DIADEMATID^. 105 



an articular loop, which differs greatly in size in the three, and may be 

 wholly wanting in one. The blade may be sinuate, coarsely dentate, serrate, 

 or nearly smooth on the margin. 



The glandular ophicephalous pedicellariaB (PI, 51, fig. 6) do not differ in any 

 essential particular from the non-glandular save in the presence of three 

 conspicuous glands on the stalk. It is quite possible that this diflference is 

 due to the stage of development of the pedicellaria, or even that it is 

 apparent rather than real, the diflference in appearance being due to the 

 condition of the glands. 



The claviform ophicephalous pedicellarife appear to be simply a degrada- 

 tional form of the glandular ophicephalous, in which the glands seem to be 

 developed at the expense of the valves, the latter becoming very small or 

 more often entirely wanting. Such pedicellariae are very common in the 

 DiadematidjB, especially on the actinal side of the test. 



The triphyUous pedicellarife (PI. 51, figs. 7, 15) are generally common, 

 scattered all over the test, but \i\ some cases are rather rare. The heads 

 are small, only .20-.40 mm. long, and are attached to the very slender stalk 

 by a long neck. The valves (PI. 50, fig. 18) are flat and more or less leaf- 

 shaped, sometimes narrowed and rounded at the tip, but more commonly 

 truncate or square-cut, and in some cases widest there. No cover-plate is 

 present; Mortensen (1904) describes and figures a cover-plate on the valve 

 of the triphyllous pedicellariae in Micropyga, but there is none in the speci- 

 mens we have examined, and if it occurs, it must be quite unusual, and not 

 the normal condition. 



The globiferous pedicellariae (PI. 51, figs. 8, 16) are very diflferent from any of 

 the preceding, and are characteristic of the genus Centrostephanus. They 

 are conspicuous because of the glands, which not only enclose and may 

 even entirely conceal the valves, but which may also occur on the upper part 

 of the stalk. There is no neck, but the stalk is 2-8 times as long as the 

 head. The valves (PI. 51, figs. 9, 10, 18, 19) are small, rarely exceeding 

 .45 mm. in length. The basal part is wide, but the blade is abruptly nar- 

 rowed and at the tip is provided with 4-6 very long and conspicuous teeth. 

 The blade may be shorter than the basal part, and quite evidently hollowed 

 or concave on the inner side, or it may exceed the basal part and be nearly 

 cylindrical, hardly more than flattened on its inner face. The glands vary 

 greatly in their development in different examples. They are sometimes 

 scarcely evident on the stalk but very conspicuous on the valves (PI. 51, 



