134 FRESH-WATER BIOLOGY 



63 (64, 65) Transverse costae coarse, converging, projecting inward, often 

 with lines of dots between. . . Epithemia Brebisson. 



Fig. 104. Epithemia turgida KUtzing. 

 X 380. (Original.) 



64 (63, 65) Transverse stria tions punctate; end nodules present, but raphe 



wanting Eunotia Ehrenberg. 



Fig. 105. Eunotia pectinatis Dillwyn. X 625. (Original.) 



65 (631 64) Valves crescent-shaped, the raphe very near the concave margin, 



with end and middle nodules. . . . Ceratoneis Ehrenberg. 



There is but a single species. 



Fig. 106. Ceratoneis arcus Kiitzing. X 600. (Original.) 



Class II. Chlorophyceae 



Color, a chlorophyll-green. 



This group includes by far the greater number of forms of algae in fresh 

 water. It is so large and the characteristics of the different members so 

 varied that no characterization of the group as a whole wUl be attempted. 



1 (253) Plants fine, relatively small 2 



In regard to the Characeae the uncertainty of their nature and systematic position is fully 

 understood, but for convenience they will be considered at the end of the Chlorophyceae. 



2 (67) Plants of unbranched, septate filaments, shppery to the touch; or 



plants of single cells of two exactly symmetrical parts, some- 

 times imited into filaments. Chlorophyll in spiral bands, 

 central plates, or star-shaped bodies. 



Order Conjugales . . 3 



Filamentous or unicellular algae whose reproduction consists only in conjugation, that is 

 where the contents of two cells which are exactly alike, or at most differing only slightly in 

 reference to size, unite to form a single cell, the zygospore. 



Some authors would place the Bacillariaceae under this group on account of the union which 

 takes place before the formation of the spore, but as they differ in many respects from the dis- 

 tinctive members of this group they have been placed in a group by themselves. 



3 (59) Plants unicellular, occasionally united into filaments; cells constricted 



at the middle or not; one-half of each cell exactly symmet- 

 rical with the other half; 2, 4, or 8 individuals from a germi- 

 nating zygospore. . . Family Desmidiaceae . . 4 



The membrane mostly furnished with tiny protuberances and pores, both with a definite 

 arrangement; chromatophore radiating from or including one or more pyrenoids. Asexual 

 reproduction by the separation of the halves of the cell, between which two new halves are 

 formed, each attached to and identical with one of the older halves. In sexual reproduction 

 two cells come together, throw off their membranes, and their contents unite to form a 

 zygospore. This is usually furnished with conspicuous colorless spines. 



4 (22) Cells after division united into filaments 5 



