PLATVCRINID.E. PLATYCRINITES. 



Family PlatycrIxMd.e. 



Contains the genera Platjjcrinifes, Cyathocrinites, and Carj/ocrinitcs. As these genera 

 have but few plates below the rays, they may be conveniently arranged into a natural 

 group. 



Genus I. Pl.\.tycrinites. (MiUer.) 

 Elijm. nAATYS, (Flatus) broad, with reference to the fonn of the perisoniic philes. 



Definition. — Dorso-central plate (pehds) undivided and pentagonal, fitom which fi^e, 

 and in one or two instances six, broad perisomic plates proceed. The dorso-central 

 plate is perforated centrally, to correspond with the opening in the column. Mouth in 

 some species lateral, in others central, and frequently elongated into a proboscis of 

 considerable length. Column composed of calcareous joints, either articulating by 

 diverging strise, or by transverse ridges. Base of attachment unknown, probably a hard 

 calcareous secretion, with fibres by which the animal attached itself to the bed of the 

 ocean. 



Miller, in his Natural History of the Crinoidea, speaks positively as to the base of 

 attachment, but it is believed that no satisfactory proof exists of this portion of the 

 animal having ever been discovered. 



The various species hitherto ascribed to the genus Platycrinites, arrange tliemselves 

 naturally into three groups, the one characterised by the length, form, and jiosition of 

 the oral tube ; the second by the structiu-e of the valvate mouth ; and the tliird by the 

 mouth being placed laterally, or at some distance from the centre of the \'isceral cup. 



We are therefore inclined to consider that it may hereafter be desu'able to separate 

 this genus into three divisions. Those species with central elongated oral tubes, form- 

 ing one division, as the P. Icevis : those with central valvate unobtrusive mouths, or 

 mouths capable of being withdrawn into the visceral cup, a second, for which we would 

 propose the generic name of Centrocrhms : and those species Avith mouths placed 

 laterally, or not central, a third, which we woidd designate by the term Pleurocrinus. 



The genus Platycrinites has, imtil recently, been considered as peculiar to the moun- 

 tain limestone. Goldfiiss has, however, mentioned two species as occurring in the Eifel; 



