DIMORPHOCOCCUS A. Braun 1855, p. 44 



Colony free-floating; cells arranged in groups of 4 on the branched 

 wall fragments of the previous generation, not inclosed in mucilage; 

 quartets of cells composed of 2 ovate or subcylindric and 2 reniform 

 or cordate individuals; 1 chloroplast, parietal, with 1 pyrenoid. 



Dimorphococcus lunatus A. Braun 1855, p. 44 

 PL 55, Fig. 8 

 Cells in groups of 4 on the ends of fine, branched threads com- 

 posed of the fragments of the mother cell wall, the 2 inner cells of 

 the quartet ovate or subcylindric, the 2 outer cells cordate; cells 

 4^15|U, in diameter, 10-25/x long; chloroplast 1, a parietal plate nearly 

 covering the entire cell wall in mature individuals. 



Common and widely distributed; especially in the plankton of 

 soft water lakes and acid bog ponds. Mich., Wis. 



ANKISTRODESMUS Corda 1838, p. 196 



Cells acicular, crescent-shaped, or narrowly fusiform; solitary or 

 clustered in fascicles, sometimes straight, usually curved, and often 

 twisted about one another; without a gelatinous envelope. Chloro- 

 plast a thin, parietal plate covering most of the cell wall; pyrenoid 

 present or absent. 



Members of this genus are frequently found in great abundance 

 in small pools, along with species of Scenedesmus, coloring the 

 water green. They are common pioneers in waterlily and other 

 artificial ponds and laboratory aquaria. Care is needed to distinguish 

 some species of Ankistrodesmus from the myxophycean genus 

 Dactylococcopsis. 



Key to the Species 



1. Cells sigmoid or spirally twisted, sometimes wound about one another 2 



1. Cells fusiform, straight or lunate, not twisted 3 



2. Cells slender and elongate, spirally twisted 



about one another, forming bundles A. spiralis 



2. Cells wider and stouter than above, sigmoid-arcuate, twisted 



at the apices only, not forming bundles — - A. convolutus 



3. Cells straight, or nearly so, broadly fusiform, solitary A. Braunii 



3. Cells narrower than above, curved or lunate, or if straight, 



ending in long needle points — 4 



4. Cells fusiform or lunate, straight, or curved, 



usually entangled or clustered A. falcatus 



4. Cells arcuate, dorsal walls straight from the midregion to the 



sharply pointed apices; cells always solitary.^ A. fractus 



[252] 



