2. Melosireæ. 



Tliala8sio!!iii-a Cl. 

 T. Nordenskioldi ( l 



Occurs iu i;Teat quantities in April (fi-oni tlie end of Mai'ch ' 

 into the month of May) during the inflow of diatoms, both along i 

 the western and northern coasts. ' 



Distribution: Arctic and boreal species, occurs in the winter 

 tolerably far south along the Eui'opean coasts of the Atlantic and 

 its arms (at least as far as The English Channel). On the west 

 coast of Norway and at the Færoes in quantities in the months of 

 March — May, strangely enough in both localities in August with a 

 less marked secondary maximum. 



T. gravida Cl. 



(PI. VI, tig. 4). 



Like the preceding species in almost every respect. Occurs of- 

 ten together with it. Endocysts frequent in April. 



Distribution: On the whole the same as T. Nordenskioldi, but 

 perhaps less decidedly arctic. 



T. hyalina (Grun.) Gran. 

 (PI. VI, fl;^. 5). 



Gban L. 65, p. 4. 7. Clevei Gkan L. 64, p. 29, pi. 4, f. 

 60—62. C. hyalinus Grun. L. 48, p. 113, pi. 7, f. 128; L. 83, 

 pi. 3, f. 28. Vix CoscinodiscHs knjophilus Grun. L. 83. pi. 3, 

 f. 21. 



Gran remarks (L. 65 p. 4), that he had at first suspected his 

 new species, T. Clevei, to be identical with Grunow's Coscinodiscus 

 krijophlliis, but that he had not then seen the structure of the valve. 

 Later, by the help of material from the Karajak Fiord (Greenland) 

 he felt sure that the species were identical. As, however, Cleve 

 (cfr. Gran) calls attention to the identity of C. hyuUnus Grun. in 

 Arctic Diatoms (L. 48) with T. Clevei, Gran has altered the 

 name. 



That T halassiosira Clevei Gran and Coscinodiscus hyalinus 

 GiiuN. are identical, is quite certain. The only objection, which 

 might be made to this, was, that in Grunow's figure of Coscino- 

 discus hyalinus no asymmetrical marginal apiculus is to be seen. 

 By the kind permission of the Riksmusæum in Stockholm 1 have 

 been enabled to compare the slides (of mud from the Kara Sea) in 

 which Grunow found C. hyalinus, and I can affirm that there is 

 always a well marked asymmetrical marginal apiculus, larger than 

 the others. That this is not to be seen in Grunow's figure is 

 evidently (as is also the reason in the case of Porosira glacialis 

 and others) because it may so easily be mistaken for a foreign body 

 (dirt) which is only there as a matter of chance. (The preparations 

 referred to were, in fact, rather dirty.) 



The specimens of C. hyalinus from the ivara Sea altogether 

 plainly showed that this species is identical with tlu^ one which 

 occurs on the northern coasts of Norway in the Spring. 



On the contrary, it seems to me to be open to considerable 

 doubt as to whether C. hyalinus Grun. and C', kryophilus Grun. 

 are identical. It is quite strange that Grunow, in an exceedingly 

 careful and exact monograph on the family in question, should illu- 

 strate and mention these species as different ones without hinting at 

 any connection between them. Certainly he considered the asym- 

 metrical apiculus to be characteristic of the one species only, C. 



kryophilus: but thei'e is, nevertheless, a great ditt'ereuce in the fi- 

 gures, both with regard to structure and the marginal apiculi. 

 These latter are particulai-ly small in C. kryophilus, while in C. 

 hyalinus they are very plain and comparatively large. The struc- 

 ture too of C. kryophilus is considerably coarser than that of C. 

 hyalinus, even if one does not put too much weight on the fasci- 

 culi, which in the figure of C. kryophilus are very clear and regu- 

 lar, while in C. hyalinus they are indefinite. 



In material from Cape Wankarema (Vega Expedition) — ^hich 

 material was also kindly lent to me by the Riksmusæum, Stock- 

 holm — I really found a Coscinodiscus which seemed in every re- 

 spect to correspond to C. kryophilus. It had just that characteristic 

 form of the asymmetrical apiculus, which is figured by Grunow, 

 and also the very small marginal apiculi, which are much less 

 conspicuous in comparison to the asymmetrical apiculus than is the 

 case in C. hyalinus. (PI. YI, f. 6, a, b.) 



Distribution: On the arctic coasts of Greenland, Fi'anz Jo- 

 seph's Land and Jan Mayen. On the northern coasts of Norway, 

 here only observed during the time of the inflow of diatoms, when the 

 species occurs in large quantities. Towards the south, it has been 

 found at Ona in Romsdal (in the Spring, not rare; cfr. Gean L. 

 70, p. 170). 



Seems not to occur with us in the months of June — February. 

 If it does not then — as Gran supposes — „over-summer" at the 

 bottom by the help of resting spores, it must — if it is actually 

 found wanting in the other months of the year than just the Spring 

 ones — every year be brought in from outside. 



T. decipiens Grun. 



(PI. VI, fig-. 3). 



Coscinodiscus decipiens Grun. in Van Heurck L. 88, pi. 91, 



f. 10 (from Lamlash Bay). A. Schmidt L. 126, pi. 3, f. 38. 



Thalassiosira gelatinosa Hensen L. 87, p. 87. Orthoslra angulata 



Greg. L. 74, p. 498, pi. 10, f. 43 and 43 b. 



As it seems to me beyond doubt that Grunow's Cose, decipiens 

 is the same species a.s Hensen's Thalassiosira gelatinosa (as this 

 species is understood by Cleve and others), I have found it neces- 

 sary to alter the name, the more so as Hensen's description is very 

 incomplete. 



I 'have not had any opportunity of making comparisons with 

 Grunow's work (Algen und Diatoraaceen aus dem Kaspischen Meei'e 

 in Dr. O. Schneider: — Naturwiss. Beitr. z. Kenntniss d. Kaukasus- 

 lander, Dresden 1878); but as Grunow himself figures a specimen 

 from Lamlash Bay in Van Heurck's Synopsis, I have thought that 

 I could keep to this figure, which undoubtedly represents the 

 same species which Cleve, and others after him, has called T. 

 gelatinosa Hens. Grunow remarks that the species is identical with 

 Orthoslra angulata Greg. 



Gregory's description (L. 74, p. 498) does very well too for 

 our species, less the drawing. It is interesting that Gregory has 

 found the species occurring in chains. His opinion, viz. that these 

 chains are constructed similarly to those of Melosira (where the 

 links touch each other), may no doubt be accounted for by the fact 

 that the long marginal apiculi in a side view may so easily produce 

 the same image as the cells. 



In the plankton from the northern coasts of Norway, this spe- 

 cies appears to vary considerably. Two principal series of forms 

 occur, the one with numerous marginal spines and a not very plain 

 exeentric structure, but plain fasciculi; the other with fewer mar- 



