294 THE VOYAGE OF H.M.S. CHALLENGER. 
(Pl. XXIV. fig. 9, 2co, cco). The canal in which this is lodged is never close down to 
the proximal openings in the inner or dorsal face, as it is in all Comatule, even Atele- 
crinus. But its position varies somewhat in different species. Thus, for example, it 
comes nearer to the edge of the central funnel in Pentacrinus decorus (Pl. XXXII. 
fig. 5) than in Pentacrinus wyville-thomsoni (Pl. XX. fig. 6). The double axial cords 
of the rays which proceed outwards from it resemble those of Comatulz in their very 
close approximation. Small portions of them, cut very obliquely, are seen in Pl. XXIV. 
fic. 9, A. They are lodged close together in the same canal as far as the axillary radial, 
not being so widely separated as in Enecrinus; and the arrangement of the commissures 
in the axillary is just the same as was discovered by Ludwig in the Comatule. 
D. The Geological History of Pentacrinus. 
Excepting for some doubtful forms from the Eifel, the earliest known Pentacrinidee 
occur in the ‘“ Wellenkalk” of the Jura, at an horizon somewhat lower than the well- 
known limestone in which Encrinus liliiformis occurs. According to Quenstedt, both 
generic types occur together in the Wellenkalk of Wiirtemberg; and he refers all the 
Pentacrinide to one species, Pentacrinus dubius, though they have received various 
other names, both generic and specific, from earlier writers. Nothing being known of 
them but fragments and isolated joints of the stem, any detailed classification of them 
is hardly possible. But the similarity of the stem-fragment from Waltershausen' with 
ten cirrus-whorls at intervals of eight or ten joints, to the stems of recent Pentacrinide, 
is very striking. This resemblance was noticed by von Schlotheim,’ who described the 
fossil as Pentacrinus vulgaris, and referred to the same type the recent specimens of 
Guettard and Ellis. Some years later Quenstedt’® gave an excellent figure of it; but in 
the absence of an associated calyx he hesitated to refer it to Pentacrinus as von 
Schlotheim and Goldfuss had done, and so described it as Encrinites dubius. Beyrich 
and later writers, however, have generally regarded it as a Pentacrinus, as Quenstedt 
himself has done in the Encriniden, and the reference of the fossil to the Pentacrinidee 
will now be scarcely disputed. Another very similar stem from the Muschelkalk of 
Silesia was described by von Meyer* as Chelocrinus acutangulus. This genus was 
established to receive certain forms with more than ten arms, owing to the presence 
of distichal and palmar series, which had been generally referred to Encrinus. It 
has been abundantly proved, however, by the researches of von Strombeck’ and others, 
1 Encriniden, p. 198, Tab. 97, figs. 14-22. 
* Die Petrefactenkunde, p. 327. 
5 Ueber die Encriniten des Muschelkalks, Archiv f. Naturgesch., Jahre. i. Bd. ii., 1835, p. 225, Taf. iv. fig. 2. 
* Fische, Crustaceen, Echinodermen und andere Versteinerungen aus dem Muschelkalk Oberschlesiens, Paleeonto- 
graphica, Bd. i., 1851, p. 272. 
® Ueber Missbildungen von Encrinus liliiformis, Lam., Paleontographica, Bd. iv., 1856, p. 176. 
