COSMARIIM. 75 



retuse near the apices ; for perfect identity the ends ought 

 not to be retuse ; my specimens are slightly concave. 

 Size about the same as the typical plant. 



Found this variety in collections made by Miss E. Butler, 

 Minneapolis, Minnesota, and by A. D. Balen, Plainfield, 

 New Jersey. 



C. PSEUDOPYRAMIDATUM, Lund. Plate XVIII, figs. 11, 12. 



In habitat, in form and proportions like the true plant, 

 but only about half the size. It corresponds with C. pyra- 

 midatum, variety minus, Eeinsch ; Eab. Alg. Exsic. No. 1902. 



Besides these, Ealfs has a Forma major, which I have in- 

 cluded in my general grouping (fig. 17). 



C. KALFSII, Breb. Plate XVIII, fig. 1. 



Orbicular or suborbicular, deeply constricted, sinus narrow 

 linear ; semi-cells nearly semicircular ; inferior angles ob- 

 tuse, dorsum high convex ; cytioderm smooth or finely 

 punctate. 



Diameter 60-100 ,u. ; length 70-120 yu. 



Pennsylvania, New Jersey, not frequent, but turns up every 

 now and then, sometimes in considerable numbers. 



In size, form, and arrangement of chlorophyl, this species 

 is often a good representative of C. Candianum, Delp. 



C. PACHYDERMUM, Lund. Plate XVIII, figs. 2, 3. 



Cells li-13 times longer than broad; sinus narrow linear; 

 semi-cells with straight base, rounded angles ; sides rise 

 nearly at right angles and then converge, forming a high 

 arch ; they contain two chlorophyl masses ; viewed from 

 the vertex, oval ; isthmus wide, cytioderm firm, distinctly 

 punctate. 



Diameter 75-100 /v. 



Had specimens from Budd's Lake, New Jersey ; from Ne- 

 braska Notch, Vermont, collected by C. G. Pringle ; and from 

 Mt. Everett, Massachusetts. 



This species is separated from C. JSaf/sii, by its usually 

 greater proportionate length, firmer cytioderm, and wider 

 isthmus. 



. GALERITUM, Nord. Plate XIX, figs. 46, 47, 48. 



Cells slightly longer than wide, with narrow isthmus, 

 deep constriction and narrow, slightly gaping sinus ; semi- 

 cells triangular with straight, or somewhat reniform base, 

 rounded lower angles, convergent, straight, or slightly con- 



