374 DESCRIPTION OF [Polygastrica. 



merely an incrustation, such as will form on well-known Conferva, 

 placed under like circumstances, i. e. in water holding salts of iron 

 in solution, which are subsequently precipitated by exposure to the 

 air, and converted into the red oxide. 



The same author differs from Ehrenberg, as to the part played by 

 the so-called Gallmiella ferruginea in the production of the oxide of 

 iron in chalybeate waters, of bog-iron ore, of clay-iron ochi-e, &c. 

 For he observes, in many springs rich in h'on, no such orga- 

 nism is fotmd, although other Conferva may be present. Conferva, 

 however, not peculiar to such habitats, but common in springs and 

 ponds generally. 



Mr. Ealfs (Op. Cit. p. 352), however, in part supports Ehrenberg, 

 declaring, that though identical with Conferva ochraeea (Dillw}Ti) yet 

 "Ehrenberg is no doubt correct, in placing the plant in this genus, 

 as the filaments are siliceous and cylindrical." 



Gallionelia midulata = G. vcvrians (Hesse.) — Joints large, often 

 wider than deep, surface smooth ; the wall of the testules flexuose 

 beneath the integuments ; joints on the side, very finely radiate. 

 Diameter l-57Gth. 



G. coardata. — Joints smooth ; its habit is that of G. varians, but 

 it is devoid of the strias on the sides. (P. 14, f. 20 and 27.) 



G. grunidata. — The entii-e sxuface covered by dotted transverse 

 lines ; when concatenated, these lines arc longitudinal with reference 

 to the entire chain ; dotted longitudinal lines in the joints (transverse 

 in the chain) characterize G. marcliica, 



G. lirata. — Has the habit of G. granulata, but with stronger lines, 

 disposed like the strings of a lyre. United States. 



G. ocidas. — Habit of G. sol, but larger with equal and stronger 

 rays, sixty-seven in number, in the circuit of the very smooth disc. 

 Diameter 1 -240th. Southern Ocean. 



G. pileata. — '5 omi^ wider than deep, surface smooth; the two 

 sutures of the valves much separated, very minutely dotted ; lateral 

 disc convex, smooth, often narrower than the connecting band 

 (cingulum) or medium-body, hence the hat-like form. Diameter 

 1-64 8th. Southern Ocean. 



G. Sol. — Joints narrow, mostly five times deeper than broad, 

 nummiform ; disc level, large, smooth ; margin strongly and broadly 



