ECHINODERMATA. 211 



SUBKINGDOM ECHINODERMATA. 





THIS Subkingdom is represented, in the Palaeozoic rocks, by the Classes 

 Crinoidea, Stellerida, and Echinida. 



The word "Crinoidea" was first used in 1821, by J. S. Miller, who pub- 

 lished a book entitled "A Natural History of the Crinoidea." He used it as a 

 family name, but later investigations raised it to the rank of a Class. The 

 Palaeozoic Orders, into which the Class is divided, are Palseocrinoidea, Blastoidea, 

 Cystoidea, Lichenocrinoidea, Agelacrinoidea, Cyclocystoidea and Myelodactyloidea. 

 The Stellerida are represented by the Orders Asteroidea and Ophiuroidea, and the 

 Echinida by the Order Perischoechinida. 



The fossils consist of plates, variously arranged and connected, all of which are 

 composed of peculiar crystalline lime. The principal parts of the Palseocrinoidea 

 are the calyx or body, arms, pinnules, column, and base or root. The Agelacrinoidea 

 and Lichenocrinoidea were attached, by one side, to some foreign substance. The 

 Cyclocystoidea were free or attached in like manner. Whether the Myelodacty- 

 loidea were free or attached to other bodies is unknown. Some of the Cystoidea 

 were sessile, others possessed columns tapering to a point, and others had bases or 

 roots for attachment. The Blastoidea possessed columns, but whether or not any 

 of them attached by bases or roots is unknown. All Palseocrinoidea had columns, 

 but some did not have bases or roots. The Orders bearing pinnules are the 

 Blastoidea, Palseocrinoidea, and part of the Cystoidea. 



Prof. Wachsmuth has claimed the construction of the vault affords good 

 characters for the separation of the Palseocrinoidea into families, and has dis- 

 tinguished three plans upon which the summit is constructed, viz.: 



1. The summit composed of a more or less pliable, sometimes perhaps 

 squamous integument, yielding to motion, in the body and arms. 



2. The summit composed of solid plates, with a porous ventral sac, located 

 posteriorly, on the disk, and closed at the top. Anal opening rarely observed, but, 

 probably, lateral. 



3. The summit composed of heavy immovable plates, closely joining and form- 

 ing a dome arching the entire oral side. Anal opening directly through the wall of 

 the dome or at the extremity of a tube, the so-called proboscis. 



Without underestimating his work, a single illustration will show that families 

 can not always be distinguished by the construction of the vault ; for in the family 

 Heterocrinidse, there is no resemblance between the vaults of Ectenocrinus, 

 Heterocrinus, locrinus, and Ohiocrinus. Ectenocrinus has no tube or proboscis, 

 Ohiocrinus has a large spiral tube, and locrinus has a long cylindrical one, extending 

 beyond the ends of the arms and flowing pinnules. 



We believe the separation of the Palseocrinoidea into families must be based 

 upon the construction of the calyx and vault, but chiefly upon the former. Prob- 

 ably no family should be made to include genera, some of which have subradials 



