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



syzygial joint, but after that tlie 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 Bathycrinus aldrichianus " the first and second, and the fourth and fifth brachials are 

 united by sj'zygies ; and after that the syzygies occur sparingly and at irregular intervals 

 alons the arms."^ In like manner Danielssen and Koren'^ described the first two brachials 

 of Bathycrinus carjpenteri 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 " syzj^gial 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 descrijation by 

 Danielssen and Koren, their statements respecting the grouping of the brachials would be 

 perfectly correct, i.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 naturahsts were the 

 first who correctly described the grouping of the joints in the arms of Bathycrinus ; for 

 I find that their description of Bathycrinus carpenteri applies both to the little Bathy- 

 crinus gracilis dredged by the " Porcupine " and to the two Challenger species, Bathy- 

 crinus aldrichianus (PL VII. figs. 1, 2) and Bathycrinus campbelUanus (PL VIII. 

 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 ^ther three species in this respect. 



The proximal face of the fifth brachial of Bathycrinus aldrichianus is shown in 

 PL Vila. fig. 19 ; and that of a later joint in fig. 20. In both cases the three fossae are 

 visible around the opening of the central canal ; while in PL Vllb. fig. 8, the three 

 ligamentous bundles uniting the first and second brachials are seen in section (//, /(/). 

 The same three fossae {li', Id') appear in PL Vila. fig. 22, which represents a trifascial 

 articular face of Bathycrinus camphellianus; 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 Bathycrinus. Hence the alternation which was referred to by 

 Sir Wyville as so characteristic of Rhizocrinus is repeated in Bathycrinus, though w^th 

 two points of difference. In the latter genus the syzygies of Rhizocrinus are replaced by 



^ Journ. Linn. Soc. Land. (Zool.), 1876, vol. xiii. p. 50. ' jVj/i Mag.f. Natiirvidensk., Bd. xxiii. pp. 6, 7. , 



