123 



Overlæben (Fig. ll.Z), sora danner den umiddel- 

 liare Fortsættelse af Hovedets ventrale Flade, er af 

 betydelig Storrelse og rækker ind mellem Basis af 

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

 men af en aflang, noget sammeiitrykt Lap, der i sit 

 ydre Parti danner en noget nedadboiet, rundtom 

 rint cilieret oval Lamelle, nden nogen saadan ten- 

 takelformig Fortsats som hoa Limnadia. Overlæben 

 kan loftes af fra Mi^nddelene ved et Par tynde 

 Muskler, der fra Hovedets Integument passerer til 

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

 flei'e celleagtige Legemer og et Antal af tværgaaende 

 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 Grændsen mellem Hovedet og Nakke- 

 segmentet. Deres ovre tilspidsede Ende er artieu- 

 leret til et fortj'kket Parti af Integumentet ved 

 Enderne af den mellem begge de ovennævnte Dele 

 gaaende Tværsutur, medens deres nedre, stærkt ind- 

 boiede Ender modes paa Undersiden ved Mundaab- 

 ningen. Tyggedelen er stærkt, næsten oxeformigt 

 udvidet, og viser en noget tilskjærpet Kant delt i 

 en Rsekke stumpe Tænder, hvoraf den yderste er 

 størst. I sin Bevæbning skiller altsaa Kindbakkerne 

 hos nærværende Form sig meget væsentligt fra 

 samme hos de ovrige bivalve Phyllopoder og viser 

 en Tilnærmelse til den for Apodiderne characteristiske 

 Bygning. 



Forste Par Kjæver (Fig. 4, 11, «; \ Fig. 5), be- 

 staar, som hos Limnadia, af en tykkere Basaldel og 

 en bevægelig Endeplade; men denne sidste er her 

 betydelig smalere, leformigt indadkrnmmet, og kun 

 forsynet med et begrændset Antal af stærke, uled- 

 dede Borster. Langs den indre Kant af Pladen tæl- 

 ler man S saadanne Borster, noget tiltagende i 

 Længde udåd og fint cilierede i den ene Kant (se 

 Fig. 5 a). Ved Spidsen af Pladen er fæstet 3 be- 

 tydelig kortere Borster, der er pigformige og grovt 

 tandede i begge Kanter (se Fig. 5 b). I den ydre 

 Kant har Pladen ved Basis en meget fin Ciliering. 



Andet Par Kjæver (Fig. 4, 11, m-'\ Fig. (3), der 

 ikke er bemærkede af Grube, er meget rudimentære, 

 kun forestillende et Par simple, noget hjertefcrmige 

 Lameller af en delikat membranos Beskaffenhed, i 

 hvilken Henseende de nærmest synes at svare til 

 den ydre Udvidning (Palpe) af disse Kjæver hos 

 Lepiduriis. Deres Beliggenhed, temmelig langt fjer- 

 nede fra Midtlinien (se Fig. 4), taler ogsaa for en 

 saadan Tydning, hvorved altsaa den egentlige Tygge- 

 del maa antages at være ganske oblitereret. Lamel- 



the scape, ln the outer part of the latter, other 

 muscles are visible, which act upon each of the 

 rami. 



The labrum (fig. 11, L). 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 integiiment of the head. 

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

 cellular bodies, and a number of transverse mwa- 

 cles, acting upon its upper soft and grooved surface. 

 The mandibles (fig. 4, fig. 11, ilf) 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 sxiture 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 In-valve Phyllopoda, and 

 show an approach to the structure characteristic of 

 the Apodid(P. 



The 1st pair of maxillæ (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. 5 a). To the point of the lamella 

 are attached 3 considerably .shorter bristles, which 

 are spiuiform and coarsely dentated on both edges 

 (see fig. 5 b). At its base the lamella is very finely 

 ciliated on the outer margin. 



The second pair of maxillæ (figs. 4, 11, w^ 

 fig, 6), which have not been observed by (Trube, 

 are very rudimentary, representing only a pair of 

 simple, somewhat cordate lamellæ of a delicate, 

 membranous consistency, in which respect they seem 

 almost to correspond to the outer expansion (palp) 

 of these maxillæ 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 cpite 



