16 PLATYCRINID.i:. PLATYCRINITES. 



In the Ajnocrinites, and some other genera, we have satisfactoiy and certain evidence 

 of their having been attached to the bed of the ancient seas ; therefore, from analogy in 

 form, we may reasonably attribute the same pecnharity to other species wherein the 

 organic structure presents characters sufficiently similar to warrant the conclusion. 



Much confusion has prevailed respecting the P. Isevis, owing to several writers on the 

 Crinoidea having applied the specific name to specimens wholly and obviously specifically 

 distinct fi-om each other. The true P. lavis is, as its name imphes, perfectly smooth, 

 and may be known by the absence of all corrugating uneven surfaces, or granidse, on 

 any of the plates, either above or below the rays. When the proboscidial plates and 

 rays are absent, then a difficulty may possibly arise as to its identity; but the term l(evis 

 has been applied to crinoids with large pointed abdominal plates, and lateral mouths, 

 and which are quite dissimilar in the arrangement of the whole calcareous fi-ame work 

 above the rays. 



Mr. Phillips has fallen into this error, in his excellent Avork, Geology of Yorkshire : 

 but it is just to observe that he had himself some misgivings on the subject, for at page 

 204, we meet with the following remark : " It is very doubtful whether this be really 

 the sjjecies of Miller : the articulations of the scapidee do not quite agree." It might have 

 been added, with perfect truth, that none of the plates quite agree with Miller's figm-e. 



Miller, in his Natural History of the Crinoidea, enters into minute details relative to 

 the columnar joints occasionally presenting various peculiar appearances, such as 

 "slightly four cornered;" angles rounded, while along the middle of the exterior 

 circumference the intermediate muscle is pressed out and forms a smooth rim, which is 

 sometimes studded at intervals Avith tubercles occasionally elongated into a kind of 

 pointed feelers, giving the joint some resemblance to tlie rowel of a spur. 



All these apparently structural variations described by MLUer are frequently met Avith, 

 but they are merely the eff'ects of Aveathering, and are not at all confined to the Platy- 

 crinites, for precisely the same peculiarities are as frequently seen in the columns of other 

 genera, as in that to which Miller considered them peculiar. 



The same observations wiU equally apply to the irregularities sometimes met with in 

 the auxihary side arms, and Avhich Miller considered as indicatmg the muscularity of 

 their exterior integument : but Avhich are either attributable to the decomposition of the 

 calcareous skeleton previous to its becoming imbedded in the matrix, or to its subse- 

 quent exposure to the atmosphere, after the beds had become elevated, and Avere 

 gradually yielding to its corroding influence. These facts have been too frequently 

 observed to admit of the least doubt on the subject, and which facts an observation of 

 Miller's, in a great measure, tends to confirm. At page 77, Nat. Hist, of the Crinoidea, 

 the foUoAving remark occurs : " On the surface of the same mass of partially decomposed 

 limestone, I have met Avith very thin joints resembling those just described, only being 

 very small and much longer." 



