1881.] NATURAL SCIENCES OF PHILADELPHIA. 231 



size of the plate, and the comparatively large space which it occu- 

 pies in the body; but too much importance should not be attached 

 to it, as we find in the Actinocrinidaa and Rhodocrinidse the same 

 variation, and apparently without anj^ disturbance of the relations 

 between the genera. The presence of this plate in the Platy- 

 crinidjB is entirely in harmony with our idea that this group 

 represents a younger stage of the Actinocrinidoe, for this anal 

 plate was early developed in the animal, and is found in the 

 youngest individuals in both groups of equal size with the first 

 radial. 



In 1843, the two Austins proposed (Monogr. Rec. and Foss. 

 Crinoids) the name Platj'crinidae as a family designation, embra- 

 cing the genera Platycrinus, Gyathocrinus and Caryocrinus, 

 without special diagnosis, merely mentioning that those genera 

 " had but few plates below the ray, and thus might conveniently 

 be arranged into a natural group." They placed Marsupiocrinus 

 along with Crotalocrinus under the " Marsupiocrinoidea." 



Not any better is the arrangement of D'Orbigny, who placed 

 Platycrinus under " Melocrinidffi," and Edwardsocrinus and 

 Dichocrinus under the Cyathocrinidse. 



F, Roemer's " Platycrinidffi " (1855. Leth. Geognostica, Ausg, 

 III, p. 228), agree substantially with ours. He brought into the 

 family: Platycrinus, Dichocrinui^, Hexacrinus, CuUcocrinus and 

 llarsupiocrinus, but unfortunately added Atoc7^inus^ and Sym- 

 bathocrinus, the first of which we place under the Cyathocrinidae, 

 and the latter we consider the type of a new famil}-. Pictet 

 (Traite de Paleont., 1857) made his Platycriniens a sub-division 

 of the Cyathocrinidae and enumerates under it the genera Platy- 

 crinus, Edwardsocrinus^^ Amblacrinus,^ Ilarsupiocrinus, Ato- 

 crinus, Symbathocrinus and Adelocrinus* but placed Coccocrinus 

 and Haplocrinus under the Haplocrinidse, following Roemer. 



The arrangement of Zittel (Handb. der Palaeontologie) agrees 



^ Atocrinus McCoy, is evidently a Gyathocrinus in which the sutures 

 between the plates are invisible, owing to the condition of the fossil, and 

 not a Platycrinus as supposed by some authors. The plates of the body 

 and the arras agree exactly with Gyathocrinus, while no Platycrinus of the 

 Subcarbouiferous has single arm joints. 



^ Syn. of Platycrinus. 



^ D'Orbigny, insufficiently defined, probably syn. of Goccocrinus. 



* Phill., insufficiently defined. 



