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246
Kalkskjæl. Den ydre Beklædningsiuenibran overalt ru af
fine Smaapigge. Farven ensformig hvid. Længden indtil
35""".
Findesteder. Ståt. 18, 35, 312.
Bemærkninger. Denne anselige Fonn er strax
kjendelig fra de 2 foregaaende Arter, foruden ved sin
betydelige Størrelse, ved den overalt af fine Smaapigge ru ydre
Beklædningshinde og ved den særdeles tydelige og elegante
Sculptur af Skallens Valvler. hvilket har givet Anledning
til Artsbeuævnelsen,
Beskrivelse. Legemet er (se PI. XX, Fig. 5 & 6)
forholdsvis kort og undersætsigt, med Capitulum betydelig
baade længere og bredere end Stilken. Det har en
lignende Stilling i Forhold til de Gjenstande, hvortil det er
fæstet som hos Sc. angustum, idet Stilken ingen mærkbar
Boining viser.
Capitulum er seet fra Siden (Fig. 5) temmelig
regelmæssigt ovalt eller elliptiskt. mere end dobbelt saa langt
som bredt, med den ventrale Rand jevnt buet og Apex
forholdsvis kort, men skarpt tilspidset og noget opadkrummet
samt beliggende næsten noiagtig i Skallens Axe. Valvlerne
er indbyrdes meget fast forbundne, idet de stode
umiddelbart op til hverandre og kun er skilte ved smale, tildels
utydelige Suturer. De viser alle en meget skarpt udpræget
og elegant Sculptur, idet der foruden concentriske
Væxt-striber findes talrige, tildels kjølformigt fremspringende
radierende Ribber.
Kjølen er som hos foregaaende Art ganske smal og
jevnt buet, uden nogen tydelig Umbo og fortsætter sig
nedad lige til Stilkens Begyndelse.
Tergalstykkerne er meget store, men har
Aabnings-randen kjendelig kortere end Basalranden.
Skjoldene er forholdsvis smale, og af en lignende
uregelmæssig 4-sidet Form som hos de 2 foregaaende Arter;
dog er Tergalranden her neppe længere end Basalranden
og begge betydelig kortere end Lateralranden. Det apicale
Hjørne er ligesom hos Sc. angustum spidst udtrukket.
De øvre Sidestykker har det dorsale mod Kjolen
vendte Parti noget kileformigt afsmalnende og den ventrale
Rand uregelmæssigt bugtet. De viser en meget tydelig
subcentral Umbo, hvorfra 5 niere .fremspringende Kjole
radierer.
Af Basalstykkerne er de dorsale [temmelig store og
brede, uregelmæssig 4-sidede og viser intet Fremspring ved
Roden; de mellemste Stykker er meget smaa og af en fra
samme hos de 2 foregaaende Arter væsentlig forskjellig
Form, idet de er smalt triangulære eller kileformige, med
Spidsen vendt mod Basis; de ventrale Stykker er mere end
dobbelt saa store og af 4-kantet Fonn.
with large imbricate calcareous scales. Outer investing
membrane everywhere rough, from numberless minute
spike-lets. Colour a uniform white. Length reaching 35""".
Locality. — Stats. 18, 35, 312.
Remarks. — This large and striking form can lie
at once recognized from the 2 preceding species, not only
by its considerable size but also by the outer investing
membrane, rendered everywhere rough from minute
spike-lets, and the very distinct and graceful sculpture on the
valves of the shell, a character that suggested the specific
designation.
Description. — The body (see Pl. XX, figs. 5, 6)
is comparatively short and thickset, with the capitulum
both longer and broader than the peduncle. It has a
position in relation to [the objects whereto it is attached
similar to that in Sc. angustum, the peduncle not
exhibiting any appreciable flexure.
The capitulum, viewed from the side (fig. 5), is
approximately of a regular oval or elliptic form, more than
twice as long as broad, with the ventral margin evenly
arched and the apex comparatively short, but acutely pointed
and curving slightly upward, as also well-nigh coinciding
with the axis of the shell. The valves are very firmly
connected, coming as they do in close contact, with but
narrow and partly indistinct separating sutures. They all
exhibit a very sharply pronounced and graceful sculpture,
a number of keel-like, radiating ribs occurring along with
concentric striæ of growth.
The keel, as in the preceding species, is quite slender
and evenly arched, without any distinct umbo, extending
downward to the commencement of the peduncle.
The tergal segments are very large, but have the
occluding margin appreciably shorter than the basal.
The shields are comparatively narrow, and of a similar,
irregular-quadratic form to those in the 2 preceding
species; the tergal margin, however, is scarcely at all longer
than the basal, and both are much shorter than the
lateral. The apical corner occurs, as in Sc. angustum, acutely
produced.
The upper lateral segments have the dorsal part
turned towards the keel, somewhat cuneiform-tapering, with
the ventral margin irregularly flexuous. They exhibit a very
distinct subcentral umbo, from which radiate 5 more
prominent carinæ.
Of the basal segments, the dorsal are rather large
and broad, irregular-quadratic, and exhibit no projection
at the base; the median segments are very small, and of
a form essentia lly different from that distinguishing the said
parts in the 2 preceding segments, being narrow-triangular
or cuneiform, with the point turned towards the base; the
ventral segments are more than twice as large, and
quadrangular in form.
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