K0N6L. SV. VET. AKADEMIENS HANDLINGAR. BAND 27. N:0 3. 7S 



I. Parallelistriatce, wMch comprises forms generally small, often Avith capitate or rostrate 

 ends, and with close, parallel or slightly radiate striee. The axial area is indistiiiet or very 

 iiarrow. 



Several of these forms resemble small fresli-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 

 erosses the strise of the Caloneis-forms, and which is indeed often seen in these only with great 

 difRculty. 



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

 indistinct axial area. 



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

 roiinded ends and strongly radiate strise. The axial area, in some species narrow, is in others 

 moderately broad. From the smallest species of this group, P. Ijrébissonii, to the large P. ejji-s- 

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

 with P. microsfauron of the Capitatse. Small forms of P. Brébissonii seem also to graduate into 

 the group of 



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

 their distant strise. 



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

 and at the ends. The strise 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 gronp 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 strise. 

 In P. hemiptera this group touches the foUowing. 



Vn. Majores, usually large, linear, and slender forms with parallel or radiate strise, 

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



Vm. Complexce, linear, usually large forms, remarkable for their complex median line. 



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

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

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

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

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



Among the Naviculse are some forms, which, on account of their smooth stvise 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 Nar. Yarrensis being indistinct. 



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

 TOCSEK, are several closely connected with K. Yarrensis and with N. elegans. These forms are 

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

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

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

 eoarse, apparently smooth, strise 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 Lineolatce, for in- 

 stance Nav. cincta. 



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



