92 HAWAIIAN AND OTHER PACIFIC ECHINI. 



The triphyllous pedicellarise are common everywhere on the coronal 

 plates, and are easily recognized by the very slender stalk, several times as 

 long as the head, and the very long neck, about twice the length of the 

 valves. The latter are from .30 to .50 mm. in length and are greatly 

 constricted just above the base. The blade expands at the tip, and is pro- 

 vided with a perforated '•' cover-plate" which conceals more or less of the basal 

 part. Two quite distinct kinds of triphyllous pedicellarioe are found some- 

 times on the same individual. In the common kind the valve (PI. 50, figs. 8, 

 13) is rounded at the tip, and the greatest width of the blade is 1.25 times the 

 width of the base of the valve or less. In the other kind, which seems to 

 be quite rare, the valve (PI. 50, fig. 5) is almost square cut at the tip, and its 

 width there is twice that of the basal part. The larger triphyllous pedicellarite 

 of the common kind intergrade completely with the slender tridentate, the 

 blade becoming elongate and the cover-plate reduced or even practically 

 wanting. Neither tridentate (except form c) nor triphyllous pedicellariae 

 ever have an articular loop. 



The sphoeridia (PI. 50, figs. 2, 10) in the Aspidodiadematidoe are either 

 globular or ovoid and never wider than long. They are suspended by short 

 stalks from minute tubercles on the ambulacral plates, and are entirely 

 on the surface, never sunken in depressions or pits. They are remarkably 

 numerous, for a number are always to be found on the actinal half of each 

 ambulacrum, and not infrequently the abactinal half is also provided with 

 them. In some individuals they extend all the way from peristome to ocular 

 plate, as many as fifteen being found in each ambulacrum. They are rather 

 small, however, seldom exceeding .35 mm. in length. 



The calcareous particles of the pedicels and gills consist of smooth, per- 

 forated plates of comparatively small size and with few holes. In the gills 

 they are quite irregular, but in the pedicels they tend to assume one of two 

 forms : in one the ends are somewhat drawn out, and the perforations are 

 minute and confined to the middle of the plate, while in the other the per- 

 forations are larger and occur in all parts of the usually elongated plates. 

 We are unable to draw any sharp line between these two forms, nor can we 

 find that any generic or specific characters are to be drawn from the cal- 

 careous particles of any sort. 



The arrangement of the internal organs of Aspidodiadema are shown in 

 figures 3 and ^, PI. 44. The reproductive organs are narrow, elongated 

 tufts of rather thick, short tubules, which, when fully developed, occupy 



