62 HAWAIIAN AND OTHER PACIFIC ECHINI. 



The actinostome (PI. 52, fig. 1) is covered with a pavement of three rows 

 of comparatively large pentagonal or hexagonal plates, the row of poriferous 

 plates being the largest. 



The second actinal ambulacral plate in each column and rarely the third, 

 are compound plates (PI. 52, fig. 1). 



The sculpture of the abactinal system consists of an irregular indefinite 

 pattern (PI. 52, fig. 2) which is most prominent on the left lateral genitals 

 and the left anterior ocular. The anal system is wholly included by the 

 suranal plate, the odd and the right posterior genital plates, the right pos- 

 terior ocular not being in contact with the anal system. The genital plates 

 are irregularly longitudinally heptagonal and form a continuous ring. The 

 oculars are pentagonal widest in the angle of contact with the genital 

 plates. The anal system is covered by eight triangular plates, four of which 

 are larger than the others and carry indistinct miliaries. 



Although the primary spines appear to be so characteristic, it is quite pos- 

 sible that more extensive material will prove this species to be based on an 

 aberrant, young individual of miliaris. 



So far as can be determined from the single, small specimen, the pedicel- 

 lariaj do not differ from those of miliaris, but no quadridentate or tridentate 

 pedicellariae were found. 



This species was taken by the " Albatross " only at 



Station 4045. Off Kawaihae Light, W. coast of Hawaii, H. I. Bott. temp. 

 49°. 147-198 fathoms. Co. s. for. One specimen. 



ARBACIADiE Gray. 

 The Pedicellariae and Other Structural Characters. 



Plates 44, figs. 1, 2; 46, figs. 9-16; 47 ; 48 ; 49. 



The pedicellariae of the Arbaciadoe are of two quite distinct tj'pes, the tri- 

 dentate and ophicephalous. Whether true triphyllous podicellariii? also occur 

 is a debatable question, but we have found it convenient to differentiate 

 under that name certain small pedicellariae, occurring in a number of species, 

 in which the valves are relatively wider and more leaf-like than in even the 

 smallest tridentate pcdicellaria3 of the same species. It may be frankly stated, 

 however, that as these small pcdicellaria? intergrade completely, in most cases, 

 with the tridentate and in some species are not distinguishable at all, it would 

 be equally correct to consider them sim})ly as a form of the tridentate, and 



