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56
Endelig skulle vi nu beskjæftige os med den af
Professor Verrill nydannede Slægt Lophaster for Solaster
furcifer, Diiben og Koren.
Til Begrundelse af Slægtens Dannelse udtrykker
Verrill sig saaledes: „This species differs so widely
from Solaster in the structure of the skeleton, and the
small development of the disk, as to require the
etab-lishment of a new genus for this type. It is specially
distinguished by the highly developed skeleton of the under
side; differentiated marginal plates; and prominently
reticulated dorsal plates." 1 Prof. Jeffrey Bell er ikke
langtfra at antage, at Slægten Lophaster er vel begrundet, idet
han lægger særdeles megen Vægt paa de „differentiated
marginal plates, one dorso-marginal and one
ventro-marginal." Vi have tidligere indrømmet, at Randpladerne
spille en betydelig Rolle i Slægtskaraktererne, uden at vi
have kunnet erkjende, at de ere afgjørende. Verrill siger,
at Solaster furcifer adskiller sig saa overordentlig fra
Slægten Solaster i Skelettets Bygning og i den lidet udviklede
Skive, at en ny Slægt maa dannes for den; det er
fornemmelig det stærkt udviklede Skelet paa Bugfladen, de
diffe-rentserede Randplader og de iøjnefaldende, retikulerede
Rygplader, som bestemme den nye Slægts Dannelse. Hvad
nu Skivens Størrelse betræffer i Forhold til Armene, saa
varierer dette ganske betydeligt og kommer kun lidet i
Betragtning ved Slægtsbestemmelsen; anderledes forholder
det sig med Skeletbygningen. Vi skulle først omtale
Hudskelettet.
Rygfladens Hudskelet hos Sol. furcifer dannes af et
temmelig tætmasket Kalknet, Tab. IX, Fig. 9, a, b, der
fremkommer derved, at smaa kors- eller x-formede
Kalkplader lægge sine Udløbere paa hverandre; imellem
Maskerne sees en eller flere Tentakelporer, alt eftersom
Masken er liden eller stor. Omtrent den samme Anordning
finder man hos Sol. endeca, men endnu mere ensartet hos
Sol. glacialis, hvor kun Forskjellen er den, at de enkelte
Kalkstykker ere noget stærkere byggede og have noget
kortere Udløbere, hvorved Maskerne blive noget mindre, Tab.
IX, Fig. 5, b, c, end hos Sol. furcifer.
Bugfladens Hudskelet, Tab. IX, Fig. 9, d, som især
fremtræder i Interbrachialrummene, skulde, efter
Ver-rill, være høiere udviklet hos Sol. furcifer; men heri kunne
vi ikke være enige. Bugfladens Kalkplader hos Sol.
furcifer ere mere eller mindre korsformede med korte Arme,
der vel taglagt ligge paa hverandre, men som dog
eftei-la-der smaa, nøgne Rum, imedens Kalkpladerne hos Sol.
glacialis, Tab. IX, Fig. 5, d, der have næsten Korsformen,
1 Notice of recent additions to the Marine Fauna of North
America, by A. E. Verrill. The Amer. Journal of science and arts.
3rd Ser. Vol. XVI, pag. 214.
Finally, we shall now proceed to consider the new genus
Lophaster formed by Prof. Verrill, instead of Solaster
furcifer, Diiben and Koren.
In confirmation of the reasons for the formation of
the genus, Verrill expresses himself thus: „This species"
„differs so widely from Solaster, in the structure of the"
„skeleton, and the small development of the disk, as to"
„require the establishment of a new genus for this type."
„It is specially distinguished by the highly developed skel-"
„eton of the under side; differentiated marginal plates; and"
„prominently reticulated dorsal plates."1 Professor Jeffrey
Bell almost admits that the genus Lophaster is well based,
as he lays particular stress on the „differentiated marginal"
„plates, one dorso-marginal and one ventro-marginal." We
have already admitted, that the marginal plates play a
prominent part in determining generic character, but we
cannot, however, admit, that they are absolutely decisive in
the matter. Verrill states, that Solaster furcifer differs so
verv much from the genus Solaster in regard to the
construction of its skeleton, and in its slightly developed disk,
that a new genus must be formed for it; and, it is
principally. the strongly developed skeleton of the actinal floor;
the differentiated marginal plates; and the prominent,
reticulated dorsal plates, which decide the formation of the
new genus. As far as regards the dimensions of the disk
in proportion to the rays; this varies quite considerably,.
but is a small matter for consideration in deciding the
genus; the case is very different, however, when the
construction of the skeleton is concerned. We shall first speak
of the dermal skeleton.
The abactinal dermal skeleton in Solaster furcifer, is
formed of a rather close-meshed calcareous reticulation,
(Pl. IX, fig. 9, a, b), produced by small X or crucial
formed calcareous plates laying their projections upon each
other. One or more tentacular pores are visible between
the meshes, the number varying, according to the greater
or smaller size of the meshes. A nearly similar
arrangement is found in Solaster endeca, but still more similar
in Solaster glacialis, where, the only difference is, that the
individual calcareous ossicles are somewhat stronger
constructed, and have somewhat shorter projections, causing
the meshes to be somewhat smaller (Pl. IX, fig. 5, b, c)
than in Solaster furcifer.
The abactinal dermal skeleton (Pl. IX, fig. 9, d), is
specially prominent in the interbrachial spaces, and
according to Verrill, it is more highly developed in Solaster
furcifer-, but we cannot share his opinion in regard to this.
The calcareous plates of the actinal surface in Solaster
furcifer, are more or less crucial, with short arms, which,
lie upon each other well imbricated, but still leaving
small bare spaces; whilst, the calcareous plates in Solaster
glacialis (Pl. IX, fig. 5, d), which are also crucial, as well
1 Notice of recent additions to the Marine Fauna of North
America by A. E. Verrill. The Amer. Journal of Science and Arts
3rd Ser. Vol. XVI, pag. 214.
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