74 



crinus. The species is nearer Actinocrinns than Saccocrinns and 

 is best retained, in the genus, to which it was first referred. It 

 cannot be considered as a connecting link, until a way is found, 

 to pass through the Devonian System and Chouteau Group. Two 

 species of Cylicocriniis have been described and the specimens 

 are small. Fifteen species of Saccocrinns have been described, 

 varying greatly in size, but S. urnijormis and S. marcouamis have 

 the largest bodies belonging to any species, in the Aciinocrinidm. 

 There are ten ambulacral openings to the valt in Cylicocriniis, but 

 whether or not the arms bifurcate after becoming free is unknown. 

 In Saccocrinns there are either ten or twenty ambulacral openings 

 to the vault, and the arms, in Saccocrinns sjieciosus are known to 

 bifurcate twice after becoming free, giving to that species forty 

 arms, and, in other cases, where there are twenty ambulacral 

 openings, the arms are known to bifurcate once so as to give the 

 species, at least, forty arms. 



The Devonian genera are Genna;ocrinus, 3fe[jistocrinns aud the 

 species described by Hall from the Hamilton Group as 

 Aclinocrinus prcecursor, which may be a Batocrinus. There are 

 seven speceies of Gennaescrinus, and, in those species, in which 

 the arms have been described, there are sixteen, twenty, thirty 

 and forty arms. None of the species have large bodies. There 

 have been twenty-five species of Megistocrinus described. They 

 are generally large, ranking next to Saccocrinns, though quite 

 variable, in size; but there is great uniformity, in ihe general 

 shape of the different species. This genus occurs in ditfereut 

 Groups of the Devonian System and in the Kinderhook and Bur- 

 lington Groups of the Subcarboniferous. It is the only genus, in 

 this family, that is known to pass from one geological system to 

 another. The arms of the various species are, generally, unknown, 

 some of them, probably, bifurcate and others do not. The ambu- 

 lacral openings to tlie vaxdt, in some of the species, cannot be 

 determined from the imperfect descriptions that have been written, 

 and there is doubt about others. Among the Devonian species, 

 the number of ambulacral openings to the vault, that are definitely 

 known, are ten, fourteen, sixteen, seventeen, twenty, twenty-seven and 

 thirty, and in the Kinderhook and Burlington Groups ten and 

 twenty. The prevailing Devonian species have sixteen ambulacral 

 openings, a number thus far unknown, in the Subcarboniferous. 



