144 THE VOYAGE OF H.M.S. CHALLENGER. 



Switzerland ; thougli both the other two genera range back as far as the inferior Oolite, 

 Antedon being much the more common. But the distinctions between them, so far as 

 can be made out in the calyx alone, are much less sharp than in recent Comatulse. Many 

 of the Jurassic species combine in a singular degree various characters which are of 

 considerable value for the generic determination of recent Comatulae. 



Besides their tendency to combine the characters of recent generic types, the 

 Jurassic Comatulse are remarkable for their large size, as are also the Cretaceous species. 

 The centro-dorsal may reach from 9 to 13 mm. in diameter, which is greater than that of 

 nearly every recent species except Antedon eschrichti ; while this type and Actinometra 

 robusta are almost the only living Comatulae with arm-bases anything like as massive as 

 those of the fossil species. Some of the Cretaceous forms must have been very large. 

 Thus the united centro-dorsal and radials of Antedon campichei {rom the Neocomian of 

 Switzerland may reach 15 mm. in height and over 20 mm. wide; while several 

 centro-dorsals of Antedon from the Upper Chalk are almost equally gigantic. 



The Eocene fossils are of moderate size ; but the Miocene Antedon rhodanicus has a 

 centro-dorsal 13 mm. in diameter, while the three species described by Forbes from the 

 Coralline Crag of Sutton are all considerably smaller. 



Of the remaining Comatulidse neither Promachocrinus nor Tliaumatocrmus has yet 

 been found fossil ; and though specimens have been described from the Maestricht Chalk 

 with a complete basal ring,^ I should hesitate at present to refer them to Atelecrinus. 



1 Zeitschr. d. deutsch. yeol. Gesellsclo., Jahrg. 1878, p. 66. 



