A MONOGRAPH OF THE EXISTING CRINOIDS 19 



the subject and with the condition of many recent species of Antedon, as he (Carpenter), 

 had pointed out elsewhere; and the only character, therefore, on which he can possibly 

 rely for the separation of Solanocrinus from Antedon is the presence of syzygies in the 

 arms of the latter and their absence in those of the former genus. But the material 

 on which he has founded this generalization seem.s to be altogether insufficient. Few, 

 if any, of his very limited number of specimens have as many as forty brachials re- 

 maining, and these are rarely in a satisfactory state of preservation, so that it is 

 somewhat rash to speak positively about the total absence of syzygies in the arms of 

 Solanocrinus. Carpenter said that, in fact, he had shown reason to believe that 

 syzygies are present even in some of the arms which are figured and described by 

 Walther as being entirely devoid of them. 



Carpenter remarked that, on the other hand, Antedon andersoni is remarkable 

 for the rarity of the syzygies in the arms. It was a long time before he could discover 

 any at all, except that between brachials 3 + 4. In fact, he did not succeed in finding 

 any in some arms, while in others they are often separated by intervals of ten or a 

 dozen segments. In Antedon elegans {=Zygometra elegans) and A. multiradiata 

 (=Z. microdiscus) the second syzygy may not be until the fortieth or even the sixtieth 

 brachial, and the intervals between its successors may be 15 or 20 joints (that is, 

 16 or 21 muscular articulations). Were these species in the fossil state, therefore, 

 with only the lowest portions of the arms preserved, and that but badly, it would be 

 easy to overlook the syzygy in the tliird brachial (that is, between brachials 3+4) 

 and to infer that none were present in the arms at all, though such an inference would 

 not be in accordance with the facts of the case. Carpenter could not but suspect, 

 therefore, that Walther's attempt to estabUsh the absence of syzygies as a diagnostic 

 character of Solanocrinus was due partly to a generahzation on imperfect material, and 

 partly to an insufficient acquaintance with the variations in the distribution of the 

 syzygies among Recent comatuhds. 



Carpenter said that any member of the Elegans group preserved in the fossil state 

 would made a fairly good Solanocrinus, for each species has a relatively large centro- 

 dorsal bearing a good number of cirri, with few syzygies between the bracliials, but 

 one between the elements of the IBr series. This latter condition certainly occurs in 

 Solanocrinus costatus, and probably also in S. imperialis and S. gracilis, as he has 

 explained elsewhere; and Carpenter was inclined to regard these last mentioned species 

 as the ancestral forms of the existing members of the Elegans group. On the other 

 hand, he said, Antedon scrobiculata and A. aspera, with a bifascial articulation (that is, 

 synarthry) between the elements of the IBr series, were the Jurassic representatives 

 of the majority of the Recent species of Antedon in which the two elements of the IBr 

 series are united by synarthry. 



In 1891 Dr. Clemens Hartlaub described in detail three specimens from the 

 Pelew Islands which he found in the Hamburg Museum labeled Antedon polypus 

 Liitken. One of these was later transferred to the Gottingen Museum. Hartlaub 

 said that a study of the last mentioned specimen showed that the articiJation between 

 the elements of the IBr series is not a syzygy; this articulation not only does not 

 differ externally in any way from the other articulations, but the a.xillary is rather 

 freely movable on the IBri. This species, therefore, can not be assigned to the 

 Elegans group as was done by Carpenter as a result of the erroneous interpretation 



