Grevillea . eries of peculiar stipules attachedto the underside of the stem. 24 CONSPECTUS OF DIATOMACE^ GENUS AMPHORA. Prof. H. L. Smith. We have just received a further instalment of Professor SmithsNew Conspectus,* in which he treats of the genus Amphora. Innone of the genera of Diatomacece is the structure of the frustulemore difficult to understand; owing to the unequal development ofthe cingulum or connecting zone, the two valves of the frustuleare always visible at the same time. Professor Smiths explana-tion will enable the student to comprehend the peculiar formationof the frustu
Grevillea . eries of peculiar stipules attachedto the underside of the stem. 24 CONSPECTUS OF DIATOMACE^ GENUS AMPHORA. Prof. H. L. Smith. We have just received a further instalment of Professor SmithsNew Conspectus,* in which he treats of the genus Amphora. Innone of the genera of Diatomacece is the structure of the frustulemore difficult to understand; owing to the unequal development ofthe cingulum or connecting zone, the two valves of the frustuleare always visible at the same time. Professor Smiths explana-tion will enable the student to comprehend the peculiar formationof the frustules of the species of this genus. Bearing in mind that all diatomaceae are built after the sametype, or are silicious boxes, as already indicated in thepreface to the Synopsis, a reference to the following diagramswill make the structure of Amphora plain. If we commence witha typical navicula form, as in figure 1, presented in side view, wehave the median line (raphe) dividing the valve Passing to figure 2, we have the typical Cymbella, the median linebeing nearer to one margin than the other, or dividing the valveunsymmetrically. The more convex margin is termed the dorsum,and the other the venter. Although these are objectionable terms,yet, as they have been extensively adopted, I shall continue to usethem. If we pass now to figure 3, we have a more decided depar-ture from the navicula, in the curved raphe, and the more or lesscurved ventral margin. Let us look at these frustules in frontview; a and b are the striated valves, with central nodule, whilethe dotted lines c d represent the lines of suture (in all thefigures the lines are dotted); fig. 5, the end view of the same frus-tule. While the valves, as seen in figures 4 and 5, are slightlyconvex, the sutural zone, or hyaline part, which has upon it thesutural lines, is of the same width at the two ends c and d, fig. 4, * Published in The Lens, No. 2, vol. 2. CONSPECTUS OF 25 and again
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