Myxophyceae 253 



2 Filaments coalesced into a crustaceous, spherical or hemispherical, 

 mucous or gelatinous plant mass or colony 

 (i) Heterocysts basal 

 A Filaments simple, parallel, associated in a crustaceous layer 



Isactis 

 B Filaments branched, radially arranged, associated in a spherical 

 or hemispherical colony Rivularia 



(2) Heterocysts intercalary Brachytrichia 



Genus AMPHITHRIX Kuetzing. Phyc. Gen. 220. 1843. 



Plant mass crustaceous or caespitose, thin, expanded, of a purple 

 or violet color, consisting of two layers: the lower layer composed of 

 densely interwoven filaments or of minute, radiately disposed series of 

 cells; the upper layer consisting of simple erect filaments, closely packed 

 together and tapering to fine points; sheaths thin, close, continuous; 

 hormogones solitary or in series; heterocysts not present. 



460. Amphithrix janthina (Montagne) Bornet and Flahault. Revis. des 

 Nostoc. Ann. Sci. Nat. Bot. VII. 3: 344- 1886. De Toni. Syll. 

 Algar. s: 601. 1907. 

 Collins. Notes on New England Marine Algae.— VI. Bull. Torr. Bot. 



Club. 23:2. 1896; Preliminary Lists of New England Plants. — ^V. Marine 



Algae, Rhodora. 2:41. 1900; Phycological Notes of the late Isaac Holden. 



— II. Rhodora. 7: 237. 1905. 



Plate XVI. fig. 3. 



Plant mass crustaceous, thin, purple; filaments i.S-2.2 mic. in diameter, 

 3-5 decimill. in length, erect, close, purplish; sheaths thin, uniform, very 

 close; cells equal to the diameter in length; hormogones 20 mic. in length; 

 cell contents pale blue-green. 



Massachusetts. On wet cliffs just above high water mark. Rockport. 

 (Collins). Connecticut. Coating stones in Island Brook, below R. R. 

 October. (Holden). 



Var. torulosa (Grunow) Bornet and Flahault. I. c. 344. De Toni. 1. c. 

 601. 



Collins. Notes on New England Marine Algae. VI. Bull. Torr. Bot. 

 Club. 23: 2. i8g6. Collins, Holden and Setchell. Phyc. Bor.-Am. Fasc. 

 6.' no. 262. 1897. Collins. Preliminary Lists of New England Plants. — ^V. 

 Marine Algae. Rhodora. 2:41. 1900. 



Filaments up to 5 mm. in length; trichomes torulose. 



Massachusetts. Forming a purplish coating on stone in ditch in salt 

 marsh near Linden Station, Revere. September 1892. (Collins). 



461. Amphithrix violacea (Kuetzing) Bornet and Flahault. Revis. des 

 Nostoc. Ann. Sci. Nat. Bot. VII. 3:344- 1886. De Toni. Syll. 

 Algar. 5:602. 1907. 



