. Synopsis of the naviculoid diatoms. Presented to the R. Swedish Academy of Sciences May 10, 1893. Diatoms. KONGL. SV. VET. AKADEMIENS HANDLINRAK. BAND 26. N:0 2. form of the objects, to which these forms are attached by the lower valve, and in Achnanthes there are several forms, which owing to other important characteristics must be placed in this genus, although they are not at all genuflexed. Moreover genuflexed species occur in groups of allied forms the greater number of which are straight, for instance in the Naviculee lineolatce, Nav. mi- crostigmaticcB, Gyrosigma, Pleurosigma, and in
. Synopsis of the naviculoid diatoms. Presented to the R. Swedish Academy of Sciences May 10, 1893. Diatoms. KONGL. SV. VET. AKADEMIENS HANDLINRAK. BAND 26. N:0 2. form of the objects, to which these forms are attached by the lower valve, and in Achnanthes there are several forms, which owing to other important characteristics must be placed in this genus, although they are not at all genuflexed. Moreover genuflexed species occur in groups of allied forms the greater number of which are straight, for instance in the Naviculee lineolatce, Nav. mi- crostigmaticcB, Gyrosigma, Pleurosigma, and in some species the degree of flexure seems to be subject to variation (for instance in Oyrosigma arcticum). The geniculated flexure is thus no generic cha- racteristic, though in most cases of specific value. Zone. The zone in the Eaphidieie is in most cases simple, that is without longitudinal di- visions, but in many AmpJiorce, in AmpMprora and in the group Libellus of the Naviculee microstig- maticm it is complex. This characteristic appears to be subject to very little variation and to be of importance in the limitation of genera. There are however in some cases small variations. The zone of Amphora commutata seems in some varieties to have, and in others not to have, faint divi- sions. Amphora rohusta has usually no divisions, but in a variety from California there are longi- tudinal rows of alveoli on the zone. In the Naviculee microstigmaticee also, some allied forms have divisions and others are without them. Still we may consider the complexity of the zone as an important characteristic. Outline of the valves. The outline of the valves of the naviculoid diatoms is very variable, presenting every intermediate passage from narrow linear to almost orbicular. The valves are non-constricted, constricted, or biconstricted, and, occasionally, some forms have 3 or 4 constrictions. Sometimes the valve is sigmoid. The following schematic figures will illustrate the meaning of the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectdiatoms, bookyear1894
