PLATYCUINII).?;. PLATYCRINITES. 1 1 



highly probable, for we see something analogous to it in recent allied forms ; but that it 

 possessed sufficient contractile power to effect the movement of the rays wc consider as 

 quite improbable. 



The number of the rays, and closeness of the tentacula, ser^e as indices to denote 

 whether the animal's staple articles of food were minute or otliermse. The orcUnary 

 objects of sustenance to those criuoids -with few, but vnde spreadmg rays, must have been 

 of larger size than those creatures which supported the many rayed and closely tentacu- 

 lated species. These latter, by theu* densely crowded plumose rays, were enabled to 

 filter the element in Avliich they lived, straining it as through a sieve, thus separating 

 and retaining the mmute marine animalcida, which generally abound in sea water, 

 witliin the folds of their dcUcate tentacula ; while the former captured and ordinarily 

 fed upon such less minute species of animals as came AV'ithin the sweep of their mde 

 extended rays. 



The form of the proboscis seems to confirm these views of theii- alimentation; and it 

 may be considered as a general rule, though liable to occasional exceptions, that the size 

 of the oral tube and the nimiber of the rays bear a certain relation to each other. In 

 those species which have numerous rays and closely set tentacida, the diameter of the 

 oral tube is jiroportionally contracted ; while in those with but few rays it is much 

 enlarged. There is m reahty a remarkable comcidence, in this respect, in those species 

 wliich possess elongated mouths ; and it is evident that the relation between the organs 

 for seeming the food, and the form and size of the mouth is all but constant. 



INIiller and C'uvier have represented the rays of tliis species as consistmg of a double 

 series of joints from their jjoints of bifiu-cation. This is clearly erroneous, but the 

 smaUness of the specimen, from which the former took Ms figiu-e, will perhaps account 

 for his mistake. And the latter appears to have closely copied Miller's error. 



Column. — The column of this species is composed of numerous joints, wliich are 

 invariably cu-cular at, and near the point of attachment to the body, but as it recedes 

 fi-om it, the joints gradually assimie an elliptical form. This change in the structure of 

 the coliunn is highly interesting, for by it we imagine that, in conjunction with other 

 pomts of structm-e, it fru-nishes a clue by which we can arrive at a knowledge of the 

 manner in which the animal sought for and obtained its food. 



Though JliUer is not to be relied on, especially as regards the columns of the 

 Crinoidea, liis explanation of the remarkable change so generally observable in the 

 Platycrinites is exceedingly ingenious, and in some measure correct, he is therefore 

 justly entitled to the merit of being the first to remark on the singidar modifications 

 obsen able in the columns of this genus. 



The upper or circidar portion of the column is composed of largei- and smaller 



