CALOTRICJTEJS. 279 



of the two plants at other periods of the season. Other two lochs in the 

 vicinity did not contain the plants alluded to.'' 



As these pages are being printed (July, 1884,) this alga has been sent 

 ns from a large pond between Haslemere and Farnbam, rendering the 

 water quite opaque, described as " like a mixture of pea soup and 

 water." See also Bornet and Flahault, " Sur da determination des 

 Rivulaires, &c.," in "Bulletin de la Societe Botanique de France," 

 t. xxxi., p. 76 (1884). 



Plate CXlV.Jig. 2. a, natural size ; 6, cluster magnified ; c, trichomes- 

 X 400 diarn. 



Rivularia calcarea. Eng. Bot. 11. eel., t. 1799. 



Hemispherical, gregarious, confluent in a very hard mamil- 

 lose incrnsting blue-green or brownish stratum, internally re- 

 peatedly zoned, zones of a darker green, trichomes rather thick, 

 pale blue green, slightly flexuous, distinctly articulate, ending 

 at the apex in a colourless hyaline point ; sheaths narrow, 

 colourless or brownish at the base ; heterocysts globose, lower 

 joints of the trichomes equal in length to their diameter. 



SIZE. Trichomes *006 mm. diam. 



Eng. Fl. v., 392. Harv. Man. 150. 



Ainactis calcarea, Kutz. Tab. Phyc. ii., t. 63, f. 11. 



Lithonema calcarea, Hass. Alg. 265, t. 65, f. 2. 



Zonotrichia calcarea, Rabh. Alg. Eur. ii., 213. 



Linckia dura, a calcarea, Grey. Fl. Edin. 322. 



On rocks and stones in streams. 



Plate, CKVI. fig. 3. a, section natural size ; b, portion with trichomes 

 X 400 diam. 



Rivularia duxa. Kutz. 



About the size of a mustard seed, rather hard, dark bluish- 

 green, becoming brownish or brackish ; trichomes seruginous, 

 variable in the same thallus, some thin and inarticulate, others 

 thicker, articulate and torulose, all with distinct sheaths, 

 lengthened at the apex into a colourless flexuous inarticnlated 

 thread ; lower joints as long as broad, or nearly so, upper ones 

 longer, all granulated ; sheath colourless, or yellowish ; hetero- 

 cysts rounded, oblong. 



SIZE. Trichomes -OOS-'OOO mm. diam. at the base. 



Limnactis dura, Kutz. Tab. Phyc. ii., t. 64, f. 1. Rabh. Alg. 

 Eur. ii., 211. 



Rivularia radians, var. dura, Kirch. Alg. Schles. p. 223. 



Attached to aquatic plants, especially Chara. 



Plate C XV. fig. 2. a, natural size , b, section enlarged; c, trichomes 

 X 400 diam. 



