GENOCIDARIS APODA. 299 



primordial ambulacrals has a tube-foot and that is the one which according to 

 Lov^n's formula should be the smaller. In Temnotrema Doderleini .(Mortensen) 

 there are but five primordial ambulacral plates, as the original description states. 

 Examination of a specimen shows that, judged by their position with reference 

 to the poriferous areas, these plates are likewise 16, 116, Ilia, IV6, Va. It seems 

 probable therefore that when a tube-foot fails to become associated with one 

 of the primordial ambulacral plates, that plate fails to develop and remains 

 rudimentary as la, Ila, III6, IVa, and V6 are in Genocidaris apoda or e\'en be- 

 comes quite resorbed as the same series does in Temnotrema Doderleini. But 

 why tube-feet fail to become associated with these particular plates still remains 

 to be explained. It may be noted here that in Genocidaris decipiens de Meij. 

 the arrangement of the primordial ambulacral plates accords with Loven's law, 

 for while each plate bears a tube-foot, the two plates of each pair are unequally 

 distant from the mouth, and the distal plate is the larger; the sequence of these 

 distal plates is la, Ila, III6, IVa, V6 as would naturally be expected. 



The primary spines of apoda are remarkably long and slender and so easily 

 broken, that whole ones have been observed only in the smallest specimen. 

 Pedicellariae are not common. Only one globiferous was found; the valves 

 (Plate 93, fig. 16) are about .15 mm. long, the blade is not as tubular as in macula- 

 tus and the end tooth is not particularly long. The ophicephalous pedicellarias 

 have the valves (PI. 93, fig. 17) about .20 mm. in length and distinctly con- 

 stricted at base of blade. No trideniate or triphyllous were found, nor were 

 either sphaeridia or calcareous spicules noted. 



The test and spines are white with a grayish tinge and in the small specimen 

 the terminal half of the longer primaries is red. 



This little sea-urchin differs so decidedly from the other species of Genoci- 

 daris that it cannot fail to be recognized. The plates of the abactinal system 

 are so much larger, thinner, and smoother than in decipiens or rnaculata that even 

 aside from the peculiarly characteristic buccal plates, it would be easily dis- 

 tinguished. 



It was taken by the ''Albatross" at only two stations: — 



Station 4891. Southwest of Goto Islands, Japan; 32° 27' N., 128° 34' E. 

 Bott. temp. 50.2°. 181 fathoms. Gy. s., brk. sh., r. 



Station 4904. Southwest of Goto Islands, Japan; 32° 31' 20" N., 128° 32' 40" 

 E. Bott. temp.? 107 fathoms. Fne. gy. s., brk. sh. 



Three specimens. 



