ProtUtplankton. 



105 



13. Achn.nitlicæ. 

 AcliiiHiitlieM I' 



Wrongly entered in tlie tables as .1. Urniat^t Gkin. 



.1. tæniiita (Jkax L. i;:,, p. >). pi. 1, f. 10?, non (Juis. [.. 4S, 

 p. 22, pi. 1, f. 5. 



In long, very compact chains, which strongly remind one of 

 Fi-agUaria oceanica and also show a similar comparatively coarse 

 striation in side view. 



I have only once succeeded in seeing the valve from above, 

 and then it was very evident that the species must be another than 

 (iRUNow's, the distinct striation being also a proof of this. 



A. tæniafa in the various publications on plankton seem to be 

 ditferent species, and one of them is probably the same as the one 

 I have found. As I have not clearly seen the otiicr valve, 1 will 

 not venture to settle the species more definitely. 



The genuine Achnanthes tceiiiata Grun. is, however, ([uite 

 another species. By the kindness of the Riksmuseum in Stock- 

 holm. I have been enabled to examine the original preparations of 

 bottom mud from the Kara Sea (cfr. Gruxow 1. c). I have also 

 had an opportunity of finding the species in some of the mud 

 collected, and in this way I have become convinced that the spe- 

 cies really does — as mentioned by Clevk — form long, compact 

 chains (PL VIII, fig. 27). 



Grunow's illustration, which is very correct, very considerably 

 resembles Navicida Vanhoffeni Gran. 



There are, doubtless, here very closely related species, but they 

 form probably two, perhaps even three, quite distinct series. In 

 this case, as so often, a remarkably large quantity of species is found 

 in the arctic diatom plankton. 



There are at least here four Achmoithes species wliich must 

 be kept distinct. Fh'st we have Grunow's Achnanthes tceniatu, 

 which is comparatively thick-walled and strongly siliceous, and can 

 therefore, hardly be the same as that which Oestrup mentions and 

 illustrates (L. 139, pi. 2, f. 15) his being exceedingly thin-walled. Then 

 we have the closely allied species A. (tæniata var.?) hyperborea 

 Grcn. L. 83, p. 50, pi. 1, f. 4, 5. As far as I can see, this is 

 the same species as I have illustrated pi. VIII, f. 28, from 71" 

 48' n. lat., 49" 38' e. long. "'A 1900 (Barents Sea, S S Ilcimtlal, 

 a sample kindly given me by Dr. Gran). 



To these must be added the form which I have found in our 

 northern coast plankton and Oestrcp's from Greenland. 



Rather rare, but occurs in very long chains, only found durinir 

 the inflow of diatoms in spring. 



JJistribution: A. tæniata is an arctic, neritic species (Green- 

 land, Spitzbergen and Kara Sea), which also appears to occur 

 occasionally in large numbers in the Baltic Sea. 



14. Naviciileæ. 



>'avii'iila KoKY. 



A', directa K.m.ks. 



A. ScHM. L. 128, pi. 47, f. 1—."). 



Rather frequent durint;- tJie inflow of diatoms in spring; 

 but seldom occurs in any (luantity. Is most likely a genuine plank- 

 ton form. 



Distribution: Widely distributed in various forms on the coasts 

 of tiie Atlantic, right up to the arctic region.s. Also on the west 

 coa.st of Norway (spring, I'.iou). 



N. karianit (!hln. 



(IM. VII. tit'. '■i\). 



Ci-. and (iRiN. L. 4s. p. .{'J, pi. 2, f. 44. 



Under this name, a .species is entered in the tables which 

 occurred fre([uently both in 1H99 and 1900, but only at the time 

 of tiie inflow of diatoms, and seldom numerous. 



It is very thin walled, and most likely is a genuine plankton 

 form. It has the usual two chromatophores, one on each side (jf 

 the connective zone, .symmetrically situated. 



This form does not, however, answer well to the |trincipal 

 species and the illustiation referred to, but very much better to 

 N. frigida Grun. L. 83, p. 51, pi. 1, f. 25, which Cleve (L. 25) 

 considers to be a variety of X. kaiiana. 



The form which I have observed is, at any rate, closely allied 

 to N. kariana. The same form occurred in the sample before 

 mentioned from Barents Sea, S/S Heimdal, 1900, (cfr. under follow- 

 ing species) in which the more thick-walled forms answered very 

 exactly to N. frigida. Such a form is illustrated in pi. \'ll, 

 fig. 21. 



Distribution: N. kariana seems to be an arctic, and boreal 

 neritic form, which also occurs in the North Atlantic. It is known 

 fiom Greenland, Jan Mayen and the Kara Sea. The same form, 

 which was found in the plankton from the northern coasts, also 

 occurred in the spring 1900 on the west coast of Norway. 



I have a few times noticed delicate chains of a diatom which 

 is probably a Navicula, and very likely the species .just mentioned 

 (N. frigida). The chains were much twisted. (Fl. VII, fig. 21 f).. 



N. Vanhoffeni (iRA>. 

 (IM. VII, ti'r. 22). 



N. septentrionalis Cl. L. 40, non Oestb. 



Frequent during the inflow of diatoms in spring, occasionally 

 in large numbers. Otherwise absent. 



I should think it rather certain that this species is not a 

 genuine Naiicula. As I cannot, however, at present find any better 

 place for it, I have entered it under its usual name. In the tables, 

 I tried at first to distinguish between N. feptentriounlis and N. 

 Vanhoffeni, as these are ordinarily understood, but I had to give 

 it up later, and this is the case in the tables for 1900. 



At any rate, there is only one species in the plankton under 

 consideration. It is narrow boatsliapcd ; but as the connective 

 zone is very slightly siliceous, it does not stand being treated with 

 acids (but very well being ignited on cover-glass) and it is, there- 

 fore, very difficult to get a valvar view of it. 



As Gran (1. c.) mentions two species and under A', septentrio- 

 nalis remarks that it may easily be recognized in side view by 

 the plain stauros, it seems to me that the central nodule here sug- 

 gests the possibility of a stauros, which perhaps does not exist. 

 Gkan does not illustrate any central nodule in side view in his 

 figures of N. Vanhoffeni (f. 32 b). This nodule is, however, plainly 

 to be seen on specimens in my material, which in every respect 

 (when seen as chains) answer so remarkably well to N. Vanhoffeni 

 that I have not the least doubt that they really belong to this 

 species. With regard to the spaces between the links of the 

 chains, tliey are, to be sure, most often seen in specimens, pro ■■ • 



14 



