EEPOET ON THE CRINOIDEA. 205 



axillaries, like those visible iu the next youngest specimen (PI. IV.) ; whereas the hexa- 

 gonal plates themselves are separated in this manner. 



Further, in nearly all Neocrinoids which have ten or more arms there are three 

 radials. This is true of all the recent Crinoids except Metacrinus, which has a larger 

 number, four or six ; and the only fossil genus which has two radials is the aberrant 

 form Plicatocrinus. 



In all the Neocrinoids, except de Loriol's recently established genus Eudesicrinus, 

 there is either a syzygy or a ligamentous articulation between the two outer radials ; and 

 the existence of a syzygy in Holopus is therefore nothing unusual, though there is less 

 evidence of its presence in the adult condition than is usually the case. But this is 

 scarcely surprising when we remember the excessively intimate union of the first radials, 

 of which no indication whatever is visible on the exterior of the calyx. Some individuals, 

 however, exhibit distinct traces of a sutural line dividing the large axillary into two parts. 

 Such a line is visible in the young specimen (PI. IV.) on all the axillaries of the trivium, 

 crossing them at the point where the medio-dorsal ridge bifurcates as described above ;^ 

 but it is less distinct in the two bivial axillaries. On the other hand, the three trivial 

 axillaries of the large American specimen present no indications whatever of being 

 composite joints, and have a regular, broadly pentagonal shape. This is well shown in 

 PI. I. fig. 2 ; but the bivial axillaries represented in fig. 1 are of an entirely different 

 character, each of them being distinctly in two parts, which look as if they were 

 articulated rather than suturally united, while they do not present the symmetrical 

 appearance characteristic of the corresponding parts in other Crinoids. 



In the one case there is a large and wedge-shaped second radial which has all the 

 appearance of an ordinary brachial. It supports a triangular axillary, but the apposed 

 faces of the two do not correspond exactly. The axillary extends beyond the narrower 

 end of the second radial, and so comes in contact with the upward extension of the first 

 radial akeady described. This is shown in PI. I. fig. 1. The broader end of the second 

 radial, however, extends considerably beyond the axillary, and meets not only the com- 

 posite axillary of the adjacent trivial ray, but also the first brachial of its own ray as well 

 as that of the next. 



The second radial of the other bivial ray, which is shown in the middle of PI. I. fig. 1, 

 is more oblong than its fellow. Like it, however, it is wider than the roughly triangular 

 axillary, and supports a considerable portion of the large first brachial. But it is not 

 overlapped by the axillary at the other end, and completely cuts it ofi" from the first 

 radial below. 



None of the four remaining axillaries of the specimen figured in PI. II. show any 

 distinct traces of their being of a composite character ;'" though there are some lines upon 



* These lines are not clearly seen in tlie positions of tlie specimen which are represented on PI. IV. 

 2 The lower angle of one of these exhibits an accidental fracture. 



