ip SK ees ie hai: 
, 
232 THE VOYAGE OF H.M.S. CHALLENGER. 
syzygial joint, but after that the syzygies are not repeated, so that there is only one of 
these peculiar junctions in each arm. . , . And the alternate syzygies in the arms, which 
form so remarkable a character in Rhizocrinus, are absent.” He subsequently stated that 
in Bathyerinus aldrichianus “ the first and second, and the fourth and fifth brachials are 
united by syzygies; and after that the syzygies oceur sparingly and at irregular intervals 
along the arms.”* Jn like manner Danielssen and Koren’ described the first two brachials 
of Bathycrinus carpenteri as united by syzygy; a true articulation between the second 
and third, and also between the third and fourth brachials ; while the fourth and the fifth 
are united by syzygy, the sixth articulated both to the fifth and to the seventh, and the 
ninth both to the eighth and tenth. After this point muscular articulations and syzygies 
alternate all along the arms. Owing to the kindness of Dr. Danielssen I have been able 
to satisfy myself that these “syzygial unions” in the arms of Bathycrinus carpenteri are 
really trifascial articulations like that between the two outer radials of Bathycrinus 
aldrichianus. If, however, this term be substituted for syzygy in the description by 
Danielssen and Koren, their statements respecting the grouping of the brachials would be 
perfectly correct, z.e., in the nine lowest brachials there are alternations of a pair of joints 
united by trifascial articulation and a single joint with muscular articulations at both ends. 
Beyond the ninth brachial the two forms of articulation alternate with great regularity. 
Apart from the question of nomenclature, therefore, the Norwegian naturalists were the 
first who correctly described the grouping of the joints in the arms of Bathycrinus; for 
I find that their description of Bathycrinus carpenter: applies both to the little Bathy- 
erinus gracilis dredged by the “ Porcupine” and to the two Challenger species, Bathy- 
crinus aldrichianus (Pl. VIL figs. 1, 2) and Bathycrinus campbellianus (Pl. VILL. 
figs. 1, 3). The non-syzygial nature of the paired unions in the arms of the two last has 
been determined by actual investigation of the joint faces; while careful microscopic 
examination of the small individual of Bathycrinus gracilis has convinced me that it 
resembles the other three species in this respect. 
The proximal face of the fifth brachial of Bathyerinus aldrichianus is shown in 
Pl. Vila. fig. 19; and that of a later joint in fig. 20. In both cases the three fosse are 
visible around the opening of the central canal; while in Pl. VIIb. fig. 8, the three 
ligamentous bundles uniting the first and second brachials are seen in section (i, ld). 
The same three fosse (/i’, Id’) appear in Pl. VIla. fig. 22, which represents a trifascial 
articular face of Bathycrinus campbellianus; while an ordinary muscular joint-face at the 
proximal end of a brachial is seen in fig. 23, 
The presence of this trifascial articulation, and its peculiar grouping, may therefore be 
considered as distinctive of Bathyerinus. Hence the alternation which was referred to by 
Sir Wyville as so characteristic of Rhizocrinus is repeated in Bathycrinus, though with 
two points of difference. In the latter genus the syzygies of Rhizocrinus are replaced by 
? Journ. Linn. Soc. Lond. (Zool.), 1876, vol. xiii. p. 50. 2 Nyt Mag. f. Naturvidensk., Bd. xxiii. pp. 6,7. 
