Crinoidea, Pentacrininae. 
25 
c o n c a v i-s t e 11 a t e, i. e. when the re-entrant angles are merged in concave curves ; 
or (li) quinquelobate, i. e. when the re-entrant angles are bounded by convex curves 
continuous with those rounding off the interradial angles. Briefly, then, the section may be 
(«) a circle, ( b ) a laterally flattened circle, (c) a pentagon, (d) a rounded pentagon, 
(e) a star, ( f) a rounded s t a r, ( g ) an excavate s t a r, or ( h ) a pentapetalo n. 
The union or plane of union between two columnals is a j o i n t, and the apposed 
surfaces of the columnals are joint-faces. The whole outer surface of a columnal is 
the side-face, and is thu.s distinguished from the side of the pentagon or star. In a 
series of joined columnals, the lines along which the joints cut the side-faces are called 
suture-lines; originally such a line was termed a suture, but this term has been 
extended to mean a kind of joint. 
Columnals are divided iiito n o d a 1 s, which bear cirri ; and internodal s, which 
lie between them. In every stem, at any rate in its inore proximal region, it is possible to 
distinguish columnals of different sizes, representing as many stages of growth : the nodals, 
which are the first to be formed, are always the largest, and may therefore be described 
as columnals of the First Order or, more briefly, I columnals; those next formed, 
and therefore the next in size, are columnals of the Seeon d Order or II columnals; 
continuing, we distinguish a Third Order or III Columnals, a Fourth or IV 
columnals, and so on. The distinction in size between columnals of the several Orders 
a b c d e f g h 
Text-figure 1. Transverse sections of the Pentacrinine Stem. 
is always more obvious in the proximal region, while in the distal region it may vanish 
altogether, at least so far as the internodals are concerned. In the Pentacrininae the 
height of a columnal (i. e. the vertical measurement of its side-face) is always less than 
its diameter, and increases with age more slowly than does the diameter. Thus the relative 
height of the columnals decreases with age. 
The columnal immediately proximal to each nodal has been distinguished by P. H. 
Carpenter as a supranodal, and that distal to each nodal as an i n f r a n o d a 1. Each 
nodal is united to its infranodal by a rigid but brittle joint called a syzygiu m or syzygy. 
With reference to this joint, the nodal is termed epizygal, and the infranodal hypo- 
zygal. These terms are particularly useful in distinguishing the surfaces that meet at the 
syzygy. 
Nodals or epizygals are. always marked by cirrus-facets and are nearly always s w o 11 e n 
(i. e. obviously of greater diameter than the adjacent columnals) especially at the interradial 
angles, but are often more excavate in the re-entrant angles. Portions of the nodal cirrus- 
facets may extend on to either the infranodal or the supranodal ; and those columnals may 
then share in the modification of the nodals. Apart from this, a median vertical section of 
a columnal may have the sides s t r a i g h t (ft, b), or convex (c), or, rarely, concave ( d). 
For the sake of brevity, these terms may be applied directly to the side-faces (text-fig. 2). 
If the side-faces be straight and the transverse section circular, then the internode is cylin- 
d r i c a 1 (ft). If the side-faces be straight and the section pentagonal, then the internode 
is basaltiform ( b ). If the side-faces be markedly convex, and the section circular, then 
