ECHINONEUS CYCLOSTOMUS. 49 
THe ABACTINAL SYSTEM. 
Plate 14. 
At first it was intended to limit this report to a few plates, and a more 
careful examination of the abactinal system was left for the future. 
In a young specimen from Makemo, 4.40 mm. in length, interior view (PI. 
14, fig. 2), none of the genital plates have received their pore, excepting a few 
madreporic perforations on the madreporite. Of the two posterior genital plates 
the one towards the right posterior interambulacrum is slightly larger than its 
mate; both are about as high as broad and in contact with the ocular plates in 
the bivium; of the two anterior ones the madreporic is the larger. Seen from 
the exterior (fig. 7), the apex is slightly raised, carries a few miliaries and a 
small number of the glassy tubercles. 
Another specimen 4.19 mm. in length, from Port Antonio (Pl. 14, fig. 3), 
differs from the previous one only in the left anterior genital being slender, and 
the right posterior genital having pushed itself between the ocular plates of the 
bivium, which in fig. 2 are in apposition. 
Of two specimens, one 12.5 mm. long from Port Antonio (Pl. 14, fig. 4), 
the other 27 mm. in length (PI. 14, fig. 7) from Makemo, the genital plates corre- 
spond exactly to each other in form and size; the anterior plate being longer 
than the posterior which is the reverse of what is shown in figs. 2 and 3; here the 
two large plates are posterior, with the larger one in the right posterior inter- 
ambulacrum, while in figs. 4 and 5 these are in the left posterior interambula- 
crum. The system of the four genital plates are arranged in a square and are 
in contact; their form and that of the pentagonal shaped ocular plates are very 
similar to the figure of Hemiaster expergitus in Lovén’s Etudes (PI. 11, fig. 93), 
and of Periaster tenuis in Agassiz’s Panamic deep sea Echini (p. 210). In two 
specimens (PI. 14, figs. 5, 6), from the Pacific, measuring 26, 27 mm. in length, 
one (fig. 5) has very small genital pores, about one third the size of the other 
(fig. 6); this may be due to sex; the glassy tubercles are larger, darker, and 
more numerous in fig. 5 than in fig. 6. This variation is found in alcoholic as 
well as in dry specimens. 
