KONGL. RV. VET. AKADEMIENS HANDLINGAR. BAND 27. N:() 3. 73 



r. Parallelistriatce, which comprises forms generally small, often witli capitate or rosti-ato 

 ends, and with close, j)arallel or slightly radiate stria>. The axial area is indistiiKtt oi- very 

 narrow. 



Several of these forms resemble small fresh- water species of Caloneis, and it may Ije in 

 some cases questionable whether they should be classed with Pinnularia, or with the forms 

 of the Caloneis Silicula-type. The only distinction is the absence of the longitudinal line which 

 crosses the striic of the ('aloneis-forms, and wliich is indeed often seen in these only with great 

 difficulty. 



II. Ca2>if'(f<f. Small forms, witli capitate or rostrate ends, radiate stritc, and nai'row or 

 indistinct axial area. 



TIT. Dircrf/cntes. Smaller or larger, linear, sublanceolate, or subelliptical forms, with 

 rounded eiuls and strongly radiate strite. The axial aiea, in some species narrow, is in others 

 moderately broad. Fi'oni the smallest species of this group, P. Brehissonii, to the large P. epis- 

 copulis is a continual series of forms, while on the other side P. Brchissotiii is closely connected 

 with P. microsfanron of the Capitata;. Small forms of P. Brf'hissonii seem also to graduate into 

 the group of 



TV. Disf antes, comprising lanceolate to elliptical, or elliptic-linear forms, remarkable for 

 theii' distant striie. 



V. Tah('Ilaric<r, comprising forms generally linear, narrow, often gibbous in the middle 

 and at the ends. The stria; are usually strongly radiate in the middle, and convergent at the 

 ends. The terminal fissiires are more or less bayonet-shaped. The area is distinct but moderatel}^ 

 narrow. This group is closely connected with the divergentes, P. Legiimen being an intermediate 

 form. On the other hand it is also closely allied with the next. 



VT. Brevistriatcf, comprising linear forms, with very broad axial area and parallel striai. 

 In ]'. hemiptera this group touches the following. 



VII. Ma jo res, usually large, linear, and slender forms with parallel or radiate striai, 

 narrow area, oblique median line and comma-like, terminal fissures. 



VITI. Complexie, linear, usually large forms, remarkable for their complex median line. 



Several forms belonging to Pinnularia have .some apparent resemblance to those belonging 

 to Caloneis, but it is questionable whether they are really connected. The longitudinal struc- 

 tureless depression of P. Trevelyana and P. groenJandica seem to point to an affinity with some 

 species of Caloneis, which also have smooth striee, but the terminal fissures of the above named 

 species of Pinnularia are too peculiar to allow of their union. 



Among the Naviculte are some forms, which, on accoimt of their smooth strite might be 

 placed in Pinnularia, especially Naricula Yarrensis, typical specimens of Avhich have some likeness 

 to B. alj>ina; but thei'e is, I believe, no true relation between these forms, the terminal fissures 

 of P. alpina being spirally twisted and laige, those of Nar. Yarrensis being indistinct. 



Among the many fossil forms, recently discovered in Hungary and described by Dr. Pan- 

 TOCSEK, are several closely connected with N. Yarrensis and with A. eleyans. These forms are 

 also allied to the group of Nav. palpehralis. All these seem to be related to the groixp of Nav. 

 lineolata;, for which reason I consider it more natural to class Nav. Yarrensis and its allied forms 

 in Navicula than in Pinnularia. Tlie small species Nar. hmigarica and Nar. costvlata with 

 coarse, apparently smooth, strirf seem naturally to belong to the same group as Nav. Yarrensis, 

 although it may not be denied that they are also akin to some forms of the LincoJatce. for in- 

 stance Nav. rinefa. 



K. Sv. Vet. Akad. Handl. Band 27. N:o 3. 10 



