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; 
: 
123 
Overleben (Fig. 11, Z), som danner den umiddel- 
bare Fortsettelse af Hovedets ventrale Flade, er af 
betydelig Storrelse og rekker ind mellem Basis af 
Iste, tildels endogsaa 2det Fodpar. Den har For- 
men af en aflang, noget sammentrykt Lap, der i sit 
ydre Parti danner en noget nedadboiet, rundtom 
fint cilieret oval Lamelle, uden nogen saadan ten- 
takelformig Fortsats som hos Limnadia. Overleben 
kan loftes af fra Munddelene ved et Par tynde 
Muskler, der fra Hovedets Integument passerer til 
dens Basis. I dens Indre sees, som hos Limnadia, 
flere celleagtige Legemer og et Antal af tvergaaende 
Muskler, som virker paa dens ovre blode og rende- 
formigt fordybede Flade. 
Kindbakkerne (Fig. 4, Fig. 11, M) ligger, som 
hos Limnadia, i Form af 2 boileformige Legemer til 
hver Side paa Grendsen mellem Hovedet og Nakke- 
segmentet. Deres ovre tilspidsede Ende er articu- 
leret til et fortykket Parti af Integumentet ved 
Enderne af den mellem begge de ovenneevnte Dele 
gaaende T'veersutur, medens deres nedre, steerkt ind- 
boiede Ender modes paa Undersiden ved Mundaab- 
ningen. Tyggedelen er stwrkt, nesten oxeformigt 
udvidet, og viser en noget tilskjerpet Kant delt i 
en Rekke stumpe Tender, hvoraf den yderste er 
storst. I sin Bevebning skiller altsaa Kindbakkerne 
hos nerverende Form sig meget vesentligt fra 
samme hos de ovrige bivalve Phyllopoder og viser 
en Tilnermelse til den for Apodiderne characteristiske 
Bygning. 
Forste Par Kjever (Fig. 4, 11, m*, Fig. 5), be- 
staar, som hos Limnadia, af en tykkere Basaldel og 
en beveegelig Endeplade; men denne sidste er her 
betydelig smalere, leformigt indadkrummet, og kun 
forsynet med et begrendset Antal af sterke, uled- 
dede Borster. Langs den indre Kant af Pladen tel- 
ler man 8 saadanne Borster, noget tiltagende i 
Lengde udad og fint cilierede i den ene Kant (se 
Fig. 5a). Ved Spidsen af Pladen er festet 3 be- 
tydelig kortere Borster, der er pigformige og grovt 
tandede i begge Kanter (se Fig. 5b). I den ydre 
Kant har Pladen ved Basis en meget fin Ciliering. 
Andet Par Kjever (Fig. 4, 11, m*, Fig. 6), der 
ikke er bemerkede af Grube, er meget rudimentere, 
kun forestillende et Par simple, noget hjertefcrmige 
Lameller af en delikat membranos Beskaffenhed, i 
hvilken Henseende de nermest synes at svare til 
den ydre Udvidning (Palpe) af disse Kjever hos 
Lepidurus. Deres Beliggenhed, temmelig langt fijer- 
nede fra Midtlinien (se Fig. 4), taler ogsaa for en 
saadan Tydning, hvorved altsaa den egentlige Tygge- 
del maa antages at vere ganske oblitereret. Lamel- 
the scape. In the outer part of the latter, other 
muscles are visible, which act upon each of the 
rami. 
The labrum (fig. 11, Z), which forms an imme- 
diate continuation of the ventral surface of the 
head, is of considerable size, and extends between 
the bases of the 1st, and partly also of the 2nd 
pair of legs. It has the form of an oblong, ra- 
ther compressed lobe, whose outer part forms a 
somewhat downward-curved, oval lamella, finely 
ciliated all round, and without any such tentacular 
projection as in Limnadia. The labrum can be 
raised from the oral parts by a pair of thin muscles 
passing to its base from the integument of the head. 
In its interior may be seen, as in Limnadia, several 
cellular bodies, and a number of transverse mus- 
cles, acting upon its upper soft and grooved surface. 
The mandibles (fig. 4, fig. 11, JZ) lie, as in Lim- 
nadia, in the shape of 2 bow-shaped bodies, one on 
each side, at the boundary between the head and 
the cervical segment. Their upper pointed end is 
articulated to a thickened part of the integument, 
at the ends of the transverse suture which runs 
between the two parts just named; while their 
lower, much incurved ends meet on the under sur- 
face at the oral aperture. The masticatory part 
is strong, and almost securiformly expanded, and 
exhibits a somewhat sharpened edge, divided into a 
series of blunt teeth, the outermost of which is the 
largest. Thus, in the matter of equipment, the man- 
dibles in this form are very essentially distinct 
from those in the other bi-valve Phyllopoda, and 
show an approach to the structure characteristic of 
the Apodide. 
The ist pair of maxille (figs. 4, 11, m'*, fig. 5) 
consist, as in Limnadia, of a thicker basal part and 
a movable terminal lamella; but the latter is here 
considerably narrower, is curved falciformly inwards, 
and furnished with only a limited number of strong, 
unarticulated bristles. Along the inner edge of the 
lamella, 8 such bristles may be counted, somewhat 
increasing in length outwards, and finely ciliated on 
one edge (see fig. 5a). To the point of the lamella 
are attached 3 considerably shorter bristles, which 
are spiniform and coarsely dentated on both edges 
(see fig. 5b), At its base the lamella is very finely 
ciliated on the outer margin. 
The second pair of maxille (figs. 4, 11, m’, 
fig. 6), which have not been observed by Grube, 
are very rudimentary, representing only a pair of 
simple, somewhat cordate lamelle of a delicate, 
membranous consistency, in which respect they seem 
almost to correspond to the outer expansion (palp) 
of these maxille in Lepidurus. Their position, at 
some distance from the median line (see fig. 4), also 
favours such an interpretation, whereby the true 
masticatory part must be assumed to be quite 
