „ ,, Quenstedt, Petrefakteukunde Deutschlands, vol. iv, p. 74, pi. xeii, fig, 34. 



1900. Trentonaster stellata, Stiirtz, Verhandl. Nat.urh. Ver. preuss. Rheinl., Jahrg. 56, pp. 217, 



224, 225. 



1914. Schuchertia stellata, Schuchert, Fossiliuni Catalogus, Animalia, pt. 3, pp. 32, 43. 



1915. „ „ Schuchert, Bull. 88, U.S. Nat. Mus.. pp. 196—198, pi. x.xxii, fig. 2; 



pi. xxxiii, fig. 1. 



Material. — The holotype, which shows the oral surface, was found by 

 E. Billings, and is preserved in the Canadian Geological Survey Collection 

 (no. 1399) at Ottawa. A second specimen in the same collection shows the apical 

 surface. It was found on Governor General Bay, near New Edinburgh, Canada. 



Specific Characters. — See p. 210. 



Description. — The following description is given by Schuchert: 



"Abactinal area composed of a series of plates which are more or less closely 

 adjoining, and on the rays are arranged in distinct but twisted columns. This 

 twisting is due to the insertion of new columns of plates, always on the right side, 

 crowding the older ones to the left. The plates on the rays are subqundrangular 

 to elongate subquadrangular, increasing in size proximally, and on the disc are 

 largest and generally subcircular in outline, or faintly stellate. The plates appear 

 to be smooth. At the apex of the ray are two somewhat larger plates followed by 

 three columns, and on each side of this there are two other columns of ossicles. 

 Near the beginning of the interbrachial arcs the rays have from seven to eight 

 columns of plates. 



" Madreporite not distinguished among the abactinal plates. 



" Actinally the most conspicuous columns are the adambulacrals bounding the 



