61) DESMIDS OF THE UNITED STATES. 



hack circularly arched, base concave ; angles of the two semi- 

 cells, more or less acute, approximate closely. (Ytioderm 

 punctate; isthmus usually less than one-third of the diameter. 

 End view elliptical ; side view circular. 



Diameter 25-28 //. 



Brown's Mills, N J. 



C. a<ti.kati m, Wolle. Plate X V I , fig. 15. 



.Medium size, suborbicular, length slightly less than the 

 diameter; constriction deep, forming, by the incurving of the 

 angles of the semicells, two elliptical sinuses; cytioderm 

 primarily more or less densely aculiated ; later the aculei drop 

 off and leave short granule-like stumps; end view elliptical. 



Diameter 33 /i.; length 30 //.; breadth of constriction 10//. 

 Pond, Minneapolis, Minn. Collected by Miss E. Butler, 

 1882 and 1883. 



( '. SMOLANDICUM, Lund. Plate XVI. figS. 35, 36. 



('ells somewhat longer than wide ; isthmus narrow, constric- 

 tion deep, sinus narrow linear ; semicells semicircular with 

 Straight base and arched hack sometimes suhtruncate, angles 

 (inferior) obtuse, mounted with a papilla ; end view elliptical ; 

 lateral view circular. Membrane distinctly punctate. Chloro- 

 phyl masses two in each semicell. 



Diameter 34-48 n. 



Various localities, Pennsylvania and New Jersey. 



Usually the cells are about one-eighth longer than hroad ; 

 they vary considerably in size. At Pleasant Mills, New 

 Jersey, there is a variety which is somewhat depressed, meas- 

 uring one-eighth less in length than breadth. The distin- 

 guishing feature of this species i> the papilla at each angle. 



C. EXIGUUM, Archer. Plate X V I , figs. 13, 14. 



("ells very small, smooth, oblong, 1J 2 times as long as 

 hroad ; medial constriction slight ; semicells subquadrate, 

 containing one chlorophyl nucleus; end- obtusely rounded. 

 I Hameter 12-15 n. 



Florida, collected by J. D. Smith, 187*. 



C. notabile, Breb. Plate XVI, fig. 11. 



( Jells small, about twice as long as broad, margins entire or 

 moderately undulate-crenate ; end- truncate; semicell more 



