REPORT ON THE CRINOIDEA. 7/ 
be a permanent inequality, large and small joints alternating all down the stem. This is 
the case, for example, in the fossil Pentacrinus jaccardi and Pentacrinus nicoleti figured 
by de Loriol,t and also to some extent in the recent Metacrinus moseleyi (Pls. XLV., 
DaGY I): 
There is very little difference between the upper and the under faces of the young 
nodal joints, or between either of them and the ordinary internodal joint (Pl. XXII. 
figs. 1, 6-8, 15; Pl. XXXa. figs. 2, 3; Pl. XXXVII. figs. 14-16; Pl. LI. figs. 2-5). 
But as the jomts become older and more pentagonal their differences are more apparent 
(PL XIIL figs. 2, 3, 5,6, 10; Pl. XXII. figs. 16-18; Pl. XXXVI. figs. 11-13, 17, 18); 
while in the lower part of the stem the simple syzygial nature of the under face of the 
nodal jot and its loss of the denticulate petaloid markings become very distinct 
(EE SSVeotie G5) Bl XX figs, 19, 20; Pla XXVI. figs. 13, 14; Pl, XX VIL fies. 2.3; 
PL XXX. figs. 26, 27; Pl. XXXVII. figs. 21, 22; Pl. XXXIX. figs. 4,5; Pl. XLV. 
figs. 4,5; Pl. L. figs. 21, 22). 
In some species of Pentacrinus, e.g., Pentacrinus wyville-thomsoni, the lowest and 
therefore the oldest stem-joints gradually lose the more or less prominent ridges which 
appear on the faces of those higher up the stem, and become much more smooth and 
simple in their character (Pl. XXII. figs. 23-26). 
A similar change seems to take place in Pentacrinus asteria (Pl. XIII. figs. 10, 11), 
and also in other species, though I have not been able to trace it so distinctly as in 
Pentacrinus wyville-thomson. It is manifested externally by the gradual disappearance 
of the crenulation of the interarticular lines, which is so very prominent in the upper and 
middle parts of the stem (Pl. XIII. figs. 7, 8; Pl. XV. figs. 1, 2, 4; Pl. XIX. figs. 2-5; 
REE PELE XXVIL fig, 15) Pl XOX. fig. 3 yp Pls. XXXV.-XRAKVIT; Plo ee 
fers aelly Sek Or;) Ble NUTT. fig: 1). 
The amount of crenulation varies considerably in different species, according to the 
position of the large teeth bordering the outer ends of the petaloid spaces. When these 
start from near the edge of the joint, as in Metacrinus cingulatus, Metacrinus nobilis, or 
Metacrinus costatus (Pl. XLI. figs. 1-3, 5-7 ; Pl. XLIX. figs. 3-5), the interarticular line 
is well crenulated. But there is sometimes a sort of rim outside the ends of the teeth, as 
in Metacrinus murrayt and Metacrinus varians (Pl. XLI. figs. 15, 17; Pl. XLVIL. figs. 
6-9), and the external crenulation is then less marked. This outer rim is only formed 
comparatively late, the teeth of a young joint starting directly from its edge, as is well 
shown in Pls. XXII., XXIII., and XX XVII. 
The increase in the length of the internodes only takes place gradually, and pari 
passu with the continual formation of new joints just below the calyx. Hence, in the 
upper part of the stem, there is a variable number of premature internodes, those nearest 
the summit being the shortest, and consisting of the smallest number of joints. The 
1 Swiss Crinoids, pp. 130, 140, pl. xv. figs. 13, 36, 
(ZOOL. CHALL, EXP.—PART XXx11.—1884.) 3 
