110 



skiftningen er Valvlerne forsjaiede med nok en 

 Væxtstribe udenom den Iste, en ny Ægmasse dan- 

 nes og saaledes fremdeles. Antallet af paa liinan- 

 den følgende Hndskiftninger er derfor, iberegnet den, 

 der er gaaet umiddelbart forud for Iste postlarvale 

 Stadiiim, noiagtig det samme som Antallet af Væxt- 

 striber paa hver Valvel, og omtrent Ugemange 

 Grange har i Regelen Individet afsat en Ægmasse. 

 Efterhvert som Skallen paa denne Maade ved ny- 

 dannede periphere Lag tiltager i Størrelse, foran- 

 di-es lidt efter lidt dens Form, idet Rygkanten bli- 

 ver mere og mere bnet i sin foi^reste Del. Samtidigt 

 bliver de primære Valvler ligesom skudt fortil og 

 indtager tilsidst en forholdsvis liden Del af Skallen 

 ved dennes øverste forreste Hjørne, hvilket sidste i 

 samme Forhold bliver utA'deligere og mere afstumpet 

 (se Fig. 1). Hos meget gamle Individer antager 

 Skallen tilsidst, seet fra Siden, en næsten triangulær 

 Form, med den primære Area skudt helt fortil og 

 næsten umboformigt fremragende, saaledes som an- 

 tydet paa den af Prof. Lilljeborg givne Figur 

 (Skallen i naturlig Størrelse). 



Forekoinst og Leyevis. 



Allerede Grube har opgivet, at der i Berliner- 

 Museet findes opbevaret Exemplarer af denne Form, 

 indsamlede af H. Rathke i Norge. Men da dette 

 Fund ikke med et eneste Ord er omtalt i den sidst- 

 nævnte Forskers bekj endte Værk: «Beitrage zur 

 Fauna Norwegens», og jeg selv imder mine mange- 

 aarige Undersogelser af vor Ferskvandsfauna aldrig 

 havde paatriitfet den, fandt jeg Paalideligheden af 

 denne Opgift af Grube meget tvivlsom og udtalte 

 mig ogsaa derhen i en i Vid. Selsk. Forhandlinger 

 meddelt forelobig Meddelelse om Norges Ph^dlopoder. 

 Forst i Aaret 1885 lykkedes det mig med fuld Sik- 

 kerhed at faa constateret denne eiendommelige Phyl- 

 lopodes Forekomst her i Landet. Under en Reise, 

 jeg dette Aar foretog langs Sydky.sten af Landet, 

 tog jeg d. 22de Juli Station paa en ikke meget stor 

 og temmelig flad 0, «Mærdo», udenfor Arendal, og 

 fandt her allerede den forste Dag efter min Ankomst 

 store Mængder af Limnadia-Larver i et grundt med 

 Græsbund forsynet Tjern, «Storekjær» kaklet, be- 

 liggende omtrent midt paa Øen. Paa denne Tid var 

 kun meget faa Exemplarer naaet \\å over Larve- 

 tilstauden, men i Løbet af de følgende Dage op- 

 traadte postlarvale Stadier i stor Mængde, og ved 

 Skitten af Maaneden var ingen Larve længere at 

 iinde. Flere Exemplarer var da allerede ægbæ- 

 rende og havde Valvlerne forsynede med de forste 

 Væxtstriber. Ved min Afreise, d. 10de August, var 

 Skallen hos de største Individer omtrent 10 mm. 

 lang og havde 5 Par Væxtstriber. For om muligt 

 at finde fuldvoxne Individer, besogte jeg igjen Øen 



skin, out of the shell behind. After the exuviation 

 the valves acquire another line of growth outside 

 the first, a new mass of eggs is formed, and so on. 

 The number of successive exuviations, including 

 that which immediatelj' preceded the 1st post-larval 

 stage, is therefore exactly the same as the number 

 of lines of growth on each valve, and the animal 

 has, as a rule, depo.sited a mass of eggs about the 

 same number of times. AVhile the shell in this 

 manner increases in size by the addition of new 

 peripheral layers, it gradually changes its shape, 

 the dorsal edge becoming more and more curved in 

 its front part. At the same time the original valves 

 are as it were pressed forward, and at last occupy 

 a comparatively small part of the shell at its upper 

 front angle, which also, in the same jn'oportion, be- 

 comes more indistinct and blunter (see fig. 1). In 

 very old specimens the shell, seen from the side, at 

 last assumes an almost triangular shape, with the 

 original area pushed right to the front, and pro- 

 jecting almost umbonately, as indicated in the 

 figure given by Prof. Lilljeborg (the shell in its 

 natural size). 



Occurrence and Habits. 



Grube has already stated that in the Berlin 

 Museum there are preserved specimens of this form, 

 collected by A. Rathke in Norway. But as this 

 discovery is not so much as named in the latter 

 naturalist's well-known work «Beitrage zur Faiina 

 Norwegens», and I myself, during my man}' years' 

 investigations of our (Norwegian) fresh-water fauna, 

 had never met with the form, I considered the 

 ti'ustworthiness of Grubes statement to be very 

 doubtful, and expressed myself to tliat effect in a 

 preluninarv account of the Phyllopoda of Norway 

 in the Viden. Selsk. Forhandlinger (Proceedings of 

 the Scientific Society). Not until the year 1885 did 

 I succeed in siibstantiating with certainty the 

 occurrence of this peculiar Phyllopod in this country 

 (Norway). During a journey I made that year 

 along the south coast, I stopped, on the 22nd Jvily, 

 at a rather flat, and not very large island off Aren- 

 dal, called < Mærdo», and there found, on the very 

 day after my arrival, large numbers of Limnadia 

 larvæ in a shallow lake called «Storekjær», situated 

 in about the middle of the island, and with a grassy 

 bottom. At that time onlj' a very few specimens 

 were advanced beyond the larval condition, but in 

 the course of the few following days, post-larval 

 stages made their appearance in great numbers, and 

 by the end of the month there was not a larva to 

 be found. Several specimens were then already 

 carrying eggs, and had tlieir valves furnished with 

 the first lines of gi'owth. At the time of my 

 departure, the 10th August, the shells on the 



