K0N6L. SV. VET. AKADEMIENS HANDLINGAR. BAND 27. N:0 3. 73 



I. Parallelistriatee, which comprises forms generally small, often with capitate or rostrate 

 ends, and with close, parallel or slightly radiate striae. The axial area is indistinct or very 

 narrow. 



Several of these forms resemble small fresh-water species of Caloneis, and it may be 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 striae of the Caloneis-forms, and which is indeed often seen in these only with great 

 difficulty. 



II. Capitatce. Small forms, with capitate or rostrate ends, radiate striae, and narrow or 

 indistinct axial area. 



III. Divergentes. Smaller or larger, linear, sublanceolate, or subelliptical forms, with 

 rounded ends and strongly radiate striae. The axial area, in some species narrow, is in others 

 moderately broad. From the smallest species of this group, P. JBrebissonii, to the large P. epis- 

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

 with P. microstauron of the Capitatae. Small forms of P. Brebissonii seem also to graduate into 

 the group of 



IV. Distantes, comprising lanceolate to elliptical, or elliptic-linear forms, remarkable for 

 their distant striae. 



V. TabellariecB, comprising forms generally linear, narrow, often gibbous in the middle 

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

 ends. The terminal fissures are more or less bayonet-shaped. The area is distinct but moderately 

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

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



VI. Brevistriatce, comprising linear forms, with very broad axial area and parallel striae. 

 In P. hemiptera this group touches the following. 



Vn. Major es, usually large, linear, and slender forms with parallel or radiate striae, 

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



Vni. Complexw, 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. groenlandica seem to point to an affinity with some 

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

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



Among the Naviculae are some forms, which, on account of their smooth striae might be 

 placed in Pinnularia, especially Navicula Yarrensis, typical specimens of which have some likeness 

 to P. alpina; but there is, I believe, no true relation between these forms, the terminal fissures 

 of P. alpina being spirally twisted and large, those of Nav. 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 N. elegans. These forms are 

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

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

 in Navicula than in Pinnularia. The small species Nav. hungarica and Nav. costulata with 

 coarse, apparently smooth, striae 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 Lineolatee, for in- 

 stance Nav. cincta. 



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



10 



