. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . hilling (Dinoflagellatae in Die Dcutaelil. Oaten-, u. dcr tichweiz,Jena, 1913) has replaced the names Gymnodiniaceaa and Peridiniacese by Kyrtodiniaceic and Krossodiniacese respectively. 62 Peridinieae no clue to the sutures. This has been still further emphasized by Kofoid(07 c), who states that the actual separation of the plates in situ is the onlysafe guide to an analysis of the thecal wall. The plates are often covered with
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . hilling (Dinoflagellatae in Die Dcutaelil. Oaten-, u. dcr tichweiz,Jena, 1913) has replaced the names Gymnodiniaceaa and Peridiniacese by Kyrtodiniaceic and Krossodiniacese respectively. 62 Peridinieae no clue to the sutures. This has been still further emphasized by Kofoid(07 c), who states that the actual separation of the plates in situ is the onlysafe guide to an analysis of the thecal wall. The plates are often covered with minute spines, or with a close networkof ridges giving them an areolated appearance. Both pores and poroidsoccur on the plates, only the former being real perforations through the wing-like expansions which occur in some of the marine forms aresupported by variously arranged radial and transverse horns and ribs. Theseexpansions do not act merely as parachute-like structures : their dispositionis such that the sinking organism always assumes a definite position. Theexpansions of Ceratocorys, Phalocroma, Ornithocerctts, etc., and the apical. Fig. 44. Peridinium Willei , to show the plates composing the wall. A, ventralview; B, dorsal view; C, apical view; D, antapical view. 1—4, apical plates; 1—7,precingular plates; 1—3a, anterior intercalary plates; 1—5, postcingular plates;1 and 2, antapical plates. The sculpture of the plates is not shown in the figures,x 500. and antapical horns of Ceratium, are always asymmetrically disposed. Insome species Kofoid (10) has demonstrated that in the passive sinking of theorganisms, this fundamental asymmetry of horns and expansions causesthe body of the cell to turn on to its ventral face with the maximumexposure of body and horns to the direction of sinking, thus delaying thedescent. The sutures of the plates are sometimes scarcely visible, as in Peridiniumberolinense Lemm., but more often the lines of junct
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