44 COCCOPHYCE^E. 



or almost obsolete ; cells of the disc perforated 'with smaller 

 openings. 



Pediastrum tricyclum, Hassall Alg. t. 92, f. 1. 



Pediastrum Napoleonis, Hassall Alg. t. 92, f. 10. (?) 



Plate XVII. fig. 6. a, 5-celled coenobium ; b, 16-celled coenobium, fig. 

 4 ; /, marginal cell. 



SECTION 4. TETEACTINIUM. Braun. 



Cells of periphery emarginate or bilobate ; lobes emargi- 

 nate, bidentate, or bifid. 



Pediastrum Ehrenbergii, Br. EabTi. Alg. III., 72. 



Ccenobium orbicular or oblong, perfectly closed, composed of 

 8-16 cells, or quadrate, of 4 cells, which are wedge-shaped, 

 deeply lobed and arranged in the form of a cross ; cells of the 

 periphery cuneate, truncate at the base, deeply bilobate; sinus 

 narrow, lobes obliquely truncate, more or less notched, interior 

 angles twice as long, all acute, or shortly appendiculate ; central 

 cells yellow green, polygonal, one side repand or deeply notched. 



Pritch. Infus. t. 1, f. 52. 



Pediastrum tetras, Ralfs Desm. t. 31, f. 1. Ralfs Ann. Nat. 

 Hist. xiv. (1844) t. 12, f. 4. Hassall Alg. t. 86, f. 17. 



Pediastrum heptactis, Ralfs Ann. Nat. Hist. xiv. (1844) t. 

 12, f. 5. Ralfs Desm. t. 31, f. 2. 



Pediastrum simplex, Hassall Alg. t. 8, f. 17. 



Pediastrum biradiatum, Ralfs Desni. t. 31, f. 3, 4. 



In pools and boggy places. Not uncommon. 



Very variable in size. The 4-celled ccenobia are often to be met 

 with, mixed with Desmids and other Algae. 



Plate XVII. fig. 1. a, four-celled coenobia; &, 8-celled coenobia ; c, 

 8-celled ccenobium of unusual form, after Ralfs. 



var. a. txuncatum. Braun Utticell. Alg. p. 97. 



Lobes truncate. 



Pediastrum biradiatum, Ralfs Desm. t. 31, f. 4. 

 Plate XVIII. fig. 1. b, 8-celled caenobia. 



var. b. excisum. Braun Unicell. Alg. p. 97. 



Lobes slightly notched, emarginate. 



Plate XVIII. fig. 1. d, 4-celled coenobium ; e, 8-celled coenobium; 

 i, Ic, .16-celled coenobia. 



var. c. cuspidatum. Braun Unicell. Alg. p. 97. 



Lobes deeply notched, evidently bidentate or bicuspidate. 

 Pediastrum biradiatum, Ralfs Desm. t. 31, f. 3. 



In stagnant water, throughout Europe generally. 

 Plate XVIII. fig. 1. g, h, crenobia; /, marginal cell. 



