182 
A zelandiæ the interambulacra are, at the edge of the test, on 
both the oral and the aboral side, about half as w.de as the ambul- 
acra, in A. placenta they are only about V* as wide. But much 
more important is the faet, disclosed by Lov én, that in A. placenta 
the second, third and, partly, the fourth ambulacral plates of the 
adjoining radii meet in the interradial midline, only one pair of 
interambulacral plates being found on the oral side in each inter- 
radius at the edge of test. In A. zelandiæ only the second ambul¬ 
acral plate joins with that of the neighbouring radius, there being 
2-3 pairs of interambulacral plates in each interradius at the edge 
of the test (PI. VI. Figs. 24, 26). In A. placenta there is a naked 
furrow on the oral side in the posterior interradius; this is not 
found in A. zelandiæ. The peristome is distinetly larger in A. ze¬ 
landiæ than in placenta and is pentagonal in the former, nearly 
circular in the latter. The statement of Lovén that in A. placenta 
the apical system is distinetly posterior to the middle of the test, 
while in zelandiæ it is distinetly anterior, seems to me less con- 
stant. Also the differences in the shape of the test and the pos¬ 
ition of the periproct, pointed out by Lov én, appear to be less 
constant. 
According to Lov én there is still another remarkable differ¬ 
ence between the two species, viz. that in Å. placenta the first 
interambulacral plate disappears totally in larger specimens, while 
in zelandiæ it remains large and distinet. In the few specimens of 
A. placenta , which I have been able to examine, this does not hold 
good ■ I find the primary interambulacral plate still quite distinetly 
marked off, even in a specimen of 62 mm length. Upon the whole, 
the shape of buccal rosette differs considerably from that shown 
in Lovén's figures (Comp. PI. VI. Fig. 26 with PI. LI. Fig. 248 
of Lovén; both specimens are of the same size, 45 mm long). 
This faet would seem to indicate that still another species will have 
to be separated from 4. placenta. I have no material for deciding 
this question at present. The specimens at my disposal are 
Cape York, Queensland. 
Regarding the shape and structure of the pedicellariæ (PI. 
Figs. 25, 28) A. zelandiæ does not differ essentially from A. pla¬ 
centa (Comp. H. L. Clark. Hawaiian a. o. Pac. Ech. The Clype- 
astridæ etc. PI. 125. Figs. 1-3). Only one kind of pedicellariæ 
