: 
REPORT ON THE CRINOIDEA. 285 
This would give the maximum number of arms as forty ; but although the ten distichal 
axillaries may all be present, the palmar axillaries are frequently only developed on the 
two outermost of every set of four secondary arms, as in the unique specimen of Penta- 
crinus maclearanus (Pl. XVI.), and the individual of Pentacrinus alternicirrus shown in 
Pl. XXV. This would give six arms on each ray, making thirty in all. Sometimes, 
however, there are no palmars at all, or only one or two series of them (Pl. XVIII. fig. 2; 
Pl. XIX. figs. 1, 6, 7), so that the number of arms varies between twenty and thirty. 
The ray-divisions of Pentacrinus decorus present almost as much variation as the 
basals do. Some young specimens have only one or two distichal series (Pl. XXXV.); 
while one individual has but ten arms like Pentacrinus naresianus. In others, again, the 
arms are more numerous, though palmars are rare (Pl. XXXVI fig. 1). I am inclined 
to suspect, from an examination of several young specimens, that the many-armed 
condition is to some extent a secondary one. Thus if none of the arms were broken 
and subsequently repaired, the original of Pl. XXXYV. fig. 1 would have grown up with 
no more than eleven arms. When, however, an arm is broken off at a syzygy, and a new 
one developed in its place, an axillary is nearly always formed in this new one sooner 
or later, whether there were one present on the original arm or not. An instance of 
this kind is shown in Pl. XXXVI. fig. 2; and it is not uncommon to meet with indi- 
viduals of ten-armed species of Comatula which have replaced some of their arms after 
fracture and have developed axillaries in the reparation, so that the number of arms may 
reach eleven or twelve. This inerease in the number of arms after reparation seems to take 
place largely in Pentacrinus decorus ; for it is rare to meet with a specimen which does 
not show these signs of reparation, certain axillaries and the arms which they bear being 
distinctly smaller than their fellows. 
In Pentacrinus asterius and Pentacrinus miilleri there are always twenty arms or 
more, all the primary arms ending in distichal axillaries. Most of the secondary arms bear 
palmar axillaries, and there are sometimes even one or two more beyond these, so that 
the rays may divide five times in all. There is no special regularity of division in 
Pentacrinus asterius, though the number of arms is large, exceeding one hundred, 
according to Sir Wyville Thomson.’ But in Pentacrinus miilleri there are usually not 
more than four ray-divisions, the (palmar) axillaries beg limited to the outer arms as in 
Pentacrinus maclearanus and Pentacrinus alternicirrus; while the fourth and fifth 
axillaries, if present, occupy a similar position, so that there are six, eight, or ten arms to 
the ray, as 2,1; 1, 2—2,1,1; 1,1,2—or 2,1,1,1; 1,1,1, 2. 
The arms of Metacrinus branch as a rule more freely than those of Pentacrinus, except 
Pentacrinus asterius, all of the species having two, and most of them four axillaries 
beyond the radials; but there is no special regularity about the grouping of the arm- 
divisions. 
1 Sea Lilies, The Intellectual Observer, August 1864, p. 5. 
