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90
3 staa paa hver Sidekant og 1 paa Hjornet af Vinkelen
ind til Furen. Fig. 4, a. 5, a.
De 3 Sidepigge (undertiden findes dog 4 paa den ene
Side) ere fladtrykte; deres frie Ende er temmelig skarp og
takket.
Den midterste Pig (Hjørnepiggen), der i Regelen er
kortere end Sidepiggene, har en mere afrundet Form og
bærer paa sin Ende en Slags Pedicellaria, der er
fritstaaende og fæstet til Piggen ved en elastisk Stilk, hvori
findes stærke Muskelfibre, der dirigere Bevægelsen, Fig. 5,
b. 6, e.
Den nævnte Pedicellaria rager et godt Stykke op over
Furepiggene og strækker sig udover Ambulacralfuren. Den
er langstrakt, 2""" lang; dens frie Ende, 0.81""" bred, er
afrundet, imedens Stilken, der er fæstet til Piggen, er
temmelig smal, næsten rund, 0.40""" tyk, Fig. 6.
Pedicellariens Skelet dannes af en aflang, tyk
Kalkplade, som forneden er temmelig smal og bliver
næsten rund, hvor den ender, Fig. 7, a. Strax ovenfor
Basaldelen udvider Kalkpladen sig vingeformigt til den ene
Side, Fig. 7, b, og faar sin største Udvidning paa dens
øverste Del, hvor der iagttages en Fure, Fig. 7, c, som
strækker sig nedover den indvendige, lidt konkave Rand (den,
der vender mod Ambulacralfuren) til henimod dennes
nederste Trediedel, Fig. 7, d, imedens den paa den
udvendige, noget konvexe Rand, kun strækker sig lidt nedover
dennes øverste Trediedel, Fig. 7, e. Kalkpladens
Sideflader, Fig. 7, /, ere stærkt konvexe.
Dette Kalkskelet er sammensat af et massivt
Kalknet, hvoraf enkelte Bjelker rage udover Randene og danne
her kantede Pigge (Tænder), Fig. 7, g.
Kalkskelettet er indesluttet af en tynd, halv
gjennem-sigtig Membran, hvori hist og her yderst fine Kalkkorn
ere henstrøede, Fig. 6. Membranen slutter tæt til
Kalkpladens Sider, medens den viger et godt Stykke fra dens
udvendige Rand, saaledes at der imellem denne og
Membranen bliver et lidet Rum, Fig, 6, a.
Den før beskrevne Fure paa Kalkpladen er beklædt
med en tyk, gulhvid Hud, der hvælver sig op over dens
Rande og danner paa hver Side en stærkt fremstaaende
Læbe, Fig. 6, b, som forlænger sig nedover paa
Kalkpladens indvendige og udvendige Rand, saa langt som Furen
strækker. Disse Læber have paa deres frie, hvælvede
Rande, som ere noget bugtede, en Liste, Fig. 6, c, der
gjør Læberne paa dette Sted tykkere og fastere. Naar
Læberne ere sluttede, opstaar en temmelig stor Hulhed,
hvis Bund dannes af Kalkpladens Fure; vige Læberne fra
are placed in a triangular form. There are 7 spines
altogether, and one of them is placed at the apex of the
triangle, next to the furrow; whilst, the other six spines
are distributed, three, upon each of the containing sides
(fig. 4, a, 5, a).
The three lateral spines (occasionally, however, four
spines may be observed upon one of the sides) are
flattened, and their free extremities are rather acute, besides
being aculeated.
The mesial spine (the apex spine) is, usually, shorter
than the lateral spines, and has a more rounded form. It
carries upon its extremity, a kind of pedicellaria, which
is isolated, but secured to the spine by an elastic peduncle,
in which strong muscular fibres, that serve to direct the
movements, are seen (fig. b. 6, e).
The pedicellaria referred to, projects considerably
above the furrow spines, and extends across the ambulacral
furrow. It is elongate, 2""" in length, and has a
rounded free extremity, 0.81mm broad, whilst, the peduncle
secured to the spine, is rather narrow, almost round, and
0.40»"" thick (fig. 6).
The skeleton of the pedicellaria is formed of an
oblong thick calcareous plate, whose lower part is rather
narrow, and becomes almost round at the termination (fig.
7, a). Immediately above the basal part, the plate
expands to one side, in the form of a wing (fig. 7, b) and
becomes widest in the superior part. A furrow (fig. 7, c)
occurs here, extending down over the interior
somewhat concave, margin (that, facing towards the ambulacral
furrow) until about the inferior third part (fig. 7, d), whilst,
upon the exterior somewhat convex margin, it only
extends a little down over the superior third part (fig. 7, e).
The lateral surfaces of the calcareous plates (fig. 7,/) are
strongly convex.
The skeleton is composed of a massive calcareous
reticulation, of which, some rods project beyond the margins,
and form, here, plane-sided spines (Teeth) (fig. 7,g).
The calcareous skeleton is enclosed by a thin
semi-translucent membrane, in which, extremely minute
calcareous grains, are here and there overstrewed (fig. 6). The
membrane closes immediately to the interior margin ol the
calcareous plate, whilst, on the exterior margin, it is placed
at a considerable distance from it, so, that between the
membrane and the exerior margin of the plate, a small
interspace is left (fig. 6, a).
The previously described furrow on the calcareous
plate, is covered with a thick yellowish-white integument,
which becomes swollen up, over and above the margins,
forming on each margin, a strongly protuberant labia (fig.
6, b) which extends downwards, on the exterior and
interior margin of the calcareous plate, as far as the furrow
extends. These labiæ, have, upon their free arcuate
margins, which, also, are somewhat curved; a fillet (fig. 6, c),
which causes the labiæ, to become in this situation, thicker
and firmer. When the labiæ are closed, a tolerably large
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