Crinoidea, Pentacrininae. ei 
it. The flush area may be smooth or granular. In the latter case the granules may 
be distinct or concresced, It is the complete concrescence of the granules that pro- 
duces the raised area. The concrescence of granules may be confined to a rim close 
round the lumen, and this rim may be circular or pentagonal, with angles either radial or 
interradial, 
Between the central area and the periphery a varying smount of space is occupied 
by the rosette, composed of five petals, each petal symmetrical about an interradius, 
and consisting of a median floor surrounded by crenellae. The floors are usually 
flush with the general level of the joint-face and with the bottoms of the grooves between 
the crenellae, but may be depressed below that level, especially in their centres; in 
adradial crenellae II floor 
/perradial crenellae 
4 ; ‘\ 
radial space \, \ 
peripheral 
mes -crenellae 
I 
Il 
rebate ~~ 
ue crenellae 
confluent 
lumen central area 
Text-figure 3. Diagram of three sectors, numbered I, Il, III, of the joint-face of a Pentacrinine internodal. 
Lumen pentagonal; central area raised, showing above its formation from concresced granules; floor 
depressed in sector I, flush in II, raised in III; radial ridge-group between sectors II & III consists of 
inosculating crenellae, that on the other side of III consists of gable-shaped crenellae ; the radial ridge- 
group on the lower side of sector I is of Ba/anocrinus type. 
rare cases they are slightly raised above that level. They mark the positions of the liga- 
mentar strands on which the internodals are threaded; they might be called ligament areas 
were they not also traceable at the syzygies, where the strands do not pass. The crenellae 
round each floor tend to lie at right angles to its outline; the adcentral crenellae may 
merge into the granules of the area when such are present; those lying along the sides of 
any petal and not reaching the periphery may be called the adradial crenellae; those 
which reach the periphery are peripheral crenellae. The adradial crenellae of one petal 
may be separated from those of the adjacent petal by a radial space. In Pentacrinus 
(s_ str.) this is a large triangle, with its apex at the central area and its base on the 
peripheral rim. In Tsocrinus a radial triangle may be present, but it never comes so close 
to the centre; or, on the contrary, the radial space may be restricted to a narrow radial 
groove, which combines with the corresponding groove of the adjacent joint-face to form 
