84 AQUATIC MICROSCOPY FOR BEGINNERS. 



on each semi-cell, not divided 'nor toothed, but 

 often curved; tubercle a curved row of bead-like 

 elevations. X. antilopeeum, Fig. 56, 

 14. Arthrodesmus (Figs. 57, 58). 



1. Spines on the same side curving or spreading from 



each other; surface smooth. A. incus, Fig. 57. 



2. Spines on the same side curving toward each other; 



surface smooth. A. conv&gens, Fig. 58. 



Fig. 58. — Arthrodesmus conv^rgens. Fig, 59. — Spirotaenia condensata. 



15. SpiroT/«nia. 



Ends rounded; spiral band closely wound. S. con- 

 densata, Fig. 59. 



16. Triploceras. 



Surface roughened by small projections arranged in 

 rows around the cell, their tips notched or finely 

 toothed ; cell from twelve to twenty times as long as 

 broad. T. verticilldtum, Fig. 60. This is classed by 

 the authorities on the subject, in thegen us Docidium, 

 and is therefore called Docidium verticillatum. 



Fig, 60, — Triploceras verticilldtum, 

 17. PfiNIUM. 



Cylindrical; ends rounded, surface smooth. P. 

 Brebissonii, Fig. 61. 



If it is desired to preserve any of the desmids or 



