PROTOCOCCACES, 41 
not even yet closely connected together, but exhibit spaces between 
them, so that in this stage it resembles P. pertusum. Not until the 
second day do the cells become closely applied together; the horns ac- 
quire their proper shape and length at the same time. All the figures 
are magnified 400 diameters. 
The number of cells which enter into the composition of a single disc 
vary inthe same species, so that it cannot be accepted as a character. 
The arrangement and limit of species adopted are those proposed by 
Braun (“ Algarwm wnicellarum,” 1855). 
Plate XVI. figs. 1to7. Development of Pediastrum, after Braun; 8 
a, b, zoogonidia. 
Section 3. pracrinium. Braun. 
Cells of periphery emarginate.or bilobate, lobes entire. 
Pediastrum selenza. Kutz. Rabh. Alg. 11.73. 
Ccenobium orbicular, entire, formed of 8-16 (rarely 31) cells. 
Cells of periphery narrow, lunate, acutely lobed; cells of dise 
slightly excised, central one five-angled; substance firm, rather 
thick. 
Sizz.* Ccenobium -028-:085 mm. diam. 
Braun Unicell. Alg. p. 83. Ralfs Desm. t. 21, f. 5. 
Pediastrum Napoleonis, Ralfs Ann. N. Hist. xiv. (1844) t. 
12, f. 6. 
Pediastrum elegans, Hassall Alg. t. 86, f. 19. 
Pediastrum lunare, Hassall Alg. t. 92, f. 3. 
In bogs, moor pools, &e. 
Plate XVI. fig.9. 4, 8-celled ccenobium ; }, 16-celled coenobium X 
400 diameters ; c, marginal cell. 
Pediastrum angulosum, Zir. Rabh. Alg. 111. 73. 
Ccenobium orbicular, oblong, or subreniform, continuous, 
composed of 8-16-32-64 cells. Cells all even, angular, those 
of the periphery truncate at the base and dilated upwards, more 
or less deeply notched in the middle, the lobes obliquely trun- 
cate, outer angle very shortly apiculate, inner one ending in a 
short horn. Central cells 5-6 angled, slightly repand in front, 
marked with a small transverse oblong pallid spot. 
Size. Ccenobium °12 mm. diam.; cells -019 diam. 
Hass. Alg. t. 86, f. 14. Ralfs Desm. t. 31, f. 11 ad, 
Braun Unie. Alg. p. 84. 
Pediastrum Boryanum, Ralfs Ann. Nat. Hist. xiv. (1844) t. 
12, f. 7, upper. 
Pediastrum excavatum, Hassall Alg. t. 92, f. 6. 
In bogs. 
Plate XVI. fig. 10. a, marginal cells ; b, 16-celled ccenobium ; ¢, 8-celled 
ceenobium X 400 diameters. 
* The size must depend on the number of cells of which the ceenobium 
is composed ; hence throughout this genus the dimensions given must only * 
be accepted as approximate. 
