14 HAWAIIAN AND OTHER PACIFIC ECHINI. 



None of these varying peculiarities of the primary spines are distinctive of 

 particular groups but examination of the miliary spines shows two distinct types 

 of structure, one of which occurs only in two families, the other only in the 

 remaining three. In the Fibulariidae and Laganidae, the miliary spines have the 

 appearance of groups of flattened rods, more or less expanded at their tips, and 

 bound together by horizontal bars placed rather near together. At the base, 

 these spines seem fairly solid but distally they have an open, lattice-like appear- 

 ance. Attention was first called to the characteristic structure of these small 

 spines by de Meijere (1904, loc. cit), who showed how the flattened rods differed 

 in different species. They are sometimes gradually (PI. 124, fig. 14), sometimes 

 abruptly (PL 124, fig. 18) expanded at the tip, and the terminal margin may be 

 smooth or finely or coarsely serrate. The spine as a whole is commonly some- 

 what expanded at tip, i. e. the rods are more or less flaring. Often the rods are 

 not all of equal length but those of one side may be much shorter than the others; 

 in such a case the tip of the spine is more or less oblique. Examination of much 

 material has convinced me that the degree of obliqueness is subject to great 

 variation due to the position of the spine on the test and the amount of wear it 

 has received. The amount of serration on the rod-tips is also affected by the 

 same factors, and smooth, finely serrate, and coarsely serrate rods occur in the 

 same individual. 



In the remaining families of Clypeastrina, the miliary spines are solid like 

 the primaries but the longitudinal ridges are dentate and their chisel-like teeth 

 are more or less finely serrate (PI. 122, figs. 7, 8, 10). Such miliary spines may 

 be cylindrical (PI. 122, fig. 7) or more or less swollen at the tip (figs. 8, 10). 

 They do not show signs of wear as evidently as do the miliaries of the Laganidae. 

 They show little diversity in form or structure and are of little use for systematic 

 purposes. 



One of the most interesting facts brought out by a study of the pedicellariae 

 of the clypeastroids is that these organs reveal a steadily decreasing importance 

 as we pass from the older and more primitive forms to those which are more 

 highly specialized. In most species of Clypeaster pedicellariae of at least three 

 kinds are more or less common, and may even be abundant. No globiferous 

 pedicellariae are known in the genus, or in any of the Clypeastrina, but tri- 

 dentate, ophicephalous, and triphyllous forms occur on both oral and aboral 

 surfaces. As a rule, the ophicephalous pedicellariae are chiefly aboral and the 

 tridentate chiefly oral, while the triphyllous may occur on either surface with 

 equal frequency. In some species, large pedicellariae, like the tridentate, occur 



