104 DESMIDS OF THE UNITED STATES. 



This plant bears some likeness to E. Nordstedtianum, but 

 is separated from it by the less prominent teeth, and especially 

 by the vertical position of the end lobules and the wide sinus 

 between them. 



E. divaricatim, Lund. Plate XXYI, figs. 18, 19. 



Cells one-fourth longer than broad, constriction deep, sinus 

 linear; semicells subtriangular, gradually narrowing from a 

 broad base to a truncate apex; sides undulate; polar lobe 

 short, not dilated, linearly notched; angles of the terminal 

 lobe, and of the basil lobe, armed each with a short aeuleus ; 

 vertical view elliptic, middle of each side granulate dentate, 

 ends also dentate. 



Diameter 32-36 a. ; length 40-45 u. 



Occasional in ponds, Pennsylvania and New Jersey. 



E. PokornyanuMj Gran. Plate XXXII, figs. 33, 34, 35. 



Semicells trilobed ; basal lobe-, margins crenate or emar- 

 ginate; terminal lobe erect, subcuneate, truncate, incised; 

 membrane smooth. 



Diameter 17-20 u.\ length equal to two diameters. 



Rather common, often intermingled with the following 

 two forms which are so nearly allied, that it is almost im- 

 possible to separate them. 



E. EROSUM, Lund. 



Very near the preceding; in front view barely separable. 

 End lobe usually rather wider, and not so deeply incised; 

 notch obtuse-angled. End and lateral views somewhat quad- 

 rangular with ends imperfectly tricrenate. 



E. insilaim:, Witt. 



This form the author eives as a variety <>f' E. bincde. I 

 prefer it separated because the basal lobes are emarginate, cor- 

 responding with the preceding two. It is distinguished by a 

 greater breadth of the terminal lobe and the absence of an in- 

 cision or notch ; sometime- slightly sinuate. Size rather less. 



E. ixerme, Lund. Plate XXIX, figs. 6, 8; Plate XX VII, 

 figs. 30, 3< i. 

 Subelliptic ; semicells subtriangular, apex somewhat pro- 

 tracted, truncate, deeply incised, not dilated or dentate; sides 



