ME. P. H. CAEPEXTEE OX THE GEXTJS ACTIXOATETEA. 45 



series 96 were normal, and that out of 70 palmar series 65 were normal, i. e. consisted 

 of three segments, of which the second bore a long pinnule, while the third was axillary, 

 with a syzygiiun. The three forms of variation exhibited by the abnormal palmar 

 series are of considerable interest, because some of them, at least, represent the normal 

 condition of the palmars in other groups of Actinometrce. Thus the most frequent one, 

 two palmars on three distichals, is typical for Act. multifida, while that of three palmars 

 on two distichals is typical for Act. rotalaria. The third variation, two palmars on two 

 distichals, occurs in Act. tenax, Ltk , and in a few new ' Challenger ' species ; and it is 

 typical in several species of Antedon — for example, in. Ant. palmata and Ant. articulata. 

 Specimens Xos. II. and III. are remarkable for the fact that the numbers of regular and 

 irregular distichal series are in each case equal to one another; so that a specific diagnosis 

 based upon either of these specimens alone, would, as is evident from the above Table, 

 have been entirely incorrect. 



The amount of variation in these characters is so enormously great that only after 

 examination of a considerable number of specimens is it possible to draw conclusions 

 of any value respecting the use which may be made of these characters for systematic 

 purposes. The above Table, however, will, I think, show clearly that I am justified 

 in assuming the normal number of both distichal and palmar segments in this species 

 to be three, of which the second bears a long pinnule, and the third is axillary with a 

 syzygium. 



(§31) The same variability occurs in the position and distribution of the syzygia 

 in the arms, but, as might be expected from the nature of the case, to an infinitely 

 greater extent. In most of his specific diagnoses Miiller gives the position of the first 

 svzv^iuin on the arm and the average number of segments which occur between everv 

 two successive syzygia throughout the rest of the arm. Only in a very few cases 

 does he make mention of the position of the second syzygium, which I believe to be 

 a character of nearly or quite as great systematic value as the position of the first ; and, 

 owing to its greater constancy, of considerably greater value than the number of seg- 

 ments between every two successive syzygia, which I will call the " syzygial interval." 

 It will be seen from Table I. that the total number of arms in the 12 specimens of 

 Act. polymorpha at my disposal reached 310 : 11 of these were broken below the third 

 segment ; but of the remaining 299, the first syzygium was on the third brachial in 

 283 cases ; and in 156 of these the second svzv«ium was on the tenth brachial. The 

 irregnlarities in the position of the first syzygium were limited to tbree specimens, 

 and, as will be seen from Table II., nearly all confined to one variety. 



