chdi (Har.) Lagerh.: N. Atlanterhav, 60» N. br., 307,0 

 L. AV. (Haslum) med TJialassiosira-arter. 



UdhredeJse. Ishavet — JST. Atlanterliav. 



Rhizosolenia, Ehr. 



Rh. alata. Briglitw. (1858) T. V, fig. 8. Peragallo (1892) 



p. 115, T. V, fig. 11. 



var. truncata, u. var. T. IV, fig. G7, a—c. 



Adskiller sig fra hovedformen og fra var. gracinima, 

 Cl. ved en kortere kalyjjtra med kegleformet, ret, bred, 

 tvært afskaaren spids. Diameter 5 — 13 (/. 



ForeJcomsf. Nordhavs-expeditionens st. 296, 312 etc. 

 N. Atlaiiterhav mai 189G (B/e). 



TJilhredehe. Hovedarten i alle liave, var. truncata i 

 N. Atlant., var. g)-aciUiiiia Cl. i Østersoen — Xordsoen. 



Rh. semispina, Hensen (1887) p. 84, T. V, fig. 39. 



Fig. Schiitt (iSOlij p. '21, fig. !l. 



Diameter 4.5 — 12.5 /<. 



ForeJionist. Nordhavs-expeditionens st. 296, 297. 331, 

 Vestkysten juni-juli 1895 (Hjort), februar 1896 (Nord- 

 gaard), Drobak februar 1896, N. Atlaiiterhav mai 1896 

 (Bie). 



Udhredehe. N. Atlanterhav — V. Østersøen. 



Rh. styliformis, Biightw. (1858) T. V. fig. 5. 

 (1892) p. 111, T. IV. fig. 1—5. 

 UdJjredelse. Atlanterhavet —Østersøen. 



Peragallo 



Chætoceros, Ehr. 



Arter af slegten Chætoceros forekommer til sine tider 

 i store mængder i havet ved vore kyster, hvor de ofte 

 danner hovedmassen af planktonet. Men det har hidtil 

 været forl)undet med vanskeliglicder at studere dem, da 

 ariernes systematiske forhold endnu ikkt' paa langt nær er 

 ndredede. Derfor har jeg fundet det heldigst lier at give 

 en samlet beskrivelse af alle de arter, som jeg har fundet 

 ved vore kyster. 



De ældre forskere, som har undersøgt diatomaceer, 

 har saagodtsom udelukkende undersøgt det glødede kisel- 

 panser enten tørt eller indesluttet i forskjelHge sterkt lys- 

 brydende medier; derved har man opnaaet at adskille fine 

 strukturforliold i cellevæggen. Disse methoder er vistnok 

 fremdeles nødvendige for alle diatomaceer; men for CJiæto- 

 ceros-arternc er de ikke tilstrækkelige. 



Fhæocgstis FoucJieti (Har.) Lagerh.; X. Atlantic Ocean, 

 66" N. Lat. 307,0 W. Long. (Haslum), with species of 

 TJialassiosira. 



D/strihution. Arctic Ocean, N. Atlantic Ocean. 



Rhizosolenia, Ehr. 



Rh. alata. Brightw. (1858j Pl. V, fig. 8. Peragallo (1892), 



p. 115, Pl. V, fig. 11. 



var. truncata, n. var. Pl. IV. fig. 67, « — e. 



Is distinguishable from tlie chief form, and from var. 

 gracinima, Cl. by a shorter calyptra, with a straight, broad, 

 abruptly-truncated point. Diameter 5 — 13 //. 



Occurrence. N. Atlantic Expedition Stations 29G, 312, 

 etc; N. Atlantic Ocean, May, 1896 (^Bié). 



Distrihution. Tlie chief species in all seas, var. trun- 

 cata, N. Atlantic, var. gracillima. CL, Baltic and North Sea. 



Rh. semispina, Hensen (1887) p. 84, Pl. V, fig. 39. 



Fig. Schiitt (180:5) p. 21, tig. 0. 



Diameter, 4.5 — 12.5 f^i. 



Occurrence. IST. Atlantic Expedition Stations 296, 

 297, 331; west coast of Norway, June and July, 1895, 

 (Hjort), February, 1896 (Nordgaard); Drøbak, February, 

 1896; N. Atlantic, May, 1896 (Bie). 



Distrihution. N. Atlantic, West Baltic. 



Rh. styliformis, Brightw. (1858) Pl. V, fig. 5. Peragallo 

 (1892) p. Ul. Pl. IV, figs. 1—5. 

 Distrihution. Atlantic. Baltic. 



Chætoceros, Ehr. 



Species of the genus Chætoceros occur at times in 

 great numbers in the sea round our (the Norw.) coasts, 

 where they often make up tlie great bulk of the plankton; 

 but their study has hitherto been attended with difficulty, 

 as the systematic conditioiis of the species are still far 

 from being made clear. I have therefore thought it best 

 to give here a coUective description of all the species that 

 I have found on our (the Norw.) sliores. 



Earlier naturalists, who have studied Diatomaceæ, 

 have examined almost exclusively the siliceous cell walls 

 which reniain after exposure to the action of fire, either 

 dry, or enclosed in various strongly refractive media, and 

 have thereby succeeded in distinguishing delicate structural 

 conditions in the cell walls. These methods, it is true, 

 are still necessary for all Diatomaceæ, but are not suffi- 

 cient for the Chætoceros species. 



