446 THE DEPTHS OF THE SEA. [CHAP. ix. 



the radial axillary originates a simple arm only from 

 one or both of its sides, thus reducing the total 

 number of the arms ; and sometimes one of the four 

 arms given off from the brachial axillaries again 

 divides, in which case the total number of arms is 

 increased. The structure of the disk is much the 

 same as in the species of the genus previously known. 



Two other fixed crinoids were dredged from the 

 ' Porcupine/ and these must be referred to the Apio- 

 crinida3, which differ from all other sections of the 

 order in the structure of the upper part of the stem. 

 At a certain point, considerably below the crown of 

 arms, the joints of the stem widen by the greater 

 development of the calcareous ring, the central 

 tube only increasing very slightly in width. The 

 widening of the stem joints increases upwards until 

 a pear-shaped body is produced, usually very elegant 

 in form, which, looking from the outside, one would 

 take for the calyx. It is, however, nothing more 

 than a symmetrical thickening of the stem, and the 

 body-cavity occupies a shallow depression in the top 

 of it included within the plates of the cup the 

 basals and radials which are thicker and more 

 solid than in other crinoids, but otherwise normally 

 arranged. The stem is usually long and simple 

 until near the base, where it forms some means of ' 

 attachment, either as in the celebrated pear-encrinites 

 of the forest marble, a complicated arrangement of 

 concentric layers of calcareous cement which fix it 

 firmly to some foreign body, or, as in the chalk 

 Bourguetticrinm and in the recent Rhizocrinm, an 

 irregular series of jointed branching cirri. 



The Apiocrinidae attained their maximum during 



