COSMAEIUM. 91 



The plants recognized by different authors as of the present 

 species, by their protracted ends of the cells, are very variable 

 in size and detail of form. Plate XX, figs. 27, 28 represents 

 the true form ; from pools in marshy grounds, Pennsylvania. 

 Fig. 29 is another form, less than half the size, found in num- 

 bers in a pond near Branchville, Sussex County, N. J. Plate 

 LX, fig. 22, is a third variety from Minnetonka Lalie, Minn., 

 intermediate in size, but so closely related to C ornatum in 

 size, form, and arrangement of granules, I call it a variety of 

 that species. The other (fig. 29) is evidently of the same 

 connection, hence I transfer it from the position given it by 

 Naegeli to companionship with the latter. 



C. COMMISTJRALE, Breb. Plate XXI, figs. 49-51. 



Semi-cells short reniform, three times broader than long, 

 rough with pearly granules ; end view with a constriction 

 between the central inflation and the extremities. 

 Diameter 34-38 n. ; length 25-30 yU. 



Sparsely found in ponds in Pennsylvania, New Jersey, New 

 Hampshire, and probably most of the States. 



C. STJBCEENATUM, Hantzsch. Plate XXI, figs. 6, 7 ; Plate XXII, 



fig. 20. 



Cells with apices or ends more or less distinctly quadri- 



crenate, sides with (4-) 6 crenae; within the margins three 



or four series of granules ; the swelling near the basal line 



has usually five short series of granules ; viewed from the 



vertex, elliptic, apices truucate-retuse, sometimes rounded ; 



on the swollen middle are often seen five prominent granules ; 



lateral view, ovate, with basal swellings and truncate ends. 



Diameter 20-26 fx. ; length 23-36 yu. 



Ponds, and sluggish streamlets, Pennsylvania, New Jersey, 

 Massachusetts, Minnesota. 



C. PEOTTJBEEANS, Luud. Var. GEANDLATUM, Wolle. Plate 

 LXII, figs. 13, 14, 15. 

 Cells about one-fifth longer that broad ; constriction deep, 

 narrow linear ; semi-cells nearly twice as wide as long, base 

 straight, sides somewhat diverging from the basal line ; 

 superior angles nearly right, inferior angles obtuse ; near the 

 middle of the cell is a small granulated tumor ; seen from 

 the vertex elliptic with a central swelling on each side; 

 lateral view nearly spherical ; membrane granular. 



Diameter 25-28 /<. 



From a small pond near Minneapolis, Minn. This desmid 

 . is evidently not. the same as found in Sweden and described 



