Читать книгу The Diatomaceæ of Philadelphia and Vicinity - Charles S. Boyer - Страница 14

Table of Contents

Valves without a dividing line or cleft; markings more or less radiate; transverse section of frustule circular, polygonal, or elliptical, sometimes irregular.

Divided into four groups:

1. Discoideæ.—Frustules (cells) discoid; valves without horns or elevations (sometimes with processes).

2. Solenoideæ.—Frustules with numerous girdle bands.

3. Biddulphioideæ.—Frustules box-like, i. e., with the longitudinal axis greater than in the Discoideæ. Valves with two or more angles, elevations or horns.

4. Rutilarioideæ.—Valves as if naviculoid, but with irregular or radial structure.

Groups 2 and 4 are not included in our description. No. 2 contains plankton genera only, while No. 4 consists of genera not yet found in this locality.