PROTOCOOOACE. 43 
periphery irregularly two-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, 8., Ralfs Ann. Nat. Hist. xiv. (1844) 
. 8. 
In standing water. 
Braun suspects the verity of this species, which we have never seen. 
Plate XVII. fig. 2. a, 32-celled coonobium ; b, 16-celled coonobium X 
400 diameters, after Ralfs; e, 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 along divergent, acuminate horn. 
Rabh. Alg. iii. 75, 
Pediastrum simplex, Ralfs Desm. t. 34, f. 15 a 0b. 
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 coonobia X 400 diameters, after Ralfs, 
Pediastrum pertusum. Kutz. Phy. Germ. p. 143. 
Ceenobium orbicular, pierced with lacune, 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. 
Sizz. Perfect cells ‘016-022 mm. transverse diam. 
Rabh. Alg. iii. 75. Ralfs Desm. t. 31, f. 6a, 5. Braun 
Unicell. Alg. p. 92. 
Pediastrum Napoleonis, Ralfs Desm. t. 31, f. 7 ¢ and e. 
Pediastrum selenea, Kutz., Pritch. Inf. t. 1, f. 53. 
In pools. 
Plate XVII. fig. 4. a, b, c, 8-celled coenobia; d, 32-celled coenobium § 
é, 16-celled ccenobium. 
var. 0. 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, 
