106 DESMIDS OF THE UNITED STATES. 



divided in the middle by a rounded notch into two lobules 

 with tridentate or spinous ends ; end lobe short, more or less 

 eniarginate, the two sides of the apex usually somewhat reflexed, 

 with a subacute or rounded notch between ; lateral margins 

 furnished with two or three horizontal spines. End, trans- 

 verse and side views I Plate LII, figs. 13, 14, 15), rectangular, 

 with broad, square, and more or less sinuate sides and ends ; 

 angles dentate. 



Diameter 45-50 //.; length 70-75 ju. 



Frequent in pond near Minneapolis, Minn.; rarer in New- 

 Jersey and Pennsylvania. 



E. elegans, Eg. Plate XXVII, figs. 10-16; 25, 26. 



( >blongj our .Hid one-half to two time- as long as wide ; cen- 

 tral constriction narrow linear ; semicells with sides somewhat 

 converging, with a constriction near the truncate, angular end, 

 and another, often very slight, between this and the base ; ends 

 divided bv a linear or acute angled notch ; side view oblong 

 elliptic, apices acute-conic ; end view oval with central 

 inflation. 



Diameter 18-36//. Common. 



E. ROSTRATl m. Ralfs. Plate X X Y 1 1 . figs. 8,9. 



Varies from the preceding in the protuberant, emarginate, 

 or angular end- having a prominent, horizontal spine on each 

 angle. 



E. spinosum, Ralfs. Plate XX Y 1 1, figs. 4-7, 17. 



Nearly allied to the two preceding, bul separated by the 



more decided lateral notch in the basal lobes forming two dis- 

 tinct lobule-, each furnished with, usually, two horizontal or 

 diverging spines. Somewhat larger. 



Diameter 3540 fi. 



E. simplex, Wolle. Plate XXVII, figs. 18-22. 



Another form nearly allied to the above three species or 

 varieties ; separated by the absence of the lower constriction of 

 the semicell. Size is variable, diameter 16-36 a. 



The preceding four forms are closely related, and may be 

 accounted mere varieties. They are frequent. Having tor 



