Oeneric Position o/"Solaiiocrinus. 87 



the case in Walther's Solanocrinus imperialis and also iti 

 S. gracilis. The five single axillaries in the former tjpe, 

 which he describes, may really be double or syzygial joints ; 

 while the two elements of the syzygy are more distinctly 

 separated in the other five primary arms. Without seeing 

 the specimen, however, I should not like to speak positively 

 upon this point, though my experience with several recent 

 Comatula3 leads me to think it by no means an improbable 

 supposition. 



But whether Solanocrinus imperialis have two radials 

 only^ as described by Walther, or three witii the two outer 

 ones united by syzygy, as seems to me not unlikely, I am 

 pretty sure that the arms were not so entirely devoid of syzy- 

 gies as they are said to be by Walther. Thus, for example, 

 in Zittel's figure of the specimen * there is an unmistakable 

 syzygy represented in the third arm from the bottom on the 

 right side. The first thirteen brachials above the distichal 

 axillary are very regular, and, the lowest ones excepted, 

 they show a distinct alternation of long and short sides ; but 

 the thirteenth joint is followed by two others (fourteenth and 

 fifteenth), both of which are longest on the opposite side of 

 the arm to its own longer side, and the long side of the joint 

 which succeeds them (sixteenth) is on the same side of the 

 arm as this is. To my mind this proves clearly that the 

 fourteenth and fifteenth brachials are united by syzygy^, 

 exactly as in the arm of S. costatus, which 1 have already 

 discussed. It is singular, however, that there is no trace of 

 this arrangement in the corresponding arm in either of 

 Walther's figures of this unique speicmen. It is No. 13 of 

 his nomenclature ; but the condition of arm No. 2, as shown in 

 both his figures, seems to me to point unmistakably to the 

 presence of a syzygy. The twenty-first joint, which is at the 

 widest part of the arm, is unusually short, its distal edge being 

 transverse, and not oblique to the axis of the arm, as those 

 of the joints immediately preceding are. In fact, the normal 

 arm ends here, and a small curved stump projects from the 

 middle of the distal face of the short twenty-first joint ; but 

 its diameter is very much less than that of the normal arm. 

 This sudden constriction of the diameter of the arm appears 

 to me to be due to the fact that it had been regenerated, and 

 that the unusually short twenty-first joint is the hypozygal of 

 the syzygy at which the distal part of the arm broke off. 

 Walther's own experiments at Naples showed him that rege- 

 neration takes place twice as frequently from a syzygy as from 

 an articulation ; and the fact that the plane of regeneration is 

 in this case transverse, and not oblique to the axis of the arm, 

 * Palaeontologie, p. 396. 



