PROTOCOCCACE^E. 33 



a ccenobium. Propagation by division in the cells whence arise 

 gonidia, which unite themselves into a ccenobium within the 

 mother-cell, and are at length set free by the rupture of the 

 cell-membrane. 



GENUS 25. SCENEDESMUS. Meyen. (1829.) 



Cells polymorphous, equal or unequal at the ends, often pro- 

 duced into a spine-like horn. Frond or family composed of 

 from 2 to 8 oblong, fusiform, or elliptic cells, connected into a 

 single or double continuous row ; propagating by means of the 

 repeated segmentation, in parallel planes, in one or two direc- 

 tions, of each of the cell- contents into one or more brood families 

 (not motile), set free by the bursting of the parent-cell wall. 

 Ndgeli. 



A. Cells unarmed. 

 J Scenedesmus obtusus. Meyen. Rabh. Alg. in., 63. 



Cells oblong or ovate, obtuse at the poles, 4-6-8 loosely con- 

 nected in a simple series, or joined obliquely, 3-5 times as long 

 as broad. 



SIZE. Cells -0055--007 mm. diam. 



Ralfs Ann. Nat. Hist, xv., p. 404, t. 12, f. 8. Brit. Desm. 

 p. 193, t. 31, f. 16. Archer in Pritch. Infus. p. 753, t. 1, f. 

 37-39. Hass. Alg. p. 394, t. 92, f. 15. 



In boggy pools. 



This species appears to be much less common than 8. quadricauda, 

 from all forms of which it may be readily distinguished, not only by the 

 difference in the form of the cells and absence of spines, but the remote. 

 ness of one cell from its neighbour and their alternation. 



Plate XIII. Jig. 5. Cells in families of 4 and 8, magnified 400 

 diameters. 



Scenedesmus acutus. Meyen. Rabh. Alg. in., 63. 



Cells fusiform or ovate-fusiform, acute at each extremity, 

 2-4-6-8 united in a series, either single and straight, or double 

 and irregularly alternate ; 3-6 times as long as broad. 



SIZE. Cells -OOSS-'OOoS mm. diam. 



Ralfs Ann. Nat. Hist, xv., p. 404, t. 12, f. 6. Brit. Desm. 

 193, t. 31, f. 14. Hass. Alg. 393, t. 92, f. 14. 



In pools and boggy places. 



var. b. obliquus. Rabh. Alg. in., 63. 



Cells elliptic, fusiform, arranged in two generally oblique 

 series, the outer cell of each not in contact with any of those in 

 the other series. 



Scenedesmus obliquus, Ralfs Desm. p. 192, t. 31, f. 15. 

 English Botany, t. 2933. 



Scenedesmus triseriatus, Ralfs Ann. Nat. Hist, xv., p. 403, t. 

 19 f 7 



A.fJj JL i 4 * 



