COSMARIUM. 85 



Frequent in ponds, Pennsylvania, New Jersey, Massachu- 

 setts, Minnesota and Connecticut. 



C. ORBICULATUM, Kalfs. Plate XVII, figs. 20, 21. 



Twice as long as wide ; semi-cells spherical, connected by 

 a narrow isthmus ; cytioderm covered with large granules. 

 Zygospore, according to Kalfs, orbicular, studded with large 

 verrucae. 



Diameter 20-33 JJL. 



Met with it frequently in ponds of New Jersey and Penn- 

 sylvania. 



C. EXCAVATUM, Nord. Var. dnplo major, Lund. Plate LXIV, 



figs. 14, 15. 



Cells nearly twice as long as wide, constriction wide and 

 deep; end view orbicular ; semi-cells snbspherical with trun- 

 cate base ; verrucae of membrane, producing a crenulate 

 margin. 



Diameter 21-25 //. 



Not rare in ponds, Pennsylvania, New Jersey, etc. 

 Wille, of Norway, describes a form "elliptica," most nearly 

 allied to ours in front view, but elliptical in end view. Nord.'s 

 and Lund.'s described forms are orbicular in end view. 



Var. TRIGONUM, Lagh. Plate XLIX, figs. 24, 25. 



Cells in vertical view triangular, sides straight, or some- 

 what convex, angles rounded. 



Diameter of cells 18 /v. ; length 20 //. ; thickness 18 fit. 

 Tewksbury, Massachusetts. 



C. SUBORBICULARE, Wood. Plate XXVII, fig. 24. 



Cells small, a very little longer than broad, with the margin 

 irregularly crenate, or crenate undulate ; semi-cells from the 

 side orbicular, from the vertex elliptical ; sinus very narrow, 

 but within somewhat excavated ; cytioderm thick, sparsely 

 coarsely granulated; granules subdistant, in each cell ar- 

 ranged in one or two curved marginal series and in a central 

 group of two or three short rows. 



Diameter 30 //. ; length 33 //. 



Saco Lake, New Hampshire, (Lewis). 



C. AMOENUM, Breb. Plate XVII, figs. 5, 6, 7. 



Cells twice as long as broad, sides parallel, ends rounded ; 

 constriction deep, linear ; semi-cells rough with large, obtuse, 

 papilla-like pearly granules ; side view much compressed, 

 about thrice as long as broad ; semi-cells contain two chlo- 

 rophyl nuclei. 



