REPORT ON THE CRINOIDEA. 25 
While the general characters of the stem are identical in Rhizocrinus and Bathy- 
erinus, there is a good deal of variation in its details, and especially in the mode of 
growth. 
In all cases the new joints are added at the top of the stem, immediately beneath 
the cup ; but the rate at which they increase in length is very different in the different 
species. It appears from Sars’s figures,’ and from my own observations, that the pro- 
duction of new joints in the stem of Rhizocrinus lofotensis is slow compared to their 
subsequent increase in length. For there are very rarely more than three joints beneath 
the cup which are wider than high, and even these have an appreciable thickness 
(Pl. IX. figs. 1, 2; Pl X. fig. 1). Sars remarks of the uppermost one that it is 
“annulaire et a 2 ou 3 et méme souvent 5 ou 6 fois plus de largeur que de hauteur ;” 
while there are usually not more than eight cylindrical joints beneath it. Below this 
limit the jomts have the well-known dice-box shape, with the characteristic terminal 
faces, the peculiarities of which begin to appear very few joints below the cup. 
Most individuals of Rhizocrinus rawsoni seem to be generally similar to Rhizocrinus 
lofotensis in these characters (Pl. IX. fig. 3; Pl. LIII. figs. 7, 8). But in one example 
I found five joints beneath the cup which were wider than high. The second and third 
are mere circular disks with perfectly plain faces like those of the fourth (Pl. X. fig. 10) ; 
and the faces of the newly formed joints of Rhizocrinus lofotensis which are figured by Sars? 
are of the same nature. But the uppermost joint of all is of a different character 
altogether (Pl. X. fig. 9). It has a pentagonal outline, and its surface, which rises 
gradually from the circumference towards the centre, is divided by five radiating ridges 
into an equal number of trapezoidal fossee that receive the lower ends of the elongated 
basals (Pl. X. figs. 3, 5). Here, therefore, we find the top stem-joint presenting the 
same characters that it does in Apiocrinus* and Millericrinus,‘ and entering to some 
extent into the composition of the cup, while the new joints are probably intercalated 
below it. Quenstedt°® speaks of this uppermost stem-joint in the Apiocrinid indif- 
ferently as “Endstiick, Endsiiulenglied, or Fiinfrippenglied.” De Loriol® has named it 
“article basal ;’ while Zittel’ speaks of it as the “ Centro-dorsal,” and remarks “ Dasselbe 
scheint, wie aus der Andeutung von Nihten hervorgeht, aus 5 urspriinglich getrennten 
Stiicken entstanden zu sein und entspricht wahrscheinlich den 5 Infrabasalpliittchen 
bei Encrinus.” It is perhaps a little expedient to employ the term “ centro-dorsal” for 
a joint which bears no cirri, as its similarly named homologue does in the Comatule. 
1 Mémoires pour servir 4 la connaissance des Crinoides vivants. 1. Du Rhizocrinus lofotensis, tab. i., ii. 
2 Op. cit., tab. ii., figs. 20-22. 
3 D’Orbigny, Histoire Naturelle, générale et particulitre des Crinoides vivans et fossiles., pl. ii. fig. 3, pl. iii, 
fig. 4, pl. v. fig. 4. 
* Ibid., pl. xiv. figs. 15, 23, 24; and Quart. Journ. Geol. Soc., vol. xxxviii. p. 33, pl. i. 
5 Eneriniden, pp. 314, 315. 
6 Swiss Crinoids, p. 4; Paléont. Frang., loc. vit., p. 19. 
7 Handbuch der Paleontologie. Palzozoologie, Bd. i., pp. 388-390. 
(ZOOL, CHALL, EXP.—PART xxxIr.—1884.) Ti 4 
