platycrinid^e. — cyathocrinus. 65 



Synonymes and References. 

 Cyathocrinus niammillaris Phill. Geol. York. PI. 3. f. 2. 



Formation and Localities. 

 Mountain limestone, BoUand; Mendips. * 



All the plates in this species are finely granulated, or delicately striated as in figure 

 8, /, and the excavations for the articulations of the rays are rather large. 



All the rays of the Cyathocrini which we have examined, appear to be, as far as 

 their imperfect preservation shews, composed of single series of joints. 



In the C. conicus the aperture through the dorso-central plates communicating with 

 the columnar canal is pentagonal. 



Observations on the Genus Cyathocrinus. 



Of the numerous genera into which the Crinoidea has been divided by different 

 Authors none has fallen into greater confusion than the Cyathocrinus. This is chiefly 

 owing to the system which has been to extensively followed, of giving specific names to 

 imperfect fragments of columns, which fragments, though varying in structure, may 

 not unfrequently be only different portions of the same column. 



It must be remembered that almost every column presents very different modifications 

 in form and structure according to its position with respect to its base of attachment. — 

 As a prevailing, though perhaps not constant rule, it may be observed that the inferior 

 portion of a column is most frequently composed of joints of equal thickness, while the 

 middle parts present a different modification, and the superior portion departs still 

 further in structure from the lower part. Thus a column may furnish materials for at 

 least three species, if every isolated fragment is to receive a specific name. Nor can 

 the central perforation always furnish good evidence of species, for it is sometimes 

 pentagonal in one part and circular in another. The alteration in structure caused by 

 the periodical growth of the column, may also prove another source of error. 



It is remarkable how seldom the columns which are found associated in the same strata 

 with the bodies of crinoids, have been referred to the species with which they are 



