CPJNOIDEA. 285 



by the uppermost joint of the column, which is dilated to 

 form the so-called " centro-dorsal basin," and which carries 

 one 0* more whorls of short jointed pinnules or " cirri " the 

 homologues of the " side-arms " of Pentacrinus. In the calyx 

 itself the basals are generally comparatively large, and are 

 anchylosed with one another, and often with the primary 

 radials, to form the so-called "rosette." There are usually 

 three cycles of radials ; and the arms may retain their prim- 

 itive number of five, or may be once or twice bifurcated. 

 The most important fossil genus of the family is the Jurassic 

 Solanocrinus ; but the living Antedon has been detected in 

 the Tertiaries, and has been quoted, along with other genera, 

 from older deposits. As shown by Mr P. Herbert Carpenter, 

 the fossils of the Chalk known as Glenotremites consist really 

 of the united centro-dorsal piece and radial pentagon of a 

 Comatulid. The Jurassic genus Saccosoma (fig. 156), though 

 a free Crinoid, apparently allied to Comatula, is at present 

 but imperfectly understood. 



