26 DESMIDS OF THE UNITED STATES. 



Zygospore spherical, formed by the conjugation of two 

 cells, the clorophyl passing through a gelatinous connecting 

 tube from one cell to the other (figs. 3, 4). 



Specimens occur frequently in pools and ponds all over the 

 country, rarely nnmingled with other forms. It is readily 

 distingushed by its large size, deep incisions of the border, 

 and twisted outline. 



D. QUADRATUM, Nord. Plate LX, fig. 5. 



1 Mffers from the preceding in the cells being nearly as long 

 as broad, and viewed from the side, quadrate. The breadth 

 of the cells is only about one-fifth nioie than the length ; the 

 thickness, the same as the length. Chlorophyl mass in each 

 cell in end view, more or less radiate. 



Diameter 45 //. : length, 33-3S jw. : thickness, 33-3* //. 



Found this form repeatedly during the past four years, but 

 rarely, except in ponds, Brown's Mills, New Jersey. It varies 

 in size from the Norway typical plant, in being considerably 

 larger ; othewise it appears to be identical. 



D. LOXGATUM. Wolle. Plate LX, fig. 6. 



Filaments thin ; cells in front view nearly twice as long as 

 wide : in side view nearly 2* times longer than broad : closely 

 united without a thickened border at their junction ; end 

 view broadly elliptic. 



Diameter, widest part, 25-28 M- ; thickness, 16-18 //. ; length 

 of cell, 35-40 yw. 



This interesting new species from Brown's Mills and Egg 

 Harbor, New Jersey, was found late in the season (September 

 22, 1883) ; no gelatinous sheath was observable ; the filaments 

 were hyaline except two chlorophyl nuclei in each cell. 



D. SWARTZII, Ag. Plate II, figs. 1-6. 



Filament triangular, with a single longitudinal, waved, 

 dark line, formed by the third angle, (compare figs. 6, 8, 13) ; 

 joints in front view somewhat quadrangular, broader than 

 long, with two slightly angular crenatures on each lateral 

 margin, united at the whole of their end margins by a thick- 

 ened border; end view triangular with the chlorophyl three- 

 rayed. Zygospores oval. 



Diameter 36 yu., more or less. 



Frequent in shallow pools, trenches and the like. 

 The spores are formed by the flowing together of the two 

 masses of chlorophyl in each cell ; the united body assumes a 



