No. 10.] FRESH-WATER ALGM. 35 



Selenastrum Reinsch. Cells lunate, attenuated on both 

 ends to a fine point, with firm, thin walls; arranged back to 

 back to form four- to eight-celled colonies. Multiplication by 

 autospores. 



S. acuminatum Lagerh., Fig. 46. 



S. sp. (?) (perhaps acuminatum), Fig. 43. 



Scenodesmus Meyen. Cells elliptical, cylindrical, oblong- 

 spherical, often drawn out into longer or shorter spines. One, 

 sometimes two, rows of cells are commonly joined laterally 

 into a ccenobium. Propagation by repeated division of the 

 cell contents into brood-families, which are set free by rupture 

 of the mother-cell wall. 



S. obtusus Meyen, Fig. 38. 



S. caudatus Corda, Fig. 36. 



S. caudatus var. abundans Kirch., Fig. 32. 



5\ caudatus var. typicus Kirch., Fig. 33. 



S. caudatus var. setosus Kirch., Fig. 34. 



S. acutus Meyen, Fig. 37. 



6". dimorphus Kiitz., Figs. 42, 44. 



S. antennatus Breb. var. rectus Wolle, Fig. 39. 



S.sp. (?), Fig. 35. 



Dimorphococcus A. Br. Cells united more or less in 

 fours on short branches ; the two intermediate, contiguous cells 

 oblique, obtuse-ovate; the two lateral, opposite and separate 

 from each other, lunate; families free-swimming, in irregular 

 clusters. 



Ankistrodesmus Corda (Rhaphidium Kiitz. ; Schroderia 

 Lemmermann). Finely granulate, cylindrical cells, usually 

 tapering at both ends and variously curved. The cells occur 

 singly, or gathered into groups, several radially joined, two 

 crossing each other, rarely two united at the end; covering 

 thin and smooth; division in only one direction. 



A. falcatus (Corda) Ralfs, Fig. 45. 



A falcatus var. acicularis West, Fig. 47. 



A. falcatus var. mirabilis West, Fig. 41. 



A. Braunii (Nag.) (?), Fig. 40. 



SUB-FAMILY V. CRUCIGENIE^. 



Cells gathered into flat coenobia. The cells are generally 

 rounded and sometimes furnished with spines. The groups of 



