COSMARItTM. 



the true form, I consider it merely a variety of C. ornatum. 



Plate X VII, fig. 29, is a g 1 representation of < '. protrcustwm, 



Naeg., Inn the specimens, found in large numbers, clearly 

 show their connection with C ornatum. Compare note under 

 C. protractwm. 



C. s|.,,i:tki.i.\. Breb. Plate XLIX. figs. 28-30. 



\'ei'\ nearly as long as broad, deeply constricted ; semicells 

 Bubreniform, Bides somewhat dilated and rounded, end broadly 

 truncate, margins erose-spinous or denticulate; cytioderm 

 granular. 



Diameter 31 1-36 .. 







Harvey Lake, Luzerne County, i'a. Bean some resem- 

 blance to C. nnnitiim, hut ends do not protrude; granules 

 are more Bpinoua than rounded, producing the erose appear- 

 ance of the margins. Pound many specimens in this one 

 locality, hut did not recognize the form elsewhere. 



C. pbotractum, Naeg.) Archer. Plate XVII, figs. 27-28. 



But slightly Longer than wide, constriction deep, sinuses nar- 

 row linear, often ainpliated from the acute angles : semioelhi 

 with tumid base, twice as broad as long, angles rounded, Bides 

 deeply sinuate below the truncate end. Viewed from the ver- 

 tex, elliptic with a central inflation ; membrane granular. 



Diameter 70-80 a. 



The plant- recognized by different authors a< of the present 

 species, by their protracted ends of the cells, are very varia- 

 ble in size and details of form. Plate XVII, tigs. 27, 28 

 represent the true form ; from pools in marshy grounds, 

 Pennsylvania. Fig. 29 is another form, less than half the 

 size, found in numbers in a pond near Branchville, Sussex 

 County, N. J. Plate XLIX, fig. 22 is a third variety from 

 Minnetonka Lake, Minn., intermediate in size, but so closely 

 related to C. ornatum iu 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. commisurale, Breb. Plate XVIII, figs. 49-51. 



Semicells short reuiform, three times broader than long, 



