50 DESMIDS OF THE UNITED STATES. 



the finest specimens in Green Pond, commonly several united ; 

 had as many as ten cells in a series. They are without a 

 suture, and apparently without vacuoles. 



D. constrictum. Bail. Plate XI, rig. 2. 



Cells with moderately dee] ostrietions, which separate 



four equal, gently curving prominences <>n each semi-cell; 

 end view entire. Apex furnished with a few conspicuous 

 teeth of which four are ordinarily in view. Plant 10-12 

 times longer than broad. 

 Diameter t0 50 fi. 



This species bears 3< similarity to />. nodosum in its 



wavy margins, but tie- undulation- an- less prominent, 

 and the transverse Bections are quite distinct, in the one they 

 arc circular in the other undulate ; compare Plate XI, fig. 11, 

 sections of l>- nodosum. 



D. NODOSUM, P.ail. Plate XI, figs. 11, 12, and Plat.- XII, tig. 20. 

 Semi-cell- with four prominent nodes separated by constric- 

 tion- ; end view -i.\ eremite, formed by whorls of tubercles ; 

 8-K> time- longer than broad. 



Diameter 4555 ,". in centre; end- about hall' as thick. 

 Frequent in ponds, Pennsylvania, New Jersey, Massa- 

 chusetts. 



D. KEPANDUM, Wolle. Plate XI, fig. 1. 



Smooth or punctate, aboul twenty time- longer than broad, 

 margins repand or undulate from the base of the semi-cell to 

 near the end ; only slight variation in diameter from base to 

 end ; apices tnuicatelv rounded, and sometimes slightly dilated. 

 No suture. 



Diameter 25 y. 



Sparsely found in Pennsylvania and New Jersey. 



D. DILATATUM, (Cleve) Lund. Plate L, fig. 32. 



Cell- -lender, cylindrical. 15-20 times longer than broad, 

 undulate-nodose; base moderately inflated and longitudinally 

 plicate; no suture evident; semi-cells usually with eight in- 

 flation- and corresponding constrictions ; apices roundly trun- 

 cate and more or less dilated. 

 Diameter 1316 ;>.. 



Brown's Mills, and other ponds, New Jersey. 



