288 HAWAIIAN AND OTHER PACIFIC ECHINI. 



and several miliary tubercles. Oculars I and II are broadly in contact with the 

 periproct but the other three are completely excluded. The periproct is very 

 large and of peculiar shape. The end opposite the anal opening is covered by a 

 suranal plate which is larger than an ocular, and resembles that of many Saleni- 

 idse in being in contact with four genitals; but the arrangement is unlike any 

 known in that family in that it is genital 1 which does not touch the suranal. 

 The suranal bears a tubercle similar to those on the genitals. The remainder 

 of the periproct is covered by ten or a dozen plates of which the largest adjoin 

 the suranal. The poriferous areas are broad (each about equals half the inter- 

 poriferous area) for the pores are rather large and the arcs are quite oblique. 

 Near the peristome the areas become narrower as the arcs become more vertical. 

 The actinostomal membrane (PL 102, fig. 2) is thin and perfectly naked, save 

 for the very small buccal plates. The gill-cuts are deep and sharply defined. 

 The auricles meet across the ambulacra forming a closed arch. The spines are 

 fairly long, moderately stout, and rather blunt, the primaries extending far 

 beyond the secondaries. 



The pedicellarise resemble those of G. Robillardi. The globiferous are common 

 and variable in size and proportions. The valves range from .35-.50 mm. in 

 length, of which from one third to one half is the tubular blade. The ophicepha- 

 lous are very common and show little diversity, except in the amount of 

 constriction at the base of the blade. This may be distinct or scarcely noticeable. 

 The valves are about .25 mm. in length, besides the loop which adds .05-.08 

 more. No tridentate pedicellarise were found. The triphyllous are not very 

 common nor variable; the valves are about .10 mm. long. No spicules or 

 sphseridia were noted. 



The specimen is perfectly white save for the tube-feet and buccal membrane 

 which are light brown ; on neither test nor spines is there a trace of color. 



This specimen was dredged in the Persian Gulf in 1894 or 1895 by Capt. 

 F. W. Townsend, but there are no data to show either the exact locality or the 

 depth. If the remarkable suranal plate proves to be a constant character, it 

 will serve to distinguish this species at once from all other known Echini. If 

 however it is a variable feature, carried to an extreme in this particular indi- 

 vidual, then the coloration and the deep gill-cuts become more important specific 

 characters. Should the gill-cuts also prove to be a variable feature, megaloplax 

 might be regarded as a synonym of Robillardi as it would be impracticable to 

 distinguish between them. 



