123 



Overlæben (Fig. 11, Z), som danner don umiddel- 

 Ijare Fortsættelse af Hovedets ventrale Flade, er af 

 betydelig Storrelse og rækker ind mellera Basis af 

 Iste, tildels endogsaa 2det Fodpar. Den har For- 

 men af en aflang. noget sammentrvkt Lap, der i sit 

 ydre Parti danner en noget nedadboiet, rnndtoni 

 fint cilieret oval Lamelle, uden nogen saadan ten- 

 takelformig Fortsats som bos Limnadia. Overlæben 

 kan løftes af fra Mnnddelene ved et Par tj-nde 

 Muskler, der fra Hovedets Integnment passerer til 

 dens Basis. I dens Indre sees, som hos Limnadia. 

 flere celleagiige Legemer og et Antal af tværgaaende 

 Muskler, som virker paa dens ovre blode og rende- 

 formigt fordybede Flade. 



Kindbakkerne (Fig. 4, Fig. 11, 3/) ligger, som 

 hos Limnadia. i Form af 2 boileformige Legemer til 

 hver Side paa (rrændsen mellem Hovedet og Nakke- 

 segmentet. Deres ovre tilspidsede Ende er artieu- 

 leret til et fortvkket Parti af Integumentet ved 

 Enderne af den mellem begge de ovennævnte Dele 

 gaaende Tværsutur. medens deres nedre, stærkt ind- 

 boiede Ender mode.< paa Undersiden ved Mundaab- 

 ningen. Tyggedelen er stærkt, næsten oxeformigt 

 udvidet, og viser en noget tilskjærpet Kant delt i 

 en Række stumpe Tænder, hvoraf den yderste er 

 storst. I sin Bevæbning skiller altsaa Kindbakkerne 

 hos nærværende Form sig meget væsentligt fra 

 samme hos de ovrige bivalve 1'hylhipoder og viser 

 en Tilnærmelse til den f(<v Apodiderne characteristiske 

 B^-gning. 



Forste Par Kjæ.ver (Fig. 4, 11. m \ Fig. 5), be- 

 staar, som hos Limnadia, af en tykkere Basaldel og 

 en bevægelig Endeplade; men denne sidste er her 

 betydelig smalei-e, leformigt indadkrummet, og kun 

 forsynet med et begrændset Antal af stærke, uled- 

 dede Borster. Langs den indre Kant af Pladen tæl- 

 ler man 8 saadanne Borster, noget tiltagende i 

 Længde udåd og tint eilierede i den ene Kant (se 

 Fig. o a). Ved Spidsen af Pladen er fæ.stet 3 be- 

 tydelig kortere Borster, der er ])igformige og gro\t 

 tandede i begge Kanter (se Fig. o b). 1 den ydre 

 Kant liar Pladen ved liasis en meget fin Ciliering. 



Andet Par Kjæver (Fig. 4, 11, m'\ Fig. 6), der 

 ikke er bemærkede af (Trube, er meget rudimentære, 

 kun forestillende et Par sim])le, noget hjertefcrniige 

 l,ameller af en delikat membranos Beskaftenhed, i 

 hvilken Henseende de n;rrmest synes at svare til 

 den ydre Udvidning (1'alpe) af disse i\jii>ver hos 

 Lepiditrus. Deres Beliggenhed, temmelig langt fjer- 

 nede fra ]\[idtlinien (se Fig. 4), taler ogsaa for en 

 saadan Tydning, hvorved altsaa den egentlige Tygge- 

 del maa antages at være ganske oblitereret. Lamel- 



the seape. ln the outer part of the latter, otlier 

 muscles are visible, wliioh aet u])on each of the 

 rami. 



'i'lie labrum (fig. 11, L). whioli 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 fonn 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 

 ]3assing to its base from the integument of the head. 

 In its interior may be seen, as in Limnadia, several 

 cellular liodies. and a number of transverse mus- 

 cles, acting upon its upper soft and grooved surface. 

 The mandibles (fig. 4, fig. 11, 3/) 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 a])erture. The masticatory part 

 is strong, and almost .seeuriformly expanded, and 

 exhibits a somewhat sharpened edge, divided into a 

 series of blunt teeth, the outermost of which is tlie 

 largest. Thus, in the matter of eipiipment, the man- 

 diljles in this form are very essentially distinct 

 from those in the other bi-valve Phyllopoda. and 

 show an apjiroach to the structitre characteristic of 

 the ApodidfT. 



The 1st pair of maxillæ (figs. 4. 11, m ^ tig. o) 

 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 fineh" ciliated on 

 one edge (see fig. o a). To the point of the lamella 

 are attached 3 considerably shorter bristles, which 

 are spiniform and coarsely dentated on both edges 

 (see fig. h b). At its base the lamella is very finel^y 

 ciliated on the outer margin. 



The second pair of maxillæ (figs. 4. 11, m', 

 fig. li), which have not been observed by Grube, 

 are very rudimentary, representing only a jiair of 

 simjile, somewliat cordate lamellæ of a delicate, 

 membranous consistency, in which respect they seem 

 ahnost to correspond to the outer expan.*ion {pal]i) 

 of these maxillæ in Lopidurus. Their position, at 

 some distance from the median line (see fig. 4). also 

 favours such an interpretation, whereby the true 

 masticatory jiart must be assumed to be (ptite 



