Various species of recent Diatomaceæ, to illustrate the Fossil remains of this Tribe of Vegetables. _For detailed descriptions, see pages 87-100._ Figs. 1 to 5.--Various kinds of _Xanthidia_: figs. 2, 3, 4, found in a pond on Clapham Common, and fig. 1. living in a pond near Westpoint, United States. 1.--Xanthidium _furcatum_: 1/24 of a line in diameter. 2.-- --------- _hirsutum_: 1/36. 3.-- --------- _aculeatum_: 1/24. 4.-- --------- _fasciculatum_: 1/24. 5.-- -------------------- variety of the above. 2*.--Pyxidicula operculata; Carlsbad, Bohemia: 1/48 of a line in diameter. 6.--Bacillaria vulgaris. 1/36 of a line in diameter. Pond on Clapham Common. 7.--Cocconeis scutellum: from the Baltic: 1/24 of a line. 8.--Navicula viridis: 1/6 of a line. Ponds on Clapham Common. 9.--The same; a side view; showing the currents produced in the water by the animal when in locomotion. 10.--Gallionella lineata: 1/36 of a line. Ponds on Clapham Common. 11.--Gallionella moniliformis: 1/72 of a line. 12.--Synhedra ulna: 1/9 of a line: the point _a_, marks the pedicle of attachment. Ponds on Clapham and Wandsworth Commons. 13.--Podosphenia gracilis: 1/12 of a line; attached to a thread of _Calothria_ and having by self-division formed a radiating cluster. Common in the ditches communicating with the Thames in Battersea-fields. 14.--Navicula splendida: 1/12 of a line in diameter. 15.--Lateral view of the same. 16.--Eunotia turgida: 1/14 of a line; the empty shell, with sixty-five ribs, viewed laterally. 17.--A living group of the same: 1/20 of a line: a piece of _Conferva rivularis_, beset with these animalcules. The smaller species are _E. Westermanni_. [All the above organisms were figured and described by Ehrenberg as animals (_Polygastrica_), and are comprised in his family _Bacillaria_; they are now, however, regarded as unquestionably vegetable structures, belonging to the family of Algæ, termed _Diatomaceæ_.] [Illustration: _Pl. 5._ _J. Dinkel del. G. Scharf lithog._ _Printed by Hullmandel & Walton_] DESCRIPTION OF PLATE V. _Illustrative of the Structure of Fossil Vegetables._ Fig. 1.--Polished transverse section of silicified Monocotyledonous Wood, from Antigua; p. 185. 1_a_.--Magnified 20 times linear. 1_b_.--Magnified 75 times linear. 2_a_.--Transverse section of silicified Coniferous Wood (_Abies Benstedi_) from the Kentish Rag, near Maidstone (Iguanodon quarry), × 120 linear; p. 173. 2_b_.--Vertical or longitudinal section of the same, × 250 linear.