Simplest Forms of Life. 307 



H. dissiiie/is, Breb. Cells 0.02-0.025 d., half as long. 



5. Gen. Diifymopriiim, Ktz. Cells short, cask-shaped, with oval 



section, both sides provided with two blunt teeth, in tubular 

 gelatinous envelope [sometimes absent]. Chlorophyll in a 

 cross, with starch granules. 

 D. Gretnllii, Ktz. Cells 0.05 d. ; half as long. 



6. (ien. Bambusina, Ktz. Cells short, barrel-shaped, circular in 



cross section, with two raised ridges in the middle which 



bear small teeth on two opposite points. Chlorophyll 5-6 



rayed. 



B. Brelnssonii, Ktz. Cells about 0.02 d., twice as long ; united 



into knotty, fragile filaments. 



7. Gen. Desmidium, Ag. Cells short, 3-4 cornered, deeply con- 



stricted in the middle (hence the corners appear bidentate). 



Chlorophyll rayed, directed towards the corners. In filaments, 



mostly twisted. 

 B). S7c>a>-tzii, Ag. Cells three-cornered, 0.02-0.04 d., half as 



long. Common. 

 D. quadrangiilare, Ktz. Four-cornered, rare. 



8. (ien. Micrasterias, Ag. Cells elliptic, flat, length and breadth 



about the same, divided by a deep median constriction into 

 two parts, each of which appears lipped, owing to another 

 more or less deej) constriction. Zygospores spinous. 



M. denticulata, Breb. Cells circular, 0.25 d. ; halves tri-labiate 

 the lateral lips deep, median lips again bi-labiate, lips all 

 emarginate with rounded corners. Common. 



M. rotata, Rlfs. Similar to the preceding, but middle lips curved, 

 with undulating borders ; smaller lips bent, with pointed 

 corners. Common. 



M. papi//ife>-a, Breb. Circular, 0.1-0.125 d., with glandulous 

 teeth. Halves five-lipped, middle lips bent ; curved. 



M. Crux Militensis, Ehr. Cells 0.01-0.125 d. ; halves three- 

 lipped ; smaller lips fissured ; bent. 



M. trinicaia, Breb. Cells 0.125 ^- Halves five-lipped, toothed. 

 The species of this genus, as of the following, are, in most 



cases, difficult to determine, because many transition-forms are 



found. 



9. Gen. Euastrum, Ehr. Cells elongate, 2-3 times so long as 



broad, deeply constricted in the middle ; halves lipped, or 

 only bent outwards ; zygospores verrucose. 



