REPORT ON THE CRINOIDEA. 93 



Actinometra, both ten-armed and multibrackiate, e.g., Actinometra pectinata, Actinometra 

 paucicirra and Actinometra typica (PL LIII. fig. 15; PL LIV. figs. 1, 2; PL LVII. 

 fig. 1). 



I do not know, however, of any ten-armed Antedon belonging to this group, and the 

 three species immediately to be described, in which the rays divide three or four times, 

 present one very exceptional feature in their organisation. It is a very general rule 

 among Neocrinoids that the mode of union of the first and second joints beyond the 

 radial and all subsequent axillaries is the same as that between the two outer radials. 1 

 But this rule does not always hold good in the case of syzygial unions, though it is true 

 amongst other species, of Pentaerinus wyville-thomsoni and Pentacrinus alternicirrus, 

 of Actinometra difficilis and Actinometra paucicirra (PL L1I. fig. 2 ; PL LIV. 

 figs. 1, 2), in all of which the two outer radials, the two distichals and the first two 

 brachials are respectively united by syzygy. 



In Actinometra multibrachiata and in Actinometra typica there are three joints in 

 the distichal series, the first two articulated and the third a syzygy. But in the numerous 

 remaining arm-divisions there are only two joints which are united by syzygy like the 

 two outer radials (PL LVI. fig. 2 ; PL LVII. fig. 1). 



The three species of Antedon now to be described are, however, still more irregular ; 

 for in neither distichal, palmar, nor brachial series are the first two joints united by 

 syzygy, as is the case with the two outer radials. This latter character seems to have 

 presented itself in three Jurassic species of Antedon. Quenstedt 2 has described the two 

 outer radials of Solanocrinus (Antedon) costatus as united by syzygy, and his description 

 is borne out by his figures, one of which shows a first brachial of such a size that I feel 

 tolerably certain of its being really a syzygial joint as in Actinometra strata and Actino- 

 metra pectinata (PL LIII. figs. 2, 15). Walther's recent description of Solanocrinus 

 costatus 9 contains the passage "Radiale II. mit Radiale IIT. versckmolzen, doch durch 

 eine Nahtlinie getrennt ;" and it is odd that he did not follow Quenstedt in describing 

 the union as a syzygial one. The large size and the pentagonal shape of the radial 

 axillaries in his Solanocrinus imperialis seem to me to indicate clearly that these are 

 syzygial joints ; and I am very strongly inclined to believe that the large joints which 

 he describes as " Axillaria" are really compound joints, consisting of the first and second 

 distichals united by syzygy, as in Actinometra paucicirra (PL LIV. figs. 1,2). These 

 pieces are more distinctly separate in the five remaining distichal series of his specimen, 

 while in some cases at any rate, the large first brachials would appear to be syzygial 

 joints. The same may be said of Walther's single specimen of Solanocrinus gracilis, 4 of 

 which he remarks as a possibility that the apparently simple second or axillary radial 

 " als verschmolzenes Radiale II. + Radiale III. aufgefasst werden konnte." 



» See Part I. p. 49. 2 Encriniden, p. 17:2, Tab. 96, figs. 26, 28. 



3 Op. cit., p. 172. 4 Ibid., p. 174. 



