Diatoms. 



221 



duration and that thus fossil valves will enlarge the apparent area 

 of distribution of the still living species. 



Most of the species of this group 111 are probably recent 

 ones, a great number of them being observed alive on the west 

 coast near Bergen. 



Next to group 111 it is group V, which contains the greatest 

 number of species. Many of them have a predominating southern 

 distribution, but occur, more or less frequently, as far north as the 

 coasts of the North Sea. To this group belong the following (a few 

 of which might perhaps rightly be reckoned to another group): 



Coscinodiscus Rothii. 



Biddulphia pulchella (a broken 

 valve, Troniso, (Y.l. 



B. regina (only exceptionally found 

 as far north as Scotland). 



B. funis (once found in Spits- 

 bergen). 



B. alternans. 



B. punctata. 

 Synedra undulata. 

 S. Hennedyana. 

 Raphoneis nitida. 

 Dimeregramma minus. 

 D. fulvum. 

 Glyphodesmis distans. 

 Grammatophora serpentina. 

 Niteschia punctata. 



N. acuminata. 



X. bilobata. 



N. lanceolata (a). 



Campylodiscus eximius. 



Surirella fastuosa. 



Achnanthes longipes. 



Pleuroneis distans. 



P. britannica. 



DonJcinia recta. 



I'll urosigma rigidum. 



P. formosum. 



P. speciosum. 



P. balticum. 



Scoliotropis latestriatd. 



Caloneis eonsimilis. 



C. blanda. 

 C. musca. 



Stauroneis salina. 



Navicula moniliformis. 



X. latissima. 



X. compn ssicauda. 



X. superimposita. 



X. palpebralis a, var. Barclayana, 



var. angulosa. 

 X. prwtexta. 

 X. clavata. 

 X. forcipata var. 

 I innularia claviculus. 

 P. Trevelyana. 

 Diploneis coffeiformis. 

 D. lineata. 



/>. (contigua var.) eudoxia. 

 I), notabilis (var. expleta). 

 D. fitsca var. Gregorii. 

 />. major. 

 D. nitescens 

 />. sejuncta. 

 I>. didyma. 

 D. ckersonensis. 

 D. crabro et var. pandura. 

 Mastogloia apiculata. 

 Amphora proteus var. contigua. 

 A. macilenta. 

 A. costata. 

 A. In iiml is. 

 A. sulcata. 

 A. aluf<i. 

 A. obtusa. 

 A. spectabilis. 

 A. ocellata. 

 Epithemia musculus. 



Many of these species were for the firsl time described and 

 illustrated in the work by Gregory above mentioned. 



All these species have not previously been mentioned from 

 the arctic zone. To this group should properly also most of those 

 be reckoned which are previously known from the arctic zone, but 

 only from the coast of Nordland („Finmarken"). 



Less numerous are the species of a mere western European 

 distribution, group IV. Such species are. however, on the whole 

 not numerous. Here belong the following species: 

 Coscinodiscus apollinis var. (west C. Normanni, C. fasciculatus A. 

 coast of Norway). Schm. 



Actinocyclus crassus. 

 Actinoptychus splen lens. 

 Biddulphia turgida. 

 Synedra baculus. 

 Niteschia litorea. 

 X. mi ricit Inns i Spitsbergen ?i. 

 ( 'ampylodiscus parvulus. 

 Cocconeis lyra (west coast 



of 



/ 1, urosigma attenuatum (?). 

 ( 'aloneis liber. 

 Schizonema crucigerum (?). 

 Navicula northumbrica. 

 N. peregrina var. Jcefuringensis. 

 N.prossecta (west coast of Norway). 

 Diploneis hyperborea var. excisa 

 i\\ esl coast of Norway). 



Norwaj I. 



These species, the Brst and the last ones only excepted, are 

 common to Great Britain and Norway. 



A closely related group is group II. including species with a 

 predominating western area, though also occurring right up to the 

 arctic zone. These are the following: 



Navicula directa <t var. subtilis. 



X. fortis. 



N. distans. 



X palpebralis var. semiplena. 



X. pygmoia. 



Diploneis hyalina. 



Amphora Icevis. 



< 'oscinodiscus Kuteingii. 

 Hyalodiscus scoticus. 

 Biddulphia rhombus. 



B. Sun tin,. 



Niteschia apiculata. 

 ( 'ampylodiscus angularis. 

 Rhoicosigma arcticum. 

 ('ah, tins brevis. 



The genuine arctic species, belonging to group I, are lew 



Coscinodiscus borealis. Niteschia Mitchelliana. 



Actinocyclus alienus? Gomphonema Icamtschaticum. 



Biddulphia arctica. Amphora groenlandica. 



Synedra Icamtschaticum. Diploneis entomon (A. p. p. 



S. rostellata. 1>. subcincta var. media). 

 Grammatophora arctica. 



All these species, except the last one, are besides very rare. 



At last we have the remarkable group VI of only southern 

 forms, partly only known from regions situated far to the south or 

 even only from the tropical zone. Their distribution (as earlier 

 known) extends northwards only as far as to the Mediterranean. 

 To this group belong: 



< 



(Coscinodiscus leptopus mus). 

 C. nodulifer. 

 Aulacodiscus Kittoni. 



A. Johnsonianus. 

 Biddulphia regina var. 



B. lata. 



Niteschia (insignis var.) spatku- 



lifera 

 X. coarctata. 



X. (Smithii var.) notabilis. 

 Amphora Grmffii. 



There may, however, be some doubt as to whether the forms 

 observed of Biddulphia lulu and Amphora Grwffii are identical with 

 those, which usually occur in southern regions. Moreover, Coscino- 

 discus leptopus, Niteschia spathulifera, X. coarctata, X. notabilis and 

 Biddulphia regina var. are all very rare and scarce. There remain. 

 however, Coscinodiscus nodulifer and the two species of Aulacodiscus, 

 all of which occur in comparatively lame numbers, and in several 

 samples. These species are easily recognizable, and have a pro- 

 nounced tropical area of distribution. 



Probably these species are all fossil, but I cannot at present with 

 certainty decide this. Coscinodiscus nodulifer has most probably 

 occurred as a plankton species. 



All the species of groups IV. V and VI, a considerable number 

 of species in all, have not before been known from the arctic zone. 



