. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . ation, but he has most inaptly used two of H. L. Smiths divisional Classification 121 names in quite a different sense. As a classification it fails because of theadmittedly artificial group of the Cryptoraphidese. There are two classificatory schemes which have the advantage of beingmuch more natural than any of the others, and are therefore deservingof more special mention. These are the schemes of Schiitt (1896) andForti (1912). The classi
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . ation, but he has most inaptly used two of H. L. Smiths divisional Classification 121 names in quite a different sense. As a classification it fails because of theadmittedly artificial group of the Cryptoraphidese. There are two classificatory schemes which have the advantage of beingmuch more natural than any of the others, and are therefore deservingof more special mention. These are the schemes of Schiitt (1896) andForti (1912). The classification proposed by Schiitt (96) has been adopted with slightmodifications by most investigators of the biology and taxonomy of diatoms,and its great merit lies in the fact that all the principal groups are to a greatextent undoubtedly natural assemblages of forms. Its fundamental division,separating all those diatoms with a radial symmetry of the valves (CentricDiatoms) from those with zygomorphic or irregular valves in which thestructure is in relation to a longitudinal line (Pennate Diatoms), is sharpand distinctive. It is briefly as follows :. *$m Jre*A*Vx^ £1 ##: §P •» ,..•.•••„• Pp *&; fill 3|ft i| J :^i^ T§^| fir. ..•.•..-.* i%*n& - :. , r^ -••.•... • ». ^f. - . ! s Iff 5^ a^ vJL»arV_>, ^i B*«j?a t:% Fig. 86. Two centric diatoms. The left-hand figure is the valve view of Aulacodiscus multipedex,x 150 ; the right-hand figure is the valve view of Aulacodiscus Crux, x 120. A. Centricse. Valves with a concentric or radiating structure around a centralpoint ; without a raphe or pseudoraphe ; valve view circular, polygonal, or broadlyelliptical, rarely boat-shaped or irregular. a. Discoidex. Cells shortly cylindrical or disc-shaped, in valve view circular;hyaline or with radiating or areolated markings. Includes the subdivisionsCoscinodiscete, Actinodiscese, and Eupodiscese. b. Solenoidese. Cells elongate, cylindrical or compresse
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