Marine Plankton from the East-Greenland Sea. 265 



Hyalodiscus Ehrbg., 1845. 

 9. Hyalodiscus laevis Ehrbg., Monatsber. Berlin. Akad. Wis- 

 sensch. 1845, p. 78; Cleve u. Grunow, K. Svenslia Vet. Alcad. Handl., 

 Bd. 17, No. 2, 1880, p. IKk Peragallo, Diatom marin, de France, pi. 119, 

 fig. 20; //. su&f///s Bailey, Smithson. (>ontril). to knowledge, vol.7, 1854, 

 p. 10, fig. 12; W. Hendry, Quart. Journ. Microsc. sc, 1861, p. 179; 

 C.leve u. Grunow, 1. c; Gran, Bibliotheca botanica, Heft 42, p. 5, pi. 1, 

 fig. 19; Peragallo, 1. c, pi. 119, fig. 7. Cfr. Stockmayer, Annal, k. k. 

 naturh. Hofmuseum, Wien, XXIII, 1909, p. 69. 



In some samples from Danmarks Havn I found sparingly a large 

 species (150-|-170/i in diameter of the valve) of Hyalodiscus which, 

 I think, is identical with Gran's H. siibtilis from Karajak Fjord. On 

 the other hand I cannot find any difference of valve between H. 

 lœvis Ehrbg. and//, siibtilis Bail. Already Hexdy (I.e.) has suggested 

 that the distinctive marks in the proportion between the entire valve 

 and the central part (umbilicus) as well as in the structure of the 

 ^^umbilicus" are value-less, and my here given figures (Fig. 1) which 



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 \ 



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Fig 1. Hyalodiscus laevis Ehrbg. 2.Î0 t. m. 



are chosen as extremes will, taken together with the figures by 

 Peragallo, show that these characters are subject to great variabi- 

 lity. Therefore, I find it necessary to unite the two species in one 

 to which //. scoticus (Kutz.) Grun. must be referred as a dwarfy 

 variety. — July — September. 



Distrib. Coast-species, not true i)lankton form, found scattered over 

 tlie eartli, especially in colder rej^ions; often found in fossil depots. 



Cosciiiqdisciis Ehrbg., 1838. 



10. Coscinodiscus centralis Ehrbg., Abhandl. Berl. Akad., 1838, 

 p. 129; Mikrogeologie, i)l. 18, fig. 39. pi. 22, fig. 1 ; Jørgensen, Bergens 

 Museums Skrifter, 1905, p. 93, pi. 6, fig. 1 ; Gran, Nord. Plankton XIX, 



