168 THE AMEEICAN MONTHLY [September, 



tt. End vicAV margins smooth ; spines short ; semi-cells in front view 3 or 



4 times as wide as long commutahim^ 124 



//. End view margins smooth ; spines very long . . lotigisfinum^ 145 

 tt. End view margins verrucose, the verrucae emarginate or not, 



forjiciilatiim^ 144 

 tt. " " dentate, angles usually 3 . . mo]iticuIos7i}n^ 144 



uu. End view^ margins smooth, concave ; angles notched 



qiiadraiigiilare., 145 

 tiu. " " crenate ; spines long, divergent, iVc>2;^C<^5ar<?^, 145 



uu. " " spinous ; angles produced, furcate, _/c>;;yz'c?//a/?/»?, 144 



vv. End view triangular ; aculei short, Hystrix^ 142 ; tridentiferum., 142 

 vv. " " spines long, colorless . . tricorfttitiim., 145 



vv. End view 4-angled, angles broadly rounded, spines scattered ; sides 



concave Hystrix., 142 



vv. End view t^-angled, sides concave Brasiliense., 146 



WW. Angles with numerous setae as long as the lobes; cells in front view 



cruciform crziciatum., 142 



WW. Angles wath 4 teeth, 2 projecting upward, 2 downward, cerbei'tis., 142 

 WW. " 2 spines ; margins concave, spinous . quaterniiim.! 144 



XX. Sides unequally produced, spinulose or spinous . controversum., 143 

 XX. Sides equally produced, spineless ; angles spinous . aculeattim., 140 

 yy. Diameter ^lo in. (38//) or less {zz) . 

 yy. Diameter greater than (38,a) g-|-g- inch ^A). 

 zz. Cytioderm aculeated, aculei larger and denser at the angles, 



teliferum., 140 

 zz. Cytioderm aculeated except at the centre, echinatimi., 141 ; pecten., 141 



zz. " spinous; margins dentate, convexum.* 



zz. " " margins crenate, Ravenellii^ 143 



A. Cytioderm aculeated, aculei geminate, sociatum., 142 



A. " '• aculei not geminate, densest at the angles, 



JB7'ebisso?inii., 141 

 A. " '' aculei evenly covering the surface, 



Saxouiciim^ 141 ; hirsutzitn., 141 

 A. Cytioderm spinous, spines not notched, .... echinatum^ 141 



A. " •' spines or short processes notched,. v^ow^/c>.s-?^;«, 148 



B. End view 3-angled ; processes within the margin, 6 in number ( C). 

 B. " " " " " " 3 in number (Z>). 

 B. " " " processes both on and within the margins (-^). 

 B. " " " processes at the angles only {E^ • 



B. End view 3 or 4-lobed, emarginate or bifid ; cell very irregular or 



quadrate, enornie., 151 



C. Front view lateral margins crenate ; basal margins crenate, 



eusteph a n u m , 147 



C. " lateral margins smooth, . . . psetidoftircigerum., 147 



C. " lateral margins with 3-6 sharp teeth : basal margin smooth 



ctmeatmn ., 148 



D. Cytioderm granular, furcigerum, 146 



D. Cytioderm smooth ; end view angles produced into 2 pi'ocesses, a third 



above and between them, Pottsii., 151 



D. Cytioderm smooth or finely punctate ; end view angles notched, 



Kitchellii., 150 



E. Processes 9, nearly as long as semi-cell diameter, ends furcate, 



ToJiopekaligense.\ 



* Journ. R. Micv. Soc, Feb., 1886. + Bulletin Torrey Botanical Club, Dec, iS 



