52 DESMIDS OF THE UNITED STATES. 



base of the semi-cell, cytioderm firm, clothed with densely set 

 spines ; two or three rows around the apex firmer and longer 

 than the others. 

 Diameter 40-48 //. 



Pond, Dennis ville, New Jersey. 



D. crenulatum, Ehrb., D. nodosum, Bail., IK hirsuium, 



Bail., have features in common with this form. I have sepa- 

 rated it in view of the armor of spines with which it is 

 clothed; these are not hairs, nor gelatinous contraction.-, but 

 decided and firm spines. 



I). VEEBUOOBUM, (Bailey) Raits. Plate X. figs. 1, 5. 



Tolls cylindrical, tapering very Blightly from the centre to 

 the apex ; margins made crenate by numerous whorls of 

 quadrangular prominences. Length about twelve time- the 



breadth. 



I Hameter 2533 fi. 



Occur- frequently in ponds, Mt. Everett, Mass., and sparsely 

 in quiet water-, northern New Jersey. Bailey found it 

 originally in Rhode Island and New York. 



D. MINI-TIM, Kalf-. Hate L, tie-. 29-31. Plate X, Bg. !. 



slender, elongated, smooth, cylindrical, linear or slightly 

 tapering, ends round; 10-30 time- longer than broad; a 

 single inflation, more or Less prominent at the base of the semi- 

 cell. 



Diameter 7-! >>., or more rarely 10-12 u. 



Ponds, Florida, Massachusetts and New Jersey^ 



This minute plant is near a form described by Delponte as 

 /'. rectum but it has twice the diameter. Ralls describes his 

 D. minutum which has the same diameter as our-, only five 

 or six times longer than wide. Our forms vary greatly in 

 proportionate length and breadth ; the shortest however, is 

 ten times a- long as broad. They vary also much in thick- 

 ness and in the central inflation ; Bometimes the constriction 

 is barely perceptible, and again marked by a strongly 

 inflated border. The various forms frequently occur in 

 groups, and evidence specific relationship. 



D. TRIDENTULUM, W'olle. Plate X, fig. I<). 



Near the preceding in form and structure but average some- 



