288 Minnesota Algae 



524. Rivvilaria borealis P. Richter. Siisswasseralgen aus dem Umanak- 



distrikt. Bib. Bot. 7: Heft. 42. 4. f. i. 1897. De Toni. Syll. Algar. 

 5: 664. 1907. 



Plate XX. fig. 7, 8. 



Colonies up to .5 mm. in diameter, small, spherical or hemispherical, 

 gregarious, sometimes confluent into an indefinite mass, soft, not indurated 

 with calcium carbonate; filaments up to 200 mic. in length, loosely asso- 

 ciated; sheaths in the interior of the mass close, those near the periphery 

 expanded, narrow at the apex, diffluent with age; trichomes 4 mic. in di- 

 ameter, ending in a hair; lower cells depressed, shorter than the diameter, 

 upper cells quadrate; heterocysts 4 mic. in diameter, spherical. 



Greenland. On submerged plants and especially on Myriophyllum 

 epiphytic a, in a lake. Umanak. (Vanhoflfen). 



525. Rivularia compacta Collins in Collins, Holden and Setchell. Phyc. 



Bor.-Am. Fasc. 11. no. 508. 1898; Notes on Algae. — I. Rhodora. i: 

 10. 1899. 



Colonies spherical or somewhat spherical, firm, not encrusted with 

 lime, smooth, minute, seldom over 2 mm. in diameter, dark green or black- 

 ish; filaments 15-20 mic. in diameter, closely packed; sheaths more or less 

 expanded above, colorless or yellowish; trichomes 6-10 mic. in diameter, 

 constricted at joints, tapering gradually to a hair-like termination; cells 

 about as long as broad below, one-third to one-quarter as long above; 

 heterocysts basal, spherical or oblong. 



Massachusetts. On stones, shore of Spot Pond, Middlesex Fells. Sep- 

 tember 1890. (Collins). Connecticut. Norwich. (Setchell). 



This species "resembles R. m i n u t u 1 a (Kuetz.) Born. & Flah., but the 

 thalli are much firmer, and not at all encrusted with lime; the trichomes 

 are slenderer, and the filaments more densely packed. In some particulars 

 it agrees with the description of R. beccariana (De Not.) Born. & 

 Flah., Revis. des Nost., part 2, p. 56; but the latter has more slender trich- 

 omes, with longer articulations and much narrower sheaths."- — Collins. 



526. Rivularia minutula (Kuetzing) Bornet and Flahault. Revis. des Nos- 



toc. Ann. Sci. Nat. Bot. VII. 4: 348. 1886. De Toni. Syll. Algar. 5: 

 672. 1907. 



Wolle. Fresh-Water Algae. V. Bull. Torr. Bot. Club. 8: 38. 1881. (R. 

 radians minutula Kirchn.). Stalker. Report on the Waterville 

 Cattle Disease. Fourth Bien. Rep. Bd. Regents Univ. of Minn. Suppl. I. 

 Rep. Dept. Agric. Univ. of Minn. 105, 108. 1887. (Limnactis minutu- 

 la Kuetz.). Collins. Algae of Middlesex County. 13. 1888. (R. radians 

 Thur.). Richter in Kuntze. Revisio Generum Plantarum. Part III. II. 

 389. 1898. 



Plate XX. fig. 9. 



Colonies up to 8 mm. in diameter, spherical or hemispherical, some- 

 times confluent, soft or indurated with calcium carbonate, blue-green or 

 brownish; filaments loosely associated; sheaths 27 mic. in thickness, wide. 



