242 
betydelig storre end den halve Lsengde. Apex er forholdsvis 
kun lidet fremspringendc og udgaar ne den under Kropsaxen 
eller i nogenlunde lige Flugt mod Aabningsranden (margo 
occludens). Som saedvanlig dmkkes Oapitulum af 14 Kalk- 
stykker eller Yalvler, 2 uparrede og 6 parreda. De er 
alle tydeligt begreendsede og skilte ved smale mellemliggende 
Hudstriber. Overfladen af Yalvlerne er nsesten ganske glut, 
eller kun forsynet med svagt udprfegede concentriske og 
endnu utydeligere rad i acre Striber. 
Kjolen (carina), der dannes af den dorsale uparrede 
Yalvel, er vel udviklet og temmelig hoi samt visor sig 
tydeligt at bestaa af 5 med hverandre fast forbundne Stykker, 
et smalt uparret i Midten (tectum) og 2 parrede Sidestykker 
(parietas og intra-parietas). Den er i sit ydre Parti stamkt 
vinkelformigt boiet, med en tydeligt udprmget Umbo, der 
paa Grand at Apex’s Korthed ligger n for mere denne end 
Basis af Oapitulum. 
Tergalstykkerne (terga), der tilsammen danner den 
saakaldte Apex, er af smal uligesidet trkcnguher Form, med 
Aabningsranden (margo occludens) betydelig kortere end 
nogen af de 2 ovrige. Den dorsale spidst udlobende Ende 
at disse Stykker ligger indkilet mellem Kjolen og de ovre 
Sidestykker. 
Skjoldene (scuta), der til liver Side begrsendser det 
nedre Parti at Skallens Aabning, er af uregelmaessig fir- 
kantet Form og uden nogen tydeligt udprseget Umbo. Af 
de 4 Sider er den frie mod Skallens Aabning vendte 
Lengst, de 3 ovrige nmsten af ens Laengde. 
De Ovre Sidestykker (latera superiora), der omtrent 
indtager Midten af Oapitulums Sider og foruden af de oven- 
naevnte Yalvler tillige begraendses af 2 af Basalstykkerne, 
er vistnok mindre end Skjoldene, men neppe smalere, skjaevt 
5-kantede og forsynede med . en meget tydelig subcentral 
Umbo. 
De basale Sidestykker, der umiddelbart stoder op til 
Stilken, danner tilsammen en Tvaerrad, der indtager hele 
Oapitulums Brede og skiller sig fra hverandre baade i Stor- 
relse og Form. De dorsale Stykker (latera carinalia), der 
omfattei mellem sig den basale Del at Kjolen, er storst 
og af en noget uregelmaessig a,flang Form, med det basale 
Hjorne noget fremspringende og opadkruinmet. De midterste 
Basalstykker (latera infero-mediana) er 5-kantede, omtrent 
lige brede ved Basis som ved Apex, der dannes af de 2 
korteste Sider. De ventrale Basalstykker (latera rostralia) 
or uregelimessigt 4-kantede, med den basale Side kortest, 
den apicale lasngst. 
Rostrum (se Fig. 2), der danner den ventrale uparrede 
Valvel og ligger indkilet mellem de 2 ventrale Basalstykker, 
er vistnok den mindste af alle Yalvlerne, men dog betydelig I 
storre end hos Sc. vulgare, hvor det er ganske og aldeles 
rudnnentmrt. At Form or det pyramidalt eller kiledannet, 
bredest ved Basis og jevnt afsmalnende mod Spidsen, der 
i.ekkei til Enden at de ventrale Basalstykker og begrsendser 
Skalaabningen i Midten. 
towards the extremity, with the breadth considerably ex- 
ceeding half the length. The apex, projecting comparatively 
but little, juts out beneath the axis ot the body, or well-nigh 
in' a line with the occluding margin (margo occludens). As 
usual, the capitulum is covered by 1 4 calcareous segments, 
or valves, 2 odd and 6 even. They are all distinctly marked 
off, and separated by narrow intervening cutaneous strips. 
Ihe surface of the valves is almost entirely smooth, or 
exhibits merely faint concentric lines and still more indis- 
tinct radial striae. 
The keel (carina), formed by the odd dorsal valve, 
is well developed, and rather high, as also distinctly seen 
to consist of 5 segments, firmly connected together, viz. — 
a narrow, odd segment in the middle (tectum) and 2 even 
lateral segments (parietas and intra-parietas). Its outer 
pait- exhibits a sharp angular bend, with a prominent umbo, 
which, owing to the shortness of the apex, lies nearer to 
the latter than to the base ot the capitulum. 
The tergal segments (terga), forming together the so- 
called apex, lias a narrow, inecpiilateral-triangular form, 
with the occluding margin (margo occludens) considerably 
shorter than either ot the 2 others. The dorsal, acutely 
protruding extremity of these segments, lies wedged in be- 
tween the keel and the upper lateral segments. 
I he shields (scuta), which, on either side, limit the 
lower part ot the opening in the shell, have an irregular- 
quadi atic form, without any distinctly prominent umbo. Ot 
the 4 sides, that occurring tree and turned towards the 
opening in the shell is longest, the remaining 3 are well- 
nigh equal in length. 
I ho upper lateral segments (latera superiora), occupy- 
ing about the middle of the sides of the capitulum and 
defined, exclusive of the forementioned valves, also by 2 of 
the basal, are indeed smaller than the shields, but scarcely 
narrower, oblique-pentagonal in form, and furnished with 
a well-marked .subcentral umbo. 
The basal lateral segments, adjoining the peduncle, 
constitute a transverse series, occupying the entire breadth 
of the capitulum, and differ alike in size and in form. The 
dorsal segments (latera carinalia), which embrace the basal 
part ot the keel, are largest, and of a somewhat irregular- 
oblong form, with the basal corner slightly projected and 
curving upward. The median basal segments (latera infero- 
mediana) are pentagonal, about equally broad at the base 
and at the apex, with the latter formed by the 2 shortest of 
the sides. The ventral basal segments (latera rostralia) 
are irregular-quadratic, having the basal side the shorter, the 
apical the longer. 
Ihe rostrum (see fig. 2), that forms the ventral odd 
valve, and lies wedged in between the 2 ventral basal seg- 
ments, is indeed the smallest valve of all, but nevertheless 
considerably larger than the corresponding part in Sc. vul- 
gare, which occurs quite rudimentary. Inform, the rostrum 
is pyramidal or wedge-shaped, broadest at the base, and 
tapers gradually toward the point, that reaches the ex- 
| treniity ot the ventral basal segments and defines the open- 
ing oi the shell in the middle. 
