144 THE VOYAGE OF H.M.S. CHALLENGER. 
Switzerland ; though 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 Comatule. Many 
of the Jurassic species combine in a singular degree various characters which are of 
considerable value for the generic determination of recent Comatule. 
Besides their tendency to combine the characters of recent generic types, the 
Jurassic Comatulz 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 Comatulze 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 from 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 Comatulide neither Promachocrinus nor Thaumatocrinus 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. geol. Gesellsch., Jahrg. 1878, p. 66. 
