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



which he provisionally named Hyocrinus hethellianus? with the following remarks : — 

 " The last is a beautiful little thing which we dredged from a depth of 2325 fathoms at 

 Station 223, in lat. 5' 31' N., long. 145° 13' E., in the east Pacific, with a bottom of 

 Globigerina ooze, and a bottom-temperature of 1°*2 C. It certainly is in many respects 

 very unlike the adult Hyocrinus hethellianus; but it may possibly turn out to be the 

 young of that species. There was only one specimen." ^ No reference whatever was 

 made to this type in the description of Hyocrinus which was subsequently published in 

 The Atlantic, and is substantially the same as that which appeared in the Journal of the 

 Linnean Society. One would be inclined to conclude from this that the specimen in 

 question was not a young Hyocrinus after all ; for even though it was obtained in the 

 Pacific, reference would probably have been made to it in Sir W}"^'ille's later account of 

 this very interesting genus. But as the specimen has totally disaj^peared, and has eluded 

 all Mr. Murray's anxious search, I am naturally unable to say anything about it. 



B. On the Systematic Position of Hyocrinus. 



Hyocrinus was established by Sir W3^viUe Thomson in the year 1876,^ with the 

 remark that " it presents certain general resemblances and even certain correspondences 

 in structure which seem to associate it also with Rhizocrinus. There seems little doubt 

 that Rhizocrinus finds its nearest known ally in the Chalk and Tertiary Bouryueticrinus, 

 and that it must be referred to the neighbourhood of the Apiocrinidse. Were it not that 

 Bathycrinus and Hyocrinus are so evidently related to Rhizocrinus, the characters of the 

 Apiocrinidse are so obscure in the two first-named genera that one would certainly have 

 scarcely been inclined to associate them with that group." Bathycrinus, though an 

 aberrant form, is far more closely related to Rhizocrinus than Hyocrinus is. It has the 

 same form of stem-joint and the same absence of pinnules from the arm-bases ; while the 

 arm-joints themselves are united in pairs in a very nearly similar manner in both genera. 

 But except in this last point, there is no resemblance between Rhizocrinus and Hyocrinus. 

 The only knouTi species of the latter genus was said by Sir WyviUe Thomson to have 

 " much the appearance, and in some prominent particulars it seems to have very much 

 the structure, of the Palseozoic genus Platycnnus, or its subgenus Dichocrinus."^ In 

 fact, Sir Wjrville seems to have had considerable hesitation in referring Hyocrinus to the 

 Apiocrinidse ; and it was eventually associated by Zittel along with PlicaAocrinus, in a 

 family Plicatocrinidse. But the definition which he gave of the family was far from being 

 a satisfactory one, as it stated that basals were absent, which is by no means the case in 

 Hyocrinus, and also that there are long, forked arms. Since then, however, he has found ■ 

 that there is an axillary second radial (first brachial, Zittel) in PlicaAocrimis, which thus 



1 Journ. Linn. Soc. Land. (Zool.), vol. xiii. p. 55. ^ Ihid., p. 48. ^ Ihid., p. 51. 



