STAURASTEUM. 95 



I. Dorsal margin of the semi- 

 cell less convex than the 

 ventral ; semicells more 

 or less cup-shaped. 

 ! Processes straight, aris- 

 ing from the upper 

 angles of the cell. 



130. St. polymorphum. 



131. St. ciffine. 



132. St. proboscidium. 

 115. St. crenulatum. 



133. St. margaritaceum. 



134. St. Chavesii. 



!! Processes strongly in- 

 flexed. 



135. St. cyrtocerum. 



136. St. bmchycei'iun. 



137. St. eboracense. 



II. Dorsal and ventral margins 

 almost equally convex : 

 semicells subfusiform. 



138. St. hexacerum. 



139. St. Haaboeliense. 



b. Faces of seniicell provided with large and 

 prominent verrucse, often flattened 

 and complex, either on a central 

 protuberance (in the biradiate forms), 

 or in definite series. 



140. St. Cerastes. 



141. St. anatinum. 



142. St. sexcostatum. 



143. St. natatof. 



144. St. irregulare. 



Cells in vertical view usually 5-9 rayed, pro- 

 cesses nearly twice as long as the ' body ' 

 of the cell is broad, and radiating like the 

 spokes of a wheel. 



145. St. Arachne. 



146. St. Ophiura. 



147. St. verticillatum. 



148. St. Archeri. 



Cells 6 times as long as broad, excluding the 

 processes. 



149. St. elongatum. 



tf Cells with 2 processes at each angle, all lying in the same 

 horizontal plane. 



150. St. barbaric utit. 



