670 ECHINODERMATA. 



SUBKINGDOM ECHINODERMATA. 



CLASS CRINOIDEA. 



The only systematic classification of crinoids into families, so far as learning 

 has extended, is based upon the number and arrangement of the plates in the 

 calyces. See " The Structure, Classification, and Arrangement of American Palae- 

 ozoic Crinoids into Families," 16th Rep. Geo. Sur., Indiana, p. 302. The number 

 of basal plates is first in importance. There are no rudimentary basals. Second 

 in importance is the presence or absence of subradials. Third, the presence or 

 absence of regular interradials. Fourth, the structure of the azygous side. Fami- 

 lies having only two basal plates are confined to the Subcarboniferous and Car- 

 b6niferous. Those having three basals extend from the Lower Silurian to the Sub- 

 carboniferous. Those having four basals extend from the Lower Silurian to the 

 Devonian. And those having five basals extend from the earliest crinoids through- 

 out Palaeozoic time. 



Genera having Two Basals. 



Family Acrocrinid^e. — Acrocrinus. 



Family Dichocrinid.e. — Dichocrinus, Cotyledonocrinus, Talarocrinus. 



Family Pterotocrinedje. — Pterotocrinus. 



Genera having Three Basals, no Subradials, Regular Inter- 

 radials. 



Family Actinocrinid^e. — Actinocrinus, Agaricocrinus, Alloprosallocrinus, 

 Amphoracrinus, Batocrinus, Blairocrinus, Cylicocrinus, Dorycrinus, Eret- 

 mocrinus, Gennseocrinus, Megistocrinus, Physetocrinus, Saccocrinus, Stega- 

 nocrinus, Strotocrinus, Teleiocrinus. 



Family Arthracanthid^e. — Arthracantha. 



Family Dolatocrinid^e. — Allocrinus, Dolatocrinus, Hadrocrinus, Stereocrinus. 



Family Platycrinkle. — Coccocrinus, Cordylocrinus, Eucladocrinus, Macros- 

 tylocrinus, Marsupiocrinus, Platycrinus. 



Genera having Three Basals, Subradials, no Regular Inter- 

 radials. 



Family Ampheristocrinid^. — Ampheristocrinus, Closterocrinus. 

 Family Ichthyocrinid^. — Ichthyocrinus, Lecanocrinus, Mespilocrinus. 



Genera having Three Basals, Subradials, and Regular Inter- 

 radials. 



Family Taxocrinid^e. — Forbesocrinus, Onychocrinus, Taxocrinus. 



