The Simplest Forms of Life. 309 



X. armatiim, Rlfs. With short, divided spines. 



13. (len. Staitrastriim, Meyen. Cells very deeply constricted; 

 halves seen from the side three-five cornered. Zygospores 

 spinous. Numerous species. 



S. fucigcrum, Breb. Cells 0.055 — 0.09 d., in lateral view three 

 or four cornered; corners produced into divided prongs. 

 S. aciileatiim similar, but with undivided spines. 



S. mi/fici/m, Breb. Cells 0.027 — °-035 d.; halves elliptic, in side 

 view three or four (seldom five) cornered; surface smooth. 

 S. orbicularc, similar but circular. 



S. dilatati/m, Ehr. Cells 0.022 — 0.04 d.; surface regularly punc- 

 tate, in section quadrangular. 



14. Gen. Closferiiim, Ntsch. Cells spindel-shaped or cylindrical, 



not externally constricted in the middle, generally curved, 



sickle-shaped. Chlorophyll in cross-section stellate, with 



starch grains; the rays, in side view, appear as longitudinal 



bands. Zygospores smooth. 

 C. -Diance, Ehr. Cells 0.14 — 0.2 1., in the middle 0.0186. . Much 



curved, half-moon shaped. 

 C. lii/mla, Ehr. 0.4 — 0.66 1., in the middle 0.07 — o.i d. Back 



greatly arched ; front nearly straight ; cell covering smooth ; 



zygospores spherical. 

 C. Ehrenbergii, Mengh. Similar to C. lunula, but front surface 



turgid in the middle. Very common. 

 C. lineati/m, Ehr. Cells 0.5 — 0.66 1., about 0.03 d. in the middle, 



greatly attenuated at the ends : finely striped. 

 C. rostratum, Ehr. Cells 0.3 — 0.5 1., very slender, ends almost 



bristle-like, slightly bent. Closely striped and ribbed; spores 



four-cornered. 



15. (ien. Pc Ilium, Breb. Cells spindle-shaped or cylindrical, 

 straight, ends rounded. Chlorophyll as in Closterium. Spores 

 smooth. 



P. lamellosum, Breb. Cells o.i — 0.33 1., elliptic, slim ; ends 



rounded. 

 P. interruptum, Breb. Ends keel-shaped, attenuate. 

 P. margaritaceum, Breb. With verrucose, longitudinal bands. 



16. Cien. SpirotcBnia, Breb. Cells cylindrical or spindle-shaped, 

 with spiral bands of chlorophyll lining the walls. 



■Sp. condetisata, Breb. Cells 0.1 — 0.125 !•' °-°2 — 0.024 d., cylin- 

 drical, rounded on the ends, with one band of chlorophyll ; 

 generally in gelatinous sheath. 



