294 THE VOYAGE OF H.M.S. CHALLENGER. 



(PI. XXIV. fig. 9, ico, ceo). 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 Comatulse, even Atele- 

 crinns. But its position varies somewhat in different sjjecies. Thus, for example, it 

 comes nearer to the edge of the central funnel in Pentacrinus decorus (PI. XXXIII. 

 fig. 5) than in Pentacrinus wyviUe-thomsoni (PI. XX. fig. 6). The doulile axial cords 

 of the rays which proceed outwards from it resemble those of Comatulse in their very 

 close approximation. Small portions of them, cut very obliquely, are seen in PI. XXIV. 

 fig. 9, A. They are lodged close together in the same canal as far as the axillary radial, 

 not being so widely separated as in Encrinus ; and the arrangement of the commissures 

 in the axillary is just the same ais was discovered by Ludwig in the Comatulse. 



D. Tlie Geological History of Pentacrinus. 



Excepting for some doubtful forms from the Eifel, the earliest known Pentacrinidaj 

 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 tj'pes occur together in the Wellenkalk of Wiirtemberg ; and he refers all the 

 Pentacrinida3 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 ciiTus- whorls at intervals of eight or ten joints, to the stems of recent Pentacrinidae, 

 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 

 Gruettard and Ellis. Some j^ears later Quenstedt ' gave an excellent figure of it ; but in 

 the absence of an associated calyx lie hesitatedi 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 regai-ded it as a Pentacrinus, as Quenstedt 

 himself has done in the Encriniden, and the reference of the fossil to the Pentacriuidai 

 will now be scarcely disputed. Another very similar stem from the Muschelkalk of 

 Silesia was described by von Meyer* as Chelocrinus acutangidus. 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, 



' Encriniden, p. 198, Tab. 97, iigs. 14-22. 

 - Die Petrefectenliunde, p. .327. 



2 Uebev die Encriniten des Muschelkalks, Archiv f. Katurgesch., Jalirg. i. Bd. ii., 1835, p. 225, Taf. iv. fig. 2. 

 ■* Fische, Crustaceen, Echinodernien und andere Versteinerungen aus dem Musclielkall^ Oberschlesiens, Palajonto- 

 grapliica, Bd. i., 1851, p. 272. 



'^ Ueber Missbildungen von Encrinus liliiformis. Lam., Pala;ontograpliica, Bd. iv., 185G, p. 17G. 



