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



life, is valueless. For individuals of Pentacrinus decorus have been found attached to 

 teleoraph cables by a spreading base ; and one specimen of Pentacrinus asterius at any 

 rate, which I have seen, had the stem broken at a nodal joint, which was worn and rounded 

 below, its central canal being closed up by a small median tubercle ; while this condition 

 is common to several other Pentaerinidae, as I have pointed out already {ante, pp. 18-22). 



Apart from the length of the internodes and the characters of the stem-joints, cirri, 

 and arms, all of which are merely of specific value, the chief difference between 

 Pentacrinus asterius and Pentacrinus decorus is in the mode of union of the two outer 

 radials. In the latter type, as shown in PL XXXIV. figs. 3 and 5 (wdiich were drawn 

 under Sir Wyville's own direction), these joints are united by a bifascial articu- 

 lation. But in Pentacrinus asterius (PL XII. figs. 18 and 21), and also in Pentacrinus 

 miilleri and Pentacrinus wyville-thomsoni (PL XVIII. figs. 8, 11), there is a syzygy in 

 this position. This difi"erence, however, is one which occurs continually among the 

 numerous species of the Comatulid genera. Antedon rosacea and Actinometra meridion- 

 alis are types of many species having the bifascial articulation ; while Antedon Jluctuans^ 

 and Actinometra Solaris represent a smaller number of species which have the syzygy. I 

 see no reason, therefore, for considering this difi'erence as one of subgeneric value among 

 the Pentacrinidge, so as to separate Pentacrinus decorus, together with Pentacrinus hlakei 

 and Pentacrinus naresianus under a separate name, Neocrinus, from the other five species 

 which have a syzygy between the two outer radials. Four of these, and probably 

 Pentacrinus asterius as well, become free at a certain period of their life, just as Sir 

 Wyville discovered to be the case in Penta.cHnus decorus; so that one of the physiological 

 characters on which he relied as giving Neocrinus an intermediate position between Penta- 

 crinus asterius and the Comatulse is of much more general occurrence than he supposed. 



The separation of Pentacrinus asterius and Pentacnnus decorus as types of sub- 

 genera appears to have been abandoned by Sir Wyville within a year after he had proposed 

 the name Cenocrinus for the former species. For in his well known memoir On the 

 Embryogeny oi Antedon rosaceus, published in the Philosophical Transactions for 1865, 

 frequent reference is made to Pentacrinus (Neocrinus) asterias as well as to Pentacrinus 

 {Neocrinus) decorus ; while Oersted's species Pentacrinus miilleri was also referred to the 

 subgenus Neocrinus. Sir Wyville seems, therefore, still to have regarded Pentacrinus 

 hriareus as having the first claim to the generic name Pentacrinus, although the Messrs. 

 Austin had expressed an opposite opinion. He appears, however, to have eventually 

 adopted their view, as all later writers have done. For in The Depths of the Sea 

 reference is made to two AVest Indian species only, viz., Pentacrinus asterius and Penta- 

 crinus miilleri ; ^ and neither Neocrinus nor Cenocrinus is mentioned, while Pentacrinus 

 decorus is confused with Pentacrinus miilleri. Subsequently also, when describing new 



1 The specific formula of this type is— A.R. 3.2.2.^. 



2 The Depths of the Sea, pp. 436, 442, 1873. 



