116 



Fam. Limnetidæ. 



Character. — Skallen stærkt huget, Valvlenie 

 nåen Væxtstriber og forbundne dorsalt med en 

 nfuldkommen Laas. Hovedet af enorm Størrelse, 

 gaaende nd i et nedadkrummet Rostrum af for- 

 skjellig Form hos de to Kjon. Trnncus forholdsvis 

 kort og massiv; Halen rudimentær. 1 ste Par Folere 

 smaa og simple; 2det Par forholdsvis korte, men 

 kraftige. Kindbakkernes Tyggedel stumpt tandet. 

 2det Par Ivjæver rudimentære. Foddernes Antal 

 ikke overstigende 12 Par; de ydre Enditer finger- 

 formigt forlængede; kun Iste Par hos "Hannen 

 ])rehensile. Forplantningen udpræget l)isexuel. Ud- 

 viklingen en compliceret iletamorphose, liegyndehde 

 med et eiendommeligt NaupUusstadium. 



Bemærkninger. — Denne Familie er kiin ba- 

 seret paa en enkelt Slægt, Limnetis, som dog synes 

 mig i saa mange væsentKge Punkter at afvige fra 

 de til foregaaende Familie henregnede Slægter, at 

 den fortjener at udskilles fra samme. Af Packard 

 er den ogsaa opstillet som Typen for den ene af de 

 2 Underfamilier, hvori hans Familie LimuadiadfP 

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

 foregaaende Familie horende Slægt Cydestheria i 

 visse Forhold .';ynes at vise en Tilnærmelse til nær- 

 værende Familie, uden at den dog kan henregnes 

 til samme. 



Gen. Limnetis, Loven, i84(J. 



Syn. Hedessa Licvin. 



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 Po.stnim; til Siderne af Hovedet, en vel ud- 

 viklet bueformig Fornix, Haledelen meget liden, 

 ikke omboiet og uden taiulede Plader, men dækket 

 nedeniinder af en operkelformig LameUe. Umiddel- 

 bart foran den hos Hunnen 2 fra den dorsale Flade 

 af Truncus udgaaendo bladformige li'lader. De sam- 

 mensatte Øie sammensmeltede i Midten. Det enkle 

 Øie vel udviklet, beliggende nær de sammensatte 

 Øine. Foran dem 2 tæt sammenstillede eilierede 

 Feldter. Iste Par Folere kolleformige; 2det Par 

 med Grenene nep])e længere end Skaftet og delte i 

 talrige korte Ijed, hvert kun bærende en enkelt 

 Svømmeborste i Bagkanten. Overla-ben simpel, uden 

 nogen tentakelformig Fortsats. 2det Par Kjæver 



Fam. Limnetidæ. 



Characters. — Shell very tumid; the valves 

 without lines of growth, and connected dorsally by 

 an imperfect hinge. Head of enormous size, ending in 

 a downward-curved rostrum of a ditferent form in the 

 two sexes. Trunk comparatively short and mas.sive ; 

 tail rudimentaiy. First ])air of antennæ small aud 

 simple; 2nd pair comparatively short, but powerful. 

 The masticatory part of the mandibles Iduntly den- 

 tated. Second pair of maxillæ rudimentary. Num- 

 ber of legs not exceeding 12 pairs; the (uiter endites 

 digitiformly prodiTced; only the 1st pair in the male 

 prehen.sile. Propagation markedly bi-sexual. Deve- 

 lopment a complicated metamorphosis, beginning 

 with a ])eculiar nauplius stage. 



Remarks. — This family is based upon onljr a 

 single genus, Limnetis. which yet seems to mé to 

 differ in so many essential jjoints 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 Livmadiadæ 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. 



Siju. HidesSli Licvin. 



Generic Characters. — Shell more or less s])he- 

 rieal, sinuoth, and without distinct umbones. Head 

 carinated medially, and produced in the female to a 

 more (U" less pointed rostrum, in the male to one 

 abru])tly truncated; at the sides of the head a w^ell- 

 developed arcuate fornix. Caudal pai't very small, 

 not bent downwards, and without dentated lamellæ, 

 but covered beneath b}' 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 I'ront of them two juxta-- 

 l)0sed, ciliated Helds. First pair of antennæ (da- 

 vate; 2nd pair with tlie rami scarcely longer 

 than the scape, the former composed ot numerous 

 short joints, each carrying only a single natatory 

 bristle on the hind margin. Labrum simple, without 



