1 Hi DESMIDS OF THE UNITED STATES. 



Splitrock pond, Passaic Co., N. J. 



Our species differs somewhat from the typical Norwegian 

 form, but I adopt the name for our variety. 



St. subarcuatum, Wolle. Plate XL VI. figs. 15, 16. 



This species is allied to the preceding, St. arcuaktm; I have 

 separated it because it is smaller, the aculei at the terminal 

 angles are not so long and the marginal granules are only 

 rarely bifid. In end view, the papilla-like granules are 

 arranged concentrically, often protruding on the margins. 



Since naming this desmid, three years since, I came across 

 varieties of St. Avicula coarsely granulate, which are very near 

 to this form. A variety of Avicula, would have been equally 

 appropriate. 



SECTION ill. 



MEMBRANE PILOSE, SPINOUS OB \< I l.i; \ I i:i>. 



St. aculeatum, Erhb. Plate XLV. figs. 1, 2. .">. 



Cells spinulose ; semicells with ~i< l<- somewhat drawn out, 

 margined with smaller aculei, and terminated by larger ones; 

 end view usually with three. but sometimes also with four 

 angles. 



Diameter without aculei about 50 />. 



Pond, near Minneapolis. Minn. Found no good specimens 

 elsewhere. 



Semicells are elliptic or fusiform, thickly spinulose, the 

 -pines usually simple, rarely divided at the apex ; the semi- 

 cells taper on each side into a short process tipped with three 

 or four larger aculei. 



This form agrees well with St. Saxonicum, Keinsch. Buln- 

 heim has a different form with the same name which I have 

 adopted in this monograph. 



St. telifeui \m, Ralfs. Plate XLV, tig. L 



Semicells more or less reniform, aculeated; the aculei larger 

 and most densely set at the angles ; end view triangular, sides 

 concave, angles broadly rounded and bristly. 



Diameter 33-38 fjt. 



Not rare in pond waters of New Jersey, Pennsylvania and 

 Massachusetts. 



