CO6MARIUM. 97 



C. PYCNOCHOXDRUM, Nord. Plate XXII, figs. 10, 11. 



About one-fifth longer than the diameter; subhexagonal, 

 constriction deep, sinus narrow linear; ends truncate quadri- 

 crenate ; angles inferior and superior obtusely rounded ; 

 sides moderately convex with about six crenae each; at base 

 nine to twelve vertical, or somewhat diverging series of 

 granules ; membranes ornate with additional granules ar- 

 ranged in lines, at the same time radiating and concentric ; 

 the former courses are double, and often triple near the 

 margin; central area within the concentric rows, is nude. 

 Seen from the vertex, or from the side, a basal inflation is 

 evident ; thickness of the cells, equal to about half the 

 length; isthmus measures about half as much as the breadth. 



Diameter 50 ^. ; length 79 /v. 



The only locality from which I had this form is Nebraska 

 Notch, Vt., from collections made by C. G. Pringle. It differs 

 from the typical, Arctic (Spitzbergen) form in its greater pro- 

 portionate length. 



C. PULCHERRIMUM, Xord. Plate LX, figs. 25-27. 



Cells oblong, ends rounded, about one-third part longer 

 than broad, margins crenulate, constriction deep, sinus nar 

 row linear, not ampliated towards the mouth ; semi-cells 

 subsemicircular, inferior angles square, basal center inflated 

 and furnished with about five vertical series of granules ; 

 lateral view broadly ovate, end rounded, and base of each 

 side more or less inflated; membrane granulate near the 

 margins, granules arranged in about four to five concentric 

 series ; area nude between these and the vertical series. 



Diameter 33 /<. ; length 40 /<. 



This desruid is proportionately shorter than the typical 

 forms described by Dr. Nordstedt. The one from Brazil and 

 the other from the island of Spitzbergen, which measures one 

 and one-third to nearly twice as long as wide. My specimens 

 are from Minnesota, and from several localities of eastern 

 Pennsylvania. 



. RADIOSUM, Wolle. Plate XXII, figs. 21, 22. 



Cells orbiculate, about one-eighth longer than broad ; semi- 

 cells semicircular, separated by a deep narrow linear sinus ; 

 ends round or slightly depressed, clothed with semiorbicular 

 granules arranged in about thirty-five radiating lines; basal 

 inflation has about eight vertical, or somewhat diverging 



