,0 KCHINOIDEA. II. 



pores being placed in these depressions. The innermost ones are directed almost straight towards the 

 border of the peristome, farther out they become parallel to the ambitus; the same feature is seen in 

 the arrangement of the pores as seen from the outside of the test. (PI. XII. Fig. 27). 



Among the tubercles are seen some mostly rounded, sometimes irregular, glassy protuberances 

 about as large as the primary tubercles; they are only elevations from the test, not carrying spines or 

 pedicellariae. They are specially numerous on the actinal side (PI. XII. Fig. 26), and when seen under 

 the microscope are very conspicuous among the white tubercles on account of their smooth, shining 

 surface. On the abactinal side they are less numerous; such a protuberance is generally situated be- 

 tween the two pores of each pair of the petals, elongated in shape and with a distinct longitudinal 

 furrow in the middle. (PI. XII. Fig. 22.) 



The spines are short, making a dense clothing. The primary ones, about 0-5 c>7 m ' n long, are 

 slightly tapering, densely serrate, except at the base (PI. XII. Fig. 19); those around the peristome are 

 curved. Generally they are a little thicker in the middle, as seen in the figure cited; sometimes they 

 are distinctly widened in the outer part. The point is generally worn off. As pointed out by Agassiz 

 those on the actinal side are somewhat longer than the abactinal ones. The miliary spines (PI. XII. 

 Fig. 9, 18) are only about half the size of the primary ones, a little widened in the point, which forms 

 a sort of crown, the endcrown of de Meijere, to whom belongs the merit of having shown the 

 great systematic importance of the structure of the spines, especially the miliaries, in the Clypeastroi- 

 dea. (Siboga-Echinoidea. p. 113). The longitudinal ribs are slightly widened above with the edge 

 finely serrate, sometimes almost smooth. The small radial plates in the crown are simple or with a 

 few (2, sometimes 3 or 4) dentations. It is worth noticing that, when the living animals are put in 

 alcohol, the spines turn intensely green; this holds good also for sev'eral other Clypeastrids, if not 

 for all of them. 



The pedicellarise are represented by three kinds, viz. ophicephalous, tridentate and triphyllous. 

 The ophicephalous pedicellariae (PI. XII. Figs. 4, 6) are small and rather simple in structure: the blade is 

 narrow, elongated, widening a little in the outer part; the edge is somewhat densely serrate along 

 the whole length. There is no distinct basal part; the articular surface is very strongly developed, 

 the three valves articulating so closely together that it is almost impossible to separate them with- 

 out breaking (in Ech. grandiporus the valves separate easily). In one of the valves the arc is very 

 large; another has the arc prolonged into a long thornlike process, which goes through the hole in 

 the large arc; its point is more or less bent. The third valve has the arc very slightly developed, with 

 no process. (Comp. PI. XII. Figs. 8, 11,12 of Ech. grandiporns). This structure is well seen in the figure 

 given by Cuenot (op. cit. --he wrongly names it a tridactyle pedicellaria) ; de Meijere also gives 

 a description of it (op. cit. p. 108). The head articulates directly with the upper end of the stalk, 

 the large arc resting on the cup-shaped upper end of the stalk, attached by some muscular fibres to 

 the bottom of the cup, as shown in Cuenot's figure. The stalk is comparatively very robust, almost 

 hourglass-shaped, in the middle part it consists of compact calcareous substance, at both ends it is 

 of the common, looser structure. These pedicellariae are especially numerous on the actinal side, 

 behind the anal area. The triphyllous pedicellariae (PI. XII. Fig. 20) are very small, the head not 

 more than ca. o-O4 mm ; the stalk is like that of the ophicephalous pedicellariae, only much more slender 



