116 



Fam. Limnetidæ. 



Character. — Skallen stærkt huget, Valvlerne 

 Ilden Væxtstriber og forbundne dorsalt med en 

 iTfuldkommen Laas. Hovedet af enorm Storrelse, 

 gaaende nd i et nedadkrummet Rostrum af for- 

 skjellig Form hos de to Kjon. Triinciis forholdsvis 

 kort og massiv; Halen rudimentær. Iste Par Folere 

 smaa og simple; 2det Par forholdsvis korte, men 

 kraftige. Kindljakkernes T^'ggedel stumpt tandet. 

 2det Par Kjæver rudimentære. Foddernes Antal 

 ikke overstigende 12 Par; de ydre Enditer finger- 

 formigt forlængede; kun l.ste Par hos Hannen 

 prehensile. Forplantningen udpræget bisexuel. Ud- 

 viklingen en compliceret Metamorphose, begyndende 

 med et eiendommeligt Naupliusstadium. 



Bemærkninger. — Denne Familie er kiin ba- 

 seret paa en enkelt Slægt, Limnetis, som dog synes 

 mig i saa mange væsentlige Punkter at afvige fra 

 de til foregaaende Familie henregnede Slægter, at 

 den fortjener at udskilles fra samme. Af Packard 

 er den ogsaa op.stillet som Typen for den ene af de 

 2 Underfamilier, hvori hans Familie Limnadiadæ 

 deles. Bet fortjener dog her at nævnes, at den til 

 foregaaende Familie horende Slægt Cydestheria i 

 visse Forhold synes at vise en Tilnærmelse til nær- 

 værende Familie, uden at den dog kan henregnes 

 til samme. 



Fam. Limnetidæ. 



Gen. Limnetis, Loven, 1846. 



Sijn. Hcdessa Lievin. 



Slægtscharacter. — Skallen mere eller mindre 

 kugleformig, glat, uden tydelige Umboner. Hovedet 

 kjolet efter Midten og forlænget til et hos Hunnen 

 mere eller mindre tilspidset, hos Hannen tvært af- 

 kuttet Rosti'um; til Siderne af Hovedet en vel ud- 

 viklet bueformig Fornix. Haledelen meget liden, 

 ikke omboiet og nden tandede Plader, men dækket 

 nedenunder af en operkelformig Lamelle. Umiddel- 

 bart foran den hos Hunnen 2 fra den dorsale Flade 

 af Truncus udgaaende bladformige Plader. De sam- 

 mensatte Øie sammensmeltede i Midten. Det enkle 

 Øie vel udviklet, Ijeliggende nær de sammensatte 

 Øine. Foran dem 2 tæt sammen.stillede eilierede 

 Feldter. Iste Par Følere kolleformige ; 2det Par 

 med Grenene neppe længere end Skaftet og delte i 

 talrige korte Led, hvert kun bærende en enkelt 

 Svommeborste i Bagkanten. Overlæben simpel, uden 

 nogen tentakelformig Fortsats. 2det Par Kjæver 



Characters. — Shell very tumid; the valve.s 

 without lines of growth, and connected dorsally by 

 an imperfect hinge. Head of enormous size, ending in 

 a downward-curved rostrum of a different form in the 

 two sexes. Trunk comparatively short and massive ; 

 tail rudimentary. First pair of antennæ small and 

 simple; 2nd pair comparatively short, but jiowerful. 

 The masticatory part of the mandibles bluntly den- 

 tated. Second pair of maxillæ rudimentary. Num- 

 hev of legs not exceeding 12 pairs; the outer endites 

 digitiformly prodxiced; only the 1st pair in the male 

 prehensile. Propagation markedly bi-sexual. Deve- 

 lopment a complicated metamorphosis, beginning 

 with a ]ieculiar nau]ilius stage. 



Remarks. — This family is based upon only a 

 single genus, Limnetis, which yet seems to me to 

 differ in so many essential points from the genera be- 

 longing to the foregoing family, that it merits being 

 separated from them. It has also been established 

 by Packard as the type of one of the 2 sub-families, 

 into which his family Limnadiadæ is divided. It is, 

 however, deserving of mention here that the genus 

 Cydestheria, belonging to the foregoing family, seems, 

 in certain points, to approach the present family, 

 though it cannot be classed under it. 



Gen. Limnetis, Loven, 1846. 



Syu. Hedrssa Lievin. 



Generic Characters. — Shell more or less sphe- 

 rical, smooth, and without distinct umbones. Head 

 carinated medially, and produced in the female to a 

 more or less jjointed rostrum, in the male to one 

 abruptly triincated; at the sides of the head a well- 

 developed arcuate fornix. Caudal part very small, 

 not bent downwards, and without dentated lamellæ, 

 but covered beneath by an opercular lamella. Imme- 

 diately^ in front of it in the female, there are two 

 foliate lamellæ issuing from the dorsal surface of 

 the trunk. The compound eyes merged together in 

 the middle. Ocellus well-developed, situated near 

 the compound eyes. In front of tliem two juxta- 

 posed, ciliated fields. First pair of antennæ cla- 

 vate; 2nd pair with the rami scarcely longer 

 than the scape, the former composed of niimerous 

 short joints, each carrying only a single natatory 

 bristle on tlie hind margin. Labrum simple, witiiout 



