80 DBSMTDS OF THE EXITED STATES. 



In front view, this is a common form, barely separable from 

 the following C. sublobatum ; in lateral, and in end view 

 however, they ought to be distinct by the absence or the 

 presence of a central inflation. All the specimens examined 

 personally, evidenced more or less of an inflation, or at least 

 a tendency to it; have not been convinced of having a 

 genuine, ('. Xymannianum. I set them down to C. sublobatum. 



Semicells with central inflation ; cytioderm smooth or punctate. 



C. sublobatum, Archer. Plate XVIII, figs. 21, 22. 



Cells somewhat oblong, about one-half longer than broad, 

 sinus lincai-; semicells swollen at the base, gradually nar- 

 rowed towards the truncate ends ; inferior and superior angles 

 rounded; apex broadly truncate, sides sinuate; with central 

 inflation. 



1 diameter 38-44 //. 



Ponds, Pennsylvania, New .Jersey ; not abundant but 

 probably widely distributed. 



C. BETU8UM, Perty. Plate XVIII, figs. 25, 26. 



Small, of nearly equal length and breadth, entire; sinus 

 deep, linear ; semicells with subreniform base, sides -innate 

 and converging to a truncate end ; angles rounded ; end view 

 centrally protruding. 

 Diameter 22-30 />.. 



Pennsylvania and New Jersey. 



C. MARGABITUM, Wolle. Plate XIX, tigs. 25, 26, 27. 



Suborbicular, from one t and one-third times as long 



as wide; sinus narrow linear; semicells somewhat semi- 

 circular, margins undulate-crenate, or emarginate; two or 

 three surface swelling- near the base which cause prismatic re- 

 flection.- from the smooth pearl-like membrane. 

 I diameter 22-25 //. 



Found the first of this form in Splitrock pond, New Jersey, 

 but occasionally since in other localities of the same State, 

 and in Pennsylvania. 



C. TTTBOPHORUM, Xord. Plate XIX, tigs. 28, 29, 30. 



Cells about as long as wide, circular, deeply contricted ; 

 sinus an acute angle considerably amplicated (angle about 20); 



