396 THE VOYAGE OF H.M.S. CHALLENGER. 
syzygy below the fiftieth node ; but it lies along the cable by the next éleven internodes, 
and is more or less attached to it by means of the cirri. 
The variation in the development of the basals in Pentacrinus decorus is most 
extraordinary, and shows what little reliance is to be placed on the characters of this part 
of the calyx for systematic purposes. In young specimens they are generally quite small 
and inconspicuous, appearing only as little triangular knobs or rhomboidal pieces which 
are sometimes just in contact by their lateral angles (PI. XXXV. fig. 1). But they do 
not stand out at all from the general plane of the calyx, and simply appear as continua- 
tions of the interradial ridges of the top of the stem upon which they rest. In older 
and even in adult individuals they may retain this condition (Pl. XXXIV. figs. 1, 8; 
Pl. XXXVI. fig. 3); while in others which are still premature they are a little more pro- 
minent (Pl. XXXYV. fig. 2); and when a large series of specimens is examined all stages 
are traceable between this condition and that of the individuals represented in Pl. XXXVI. 
fig. 1, and Pl. XXXYVII. figs. 1, 2. These have large rhomboidal basals, meeting one 
another laterally in the re-entermg angles of the calyx and standing out as prominent 
knobs which sometimes extend beyond the interradial ridges of the stem.!. A somewhat 
similar though less extensive variation in the development of the basals occurs in the 
fossil Antedon scrobiculata from the Brown Jura. 
The ray-divisions of Pentacrinus decorus are exceedingly variable. I have met 
with one case in which the number of three radials, so constant throughout the majority 
of the Neocrinoids, is considerably exceeded. The radial axillary is primitively the 
seventh joint above the basal ring, i.e., it is itself a syzygial jot and there are five 
below it, including the primary or first radials. The second and third of these five 
jomts are united by bifascial articulation, just like the ordinary second radials and 
axillaries of this species; and in this respect therefore this aberrant form differs from 
the type represented by Metacrinus, in which the second and third joints of the ray are 
always united by syzygy, whether the axillary be the fifth or eighth in the series of 
primitive radials (PL XXXIX. fig. 1; Pl. XLVI). 
One young specimen of Pentacrinus decorus which was brought by Sir Rawson 
Rawson from Barbados has only ten arms, as is the case in Pentacrinus naresianus ; 
while in another dredged by the “ Blake” there are only eleven, one of the primary arms 
dividing on the fifth jomt (PI. XXXV. fig. 1). A third individual (Pl. XXXV. fig. 2) 
has two arms on each of four rays ; but on the fifth ray one of the primary arms divides 
and one of the secondary arms so formed divides again, so that there are twelve in all. 
Other examples agai may have distichal series developed with considerable regularity 
all round the calyx, and occasionally also one or more palmar series as well (Pl. XXXVI; 
Pl. XXXVIL fig. 2). But the total number of arms rarely exceeds twenty-five in all; 
1 In the specimen represented in Pl. XXXVI. some of the first radials are considerably distorted, apparently as 
the result of injury and subsequent regeneration. 
