284 
sometimes only about twice the size of the other marginal plates. 
On seeing the two extremes together one would scarcely think it 
possible that they could belong to one and the same species; but 
all intermediate stages are found, and it is thus beyond doubt that 
we have here to do only with individual variations. On the point 
b. c. d. e. 
Fig. 7. Pentagonaster pulchellus. a. Adambulacral plates; b-e. interradial plates 
with pedicellariæ; in b. the pedicellaria is closed, seen directly from above; 
c. half side \iew, the pedicellaria closed; d. the open pedicellaria in its groove; 
e. an empty pedicellaria-groove; in d. and e. the grains surrounding the plates 
are omitted, a. ; b—e. 
of the arms are found a very small terminal plate and one or 
two pairs of very small plates, evidently representing an outer 
pair of marginal plates. 
The adambulacral plates (Fig. 7.a) carry two thick furrow spines, 
and outside these two other similar but thicker and shorter spines. 
Together with those of the opposite side of the furrow these spines 
form a close covering of the furrow, all the spines standing so 
close together as to be flattened against one another; they do not 
show any distinet serial arrangement. The abradial part of the 
adambulacral plates carry mostly 4 short, grainlike spines, the inner 
two of them triangular, closely appressed to the corresponding ones 
of the adjoining plates. — The mouthplates have an armature 
exaetly like that of the adambulacral plates, 
The interradial areas of the oral side covered with rather 
numerous, not regularly arranged plates, each surrounded by a 
circle of grains as are the plates of the aboral side; but the plates 
are somewhat smaller than the aboral ones, and generally less 
elevated, those in the middle of the area are somewhat larger 
than those along the edges. A various number of the plates along 
the edge or along the ambulacral furrow, sometimes nearly all the 
