96 DESMIDS OF THE UNITED STATES. 



margin; semicell broadly elliptic, with a single outwardly 

 curved aculeus at each end. 



Diameter of cell without aculei 38 //.; with aculei 63 ji. 

 This species was collected with swamp moss (Sphagnum I, by 

 E. A. Rau, in a pond near Newfield, N. J. It bears some 

 resemblance to A. divergens, Kab., but it is not subtillissime 

 verruculosus ; also to A. quadridens, Wood, but it is twice the 

 size of that plant, and not quadridens. 



A. ovalis, Wollc. Plate XXIV, tigs. 13, 14. 



Cell small, smooth, often about one-fourth longer than wide, 

 semicells oval, armed at each end with a straight or diverging 

 aculeus. 



Diameter 20 //., without aculei. 

 Ponds, Mt. Everett, Mass. 



The smaller size, the straight, erect or slightly diverging 

 spines, I consider sufficient to separate this form from A. 

 eonvergens. 



A. bubulatus, Kg. Plate XXIV, tigs. 11, 12. 



Semicells elliptic, larger than the preceding, with long, sub- 

 ulate, erect or somewhat diverging spines. 

 Diameter 30-3o u. 



Ponds, New Jersey, rather rare. I have somewhat modi- 

 fied the original diagnosis, by putting dim rging for converging \ 

 ami thus claim for this plant a distinct position. 



A. orbicularis, Wblle. Plate X X I Y. figs. 15, 16. 



Very small, smooth, orbicular ; semicells united by a nar- 

 row isthmus; aculei of the two semicells nearly parallel. 



Diameter, without aculei, 12 u. 

 Ponds, Mt. Everett, Mass 



A. QUADRIDENS, Wood. Plate XXIV, tigs. 17, 18. 



Broadly oval or suborbicular, a little longer than broad, 

 with the margin crenately undulate; semicells somewhat reni- 

 form, at each end armed with a subulate, moderately robust, 

 acute, recurved. large spine; cytioderm with a few smallish 

 tubercles arranged in three or four row- ; semicells from the 

 vertex acutely elliptical, with the margin crenate and the sur- 

 face sparsely warty. 



1 diameter 19 ;i. ; length 30 fi. 



Saco Lake, N. H., (Lewis) Wood. 



