90 HAWAIIAN AND OTHER PACIFIC ECHINI. 



will not be out of place. There are no constant differences between the 

 pedicellariae of Dermatodiadema and those of Aspidodiadema, but there are 

 such differences between the larger pedicellaria3 of some of the species 

 of Dermatodiadema which are useful in their identification. 



The size and form of the pedicellariiB show an extraordinary diversity, 

 as many as seven different kinds sometimes occurring on a single specimen, 

 wliile most individuals have at least four. There can generally be found 

 triphyllous, oplucephalous, and tridentate pedicellarite ; in some individuals, 

 two forms of triphyllous occur, while there are very commonly two forms 

 of tridentate present, and there may be three or four. The stalks of the 

 pedicellariae are calcareous rods, more or less enlarged, and fenestrated at 

 the ends, the extent of the fenestration depending chiefly on the size of the 

 pedicellaria. 



The tridentate pedicellarias in their most common form have the valves 

 long and slender (PI. 50, figs. 7, 1£), usually straight, but sometimes curved ; 

 these may be called the " slender irideniafe." Other very large pedicellaria? 

 are usually present of which the three valves are very bi'oad and deep in 

 proportion to their length and have the blade more or less filled by a 

 calcareous network (PI. 50, figs. 1, 6, 11). These pedicellariae are called 

 " globifere " by Doderlein, which is convenient but inaccurate, as they are 

 certainly not homologous with the globiferous pedicellarise of the other 

 Diadematoida. Mortensen calls them "large ophicephalous," and while in 

 some cases their resemblance to ophicephalous pedicellarite is apparent, the 

 absence of an "articular loop" and their great size are objections to regard- 

 ing them as such. As de Meijere calls them " grosse tridentate," and we 

 incline to the view that that name best expresses their real character, we 

 shall desio-nate them as " stout tridentate. " K\i\\owA\ these stout triden- 



o o 



tate pedicellaria? usually have the blade rather deep, with the sides converg- 

 ing to a blunt point, they sometimes occur with broad, rather flat blades 

 and wide tips (PI. 50, fig. 3) ; such pedicellariae may be designated as " form Z*." 

 Another peculiar form is rarely found, which is quite intermediate be- 

 tween the tridentate and ophicephalous pedicellariaj, having the "articu- 

 lar loop " of the latter and the blade free from a calcareous network, but 

 with the general appearance of the former (PI. 50, fig. i) ; these may be 

 called " form c." 



The slender tridentate pedicellariae are very common, and occur on all parts 

 of the test, even on the abactinal system and the buccal membrane. The 



