18 SALENIA VAEISPIXA. 
existence of a large permanent anal plate in the young of many Echini 
among the Desmosticha. 
I was in hopes that the examination of the series of young Salenite dredged 
by the "Blake" might throw some light on the formation of the suranal 
plate, and its homology with the single large anal plate of the early stages 
of young Echini belonging to other families. On examining these young 
Salenice I find that the abactinal system occupies a comparatively much 
greater space of the abactinal surfiice of the test than in the larger sjieci- 
raens. But in all the young stages, even when not measuring more than 
1.5 mm. in diameter, the arrangement of the plates of the abactinal system 
does not differ from that of the older specimens, the suranal plate being 
only proportionally somewhat smaller. In the youngest Salenia collected 
(1.5 mm. in diameter) the sutures between the genital and ocular plates are, 
as in all yoimg Echini, somewhat indistinct, and it is difficult to define the 
exact limits of the abactinal system. As I have already shown in other 
young Echini (Strongylocentrotus, Echinus, Arbacia, Diadema, etc.), the 
coronal plates of the test and the plates of the abactinal system are very 
indistinct in the stages immediately following the resorption of the Pluteus, 
while the actinal system is well defined. It is only later that the sejiaration 
of the ambulacral and interambulacral areas can be traced ; at about the same 
time the limits of the abactinal system become defined ; and still later, the 
separation of that system into its component plates surrounding the anal 
system, which from the earliest stages is readily recognized. In the young- 
est stage of Salenia the anal system is distinctly pentagonal, and covered 
by eight large triangular plates with rounded tips ; the jslates carry small 
granules supporting minute sessile papillae similar to those found on the 
genital and ocular plates, but smaller. 
As in other young Echini, the anal system is comparatively large ; the 
suranal plate is at first quite small, a narrow plate on the side of the anal 
system opposite to the nearest ocular plate. It appears to gain in size at the 
edges adjoining the genital plates. As fast as the plates of the genital ring 
increase, the pentagon they form round the suranal Y^ate enlarges, and the 
outer edges of this plate keep pace in their growth with that of the inner 
edges of the adjoining genital plates. The genital and ocular plates carry 
three or four large granules irregularly placed on the plates, with a row of 
granules forming a line round the edge of the anal system. There are as 
yet no traces of the genital or ocular openings. The whole of the abactinal 
