PROTOCOCCACE^E. 43 



periphery irregularly tvvo-lobed, sinus narrow, lobes unequal, now 

 and then constricted at the base, produced into an obtuse, rather 

 thick horn ; central cells polygonal, repand in front. 



Rabh. Alg. iii. 77. 



Pediastrum ellipticum, Ralfs Desm. t. 31, f. 10 d. 



Pediastrum Boryanum, ft., Ralfs Ann. Nat. Hist. xiv. (1844) 

 f. 8. 



In standing water. 

 Braun suspects the verity of this species, which we have never seen. 



Plate XVII. fig. 2. a, 32-celled coenobium ; b, 16-celled coenobium X 

 400 diameters, after Ralfs ; c, marginal cells. 



Pediastrum gracile. Br. Unic. Alg. p. 93. 



Cells quaternate, closely joined in a circle, centre open, 

 rarely closed ; cells deeply two-lobed, lobes ovate, produced 

 into a long divergent, acuminate horn. 



Rabh. Alg. iii. 75. 



Pediastrum simplex, Ralfs Desm. t. 34, f. 15 a b. 



In pools. 



This appears to be a very rare species, at first referred to P. simplex 

 Meyen, from which it differs in the cells, being deeply two-lobed. 

 Plate XVII. fig. 3. 4-celled crenobia X 400 diameters, after Ralfs. 



Pediastrum pertusum. Kutz. Phy. Germ. p. 143. 



Ccenobium orbicular, pierced with lacunae, of variable size, 

 composed of as many as 64 cells ; cells of the periphery loosely 

 connected at the base, bilobed almost to the middle : lobes 

 straight, produced into a hyaline horn, sometimes acute, some- 

 times obtuse or truncate ; central cells more or less exactly 

 quadrangular, emarginate in front, even, with two paler spots. 



SIZE. Perfect cells '016--022 mm. transverse diam. 



Rabh. Alg. iii. 75. Ralfs Desm. t. 31 ? f. 6 a, b. Braun 

 Unicell. Alg. p. 92. 



Pediastrum Napoleonis, Ralfs Desm. t. 31, f. 7 c and e. 



Pediastrum selencea, Kutz., Pritch. Inf. t. 1, f. 53. 



In pools. 



Plate, XVII. fig. 4. a, b, c, 8-celled ccenobia ; d, 32-celled coenobium ; 

 e, 16-celled coenobium. 



var. &. clathratum. Br. Unicell. Alg. p. 93. 



Disc pierced with larger openings ; central cells deeply 

 notched and bilobate. 



Pediastrum cribriforme, Hassall Alg. t. 92, f. 4. 

 Plate XVII. fig. 5. 16-celled coenobium. 



var. c. brachylobum. Braun Unicell. Alg. p. 93. 



Cells larger, those of the periphery emarginate or trian- 

 gularly notched, shortly two-lobed ; horns very short, truncate, 



