270 THE VOYAGE OF H.M.S. CHALLENGER. 
Family Pentacrinip&, d’Orbigny, 1852. 
Calyx small relatively to the stem and arms, composed of five basals and five radials, 
with under-basals in one genus. The rays divide from one to eight or ten times. The 
stem bears verticils of cirri at intervals. Two joints are united by syzygy at each node, 
to the upper one of which the cirri are articulated. The internodes are traversed by five 
ligamentous bundles which are interradially disposed and give rise to a more or less 
petaloid figure on the joint-faces. No root nor radicular cirri. 
Remarks.—Although definitions of this family have already been given by d’Orbigny, 
de Loriol, and Zittel, they have been based almost entirely upon palzeontological knowledge, 
and have not therefore given sufficient prominence to the syzygies between certain of the 
stem-joints, and to the ligamentous structures which produce the well known petaloid 
markings on their faces. The regular verticillate arrangement of the cirri along the whole 
length of the stem is especially characteristic of the Pentacrinide among the Neocrinoids, 
though there are a few Palzocrinoids, eg., Belemnocrinus florifer, in which this peculiarity 
presents itself. But it does not necessarily follow that the nodal joints in the stems of 
these older forms are the epizygals of syzygies, as is the case in the Pentacrinide. 
The same may be said of the so-called Encrinus beyrichi, in which Picard has described 
a verticillate arrangement of the cirri on the stem, without mentioning the presence of 
any syzygies at the nodes.? 
In Apiocrinus and Bourgueticrinus the upper part or even the whole of the stem is 
entirely free from cirri; and even when they do occur in verticils, it is only by two at a 
time instead of by fives, as in all the recent Pentacrinide except the one species Penta- 
crinus alternicirrus (Pl. XXV.; Pl. XXVIL. figs. 1-3). Further, there is nothing like a 
syzygy between the two joints forming a node in a Bourgueticrinus-stem, which are 
articulated to one another in the usual way. 
It is in fact the characters of the stem, much more than those of the calyx, which 
constitute the special distinctive mark of the Pentacrinide. For although Hxtracrinus 
is known by its under-basals, the composition of the calyx is identical in Millericrinus 
and Pentacrinus, and also in Metacrinus, if we follow strict morphology and consider 
the second radials as really arm-joints. 
The calyx of Balanocrinus is unfortunately not yet known. The genus was founded 
by Agassiz for a fragment in the Basle Museum, which he supposed to be a peculiar form 
of calyx. But de Loriol’ has shown that “ce prétendu calice n’est qu'un fragment de 
tige attaqué et deformé par un parasite.” Agassiz had, however, referred the stems 
associated with it to Pentacrinus subteres; and de Loriol, finding that the stem-joints of 
1 Ueber eine neue Crinoiden-Art aus dem Muschelkalk der Hainleite bei Sondershausen, Zeitschr. d. deutsch. geol. 
Gesellsch., Jahrg. 1883, p. 201. 
2 Swiss Crinoids, p. 163. 
