116 



Fam. Limnetidæ. 



Character. — Skallen stærkt Iniget, Valvlerne 

 ixden Væxtstriber og forbmiclne dorsalt med en 

 iifuldkommen Laas. Hovedet af enorm Størrelse, 

 gaaende xiå i et nedadkrnmmet Rostrum af for- 

 skjellig Form hos de to Kjon. Trimcus forholdsvis 

 kort og massiv ; Halen rudimentær. 1 ste Par Folere 

 smaa og simple; 2det Par forholdsvis korte, men 

 kraftige. Ivindbakkernes Tyggedel stumpt tandet. 

 2det Par Kjæver rudimentære. Foddernes Antal 

 ikke overstigende 12 Par; de ydre Enditer linger- 

 formig-t forlængede; kun Iste Par hos Hannen 

 prehensile. Forplantningen udpræget bisexuel. Ud- 

 viklingen en compliceret Metamorphose, begjnidende 

 med et eiendommeligt Naupliusstadinm. 



Bemærkninger. — Denne Familie er kun ba- 

 seret paa en enkelt Slægt, Linmetis, 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 opstillet som Typen for den ene af de 

 2 Underfamilier, hvori hans Familie Limuadiadce 

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

 foregaaende Familie horende Slægt Cydestheria i 

 visse Forhold .sj-nes at vise en Tilnærmelse til nær- 

 værende Familie, uden at den dog kan henregnes 

 til samme. 



Gen. Limnetis, Loven, i84(j. 



Syn. Hedcssa Lievin. 



Slægtscharacter. — Skallen mere eller mindre 

 kngleformig, glat, uden tydelige Umboner. Hovedet 

 kjolet efter Midten og Ibrlænget til et hos Hunnen 

 mere eller mindre tilspidset, hos Hannen tvært af- 

 knttet Rostrum; til Siderne af Hovedet en vel ud- 

 viklet Inxeformig Fornix. Haledelen meget liden, 

 ikke omboiet og uden tandede Plader, men dækket 

 nedenunder af en operkelformig Lamelle. Umiddel- 

 bart foran den hos Hunnen 2 Ira den dorsale Flade 

 af Truncus iidgaaende bladformige Plader. De sam- 

 mensatte Øie sammensmeltede i Midten. Det enkle 

 Øie vel udviklet, beliggende nær de sammensatte 

 Øine. Foran dem 2 tæt sammenstillede cilierede 

 Feldter. Iste Par Følere kølleformige ; 2det Par 

 med Grenene neppe længere end Skaftet og delte i 

 talrige korte Led, hvert kun bærende en enkelt 

 Svømmebørste i Bagkanten. Overlæben simpel, iiden 

 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 different form in the 

 two sexes. Trunk comparatively short and massive ; 

 tail rudimentary. First pair of antennæ small and 

 simple; 2nd pair comparatively short, biit powerful. 

 The masticatory part of the mandibles bluntly den- 

 tated. Second jiair of maxillæ rudimentary. Num- 

 ber of legs not exceeding 12 pairs; the outer endites 

 digitiformly produced; only the 1st pair in the male 

 prehensile. Propagation markedly bi-sexual. Deve- 

 lopment a complicated metamorphosis, beginning 

 with a peculiar nanplius 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 

 sepai'ated from them. It has also been established 

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

 into A^'hich his family Limnadiadæ is divided. It is, 

 however, deserving of mention here tliat the genus 

 Gyclestheria, belonging to the foregoing family, seems, 

 in certain points, to approach the present family, 

 thou2:h it cannot be classed under it. 



Gen. Limnetis, Loven, 1846. 



Syn. Hedcssa 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 pointed rostrum, in the male to one 

 abruptly truncated; 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. Tlie compoiind eyes merged together in 

 the middle. Ocellus well-developed, sitiiated near 

 the compound eyes. In front of them 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 numerous 

 short joints, each carrying only a single natatory 

 bristle on the hind margin. Labrum simple, without 





