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54
Randplade, imedens den undre, lidt konvexe Flade,
bidrager i Forening med Yentralpladen til at danne et fælles
Støttepunkt for den brede, paatversgaaende Paxillarrække,
der er nærmest Furepapillerne.
De ventrale Randplader, Tab. IX, Fig. 13, b, ere
ligeledes fladtrykte; de ere noget bredere end de dorsale,
men have ligesom disse en trekantet Form, hvis bredere
Del vender udad og danner med sin undre Flade
Støttepunktet for den dorsale Randplade. Den ventrale
Randplades smalere Del vender indad; dens øvre Flade er
konkav og hviler for største Delen paa Adambulacralpladens
undre, afrundede Rand, Tab. IX, Fig. 13, a (i
Interbrachi-alrummet støder den til en Bugplade); dens undre Flade
er lidt konvex og danner i Forening med den dorsale
Randplades bredere Del en Slags Articulationsflade for
den føromtalte, paatversgaaende Paxillarrække.
Saavel de dorsale som ventrale Randplader staa paa
Armens bredere Del og i Armvinkelen lidt fra hverandre,
men staa tættere og tættere sammen, alt eftersom de nærme
sig Armenden.
Solaster papposus har ogsaa to Rækker Randplader,
der ligeledes ere vel skjulte, men adskille sig dog fra dem
hos endeca væsentlig derved, at de hos papposus tilsammen
bære kun en Række Paxiller, imedens de hos endeca bære
hver sin, altsaa to.
De dorsale Randplader hos Sol. papposus ere
temmelig smaa, Tab. IX, Fig. 12, c, og ere paa den øverste
Del af Armen aflange, imedens de midt paa og paa den
smalere Del ere næsten terningformede. Der, hvor de
bære en Paxille, støde to sammen, Tab. IX, Fig. 12, c,
og danne paa deres ydre Ende en konkav
Artikulations-flade, der optager den store Paxille, som danner Grændsen
imellem Ryg og Bug; meget ofte støde dog en
Kalktrabe-kels indre Ende til den nævnte Ledflade for ligesom at
fuldkommengjøre denne, Tab. IX, Fig. 12, d, for
Paxil-lens store Ledhoved. Imellem disse dorsale Randplader,
der danne Artikulationsfladerne for Paxillerækken, er der
andre dorsale Randplader, der ingen Paxiller bære, men
kun med sin ydre Ende forene sig med det almindelige
Kalknet. De dorsale Randplader hvile med sin indre Ende
paa de ventrale Randplader, — stundom støtte to af de
førstnævnte sig til en ventral Randplade.
Paa ældre Dyr ere de dorsale Randplader, der danne
den førbeskrevne Ledflade, fuldstændig sammenvoxet med
Paxillens Basaldel, og da artikulerer denne med den
tilsvarende ventrale Randplade, — fjerner man saa en af
disse Paxiller, ser det ud, som • om der ingen dorsale
superior, slightly concave, surface, upon the corresponding
ventro-marginal plate, whilst, the inferior, slightly convex
surface, in conjunction with the ventral plate, assists, in
forming a joint support for the broad transverse paxillar
series found next to the furrow-papillæ.
The ventro-marginal plates (Pl. IX, fig. 13, b) are
also flattened, but they are somewhat broader than the
dorsal plates, yet, like these have a triangular shape, with
the broad part turning outwards and forming with its
inferior surface, an abutment for the dorso-marginal plates.
The-accuminate part of the ventro-marginal plates turns inwards,
and the superior surface is concave; the greater portion
of it, rests on the inferior rounded margin of the
adambulacral plates (Pl. IX, fig. 13, a), (it unites, in the
interbrachial space to a ventral plate). The inferior surface
is slightly convex, and in conjunction with the broad part
of the dorso-marginal plates, forms a kind of articulator}’
surface for the transverse paxillar series previously
referred to.
Upon the broad pai*t of the rays, .and also, in the
brachial angle, both the dorso-marginal and the
ventro-marginal plates, are situated a little apart, but they come
together, gradually, closer and closer, as they arrive at the
tip of the ray.
Solaster papposus has also two series of marginal
plates, which are, likewise, well concealed, but yet, differ
from those of endeca, principally, in this, that in Solaster
papposus, they carry, jointly, only one series of paxillæ,
whilst, in Solaster endeca, they each carry one series,
together two series of paxillæ.
The dorso-marginal ’plates in Solaster papposus are
rather small (Pl. IX, fig. 12, c), and upon the superior
portion of the ray, they are oblong, whilst, upon the mesial
part, and on the narrow part of the ray, they are nearly
dice-formed. At the point where they carry a paxilla,
two of them unite (Pl. IX, fig. 12, c), forming on their
exterior extremity a concave articulatory surface, which
receives the large paxilla which forms the margin between
the abactinal and actinal surfaces: very frequently however,
the inner extremity of a calcareous trabeculum abuts upon
the articulatory surface referred to, completing it, as it
were, (Pl. IX, fig. 12, d) to reccive the large articulating
head of the paxilla. Between these dorso-mai-ginal plates
forming the articulatory surfaces for the paxillar series,
there are other dorso-marginal plates which carry no
paxillæ, but connect to the general calcareous reticulation with
their outer extremities only. The dorso-marginal plates
rest, with their inner extremities upon the ventro-marginal
plates, and occasionally, two of the first named plates, join
themselves to one ventro-marginal plate.
In aged specimens, the dorso-marginal plates forming
the previously described articulatory surfaces, are completely
grown together at the basal part of the paxillæ, and in
this case, the paxillæ articulate wiih the corresponding
ventro-marginal plate. When we remove one of these
paxillæ it appears as if no dorso-marginal plates were to be
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