American Species of Marchantia. 231 



Epidermal pores usually surrounded by six ro.ws of cells, distinctly 

 cruciate; marginal scales not present; appendages of median scales 

 minutely and regularly crenulate or denticulate; rays of female 

 receptacle destitute of papillae; basal sinus scarcely or not at all 

 wider than the others. 



3. M. Berteroana. 

 Thallus with sclerotic cells : epidermal pores usually surrounded by five 



to seven rows of cells: marginal scales not present: rays of female 

 receptacle mostly five to nine, rarely more, flat to convex on upper 

 surface, never terete, destitute of papillae; basal sinus usually dis- 

 tinctly wider than the others : cupules destitute of papillae. 



Section II. Chlamidium. 

 Stalk of female receptacle with a single band of air-chambers. 

 Epidermal pores cruciate: appendages of scales entire or slightly 

 toothed: stalk of male receptacle destitute of air-chambers, with 

 two rhizoid-furrows ; rays short and broad : stalk of female 

 receptacle with two rhizoid-furrows ; rays long and narrow ; 

 involucre with ciliate lobes : cupules with dentate lobes. 



4. M. paleacea. 

 Epidermal pores not cruciate: stalk of male receptacle vith a single 



band of air-chambers and two to four rhizoid-furrows; rays 

 long and narrow (at maturity) : stalk of female receptacle with 

 two to four rhizoid-furrows ; involucre vaguely or not at all 

 lobed, entire to ciliate: cupules not lobed, dentate to ciliate. 

 Appendages of ventral scales sparingly crenulate or denticulate: 



rays of female receptacle short and broad, mostly eleven; 



involucre ciliate. 



5. M. breviloba. 

 Appendages of ventral scales usually closely denticulate or cilio- 



late: rays of female receptacle long and usually narrow. 

 Epidermal pores mostly 90-130 x 70-80/*: rays of female recep- 

 tacle slightly or not at all dilated at the apex, rarely emar- 

 ginate ; involucre crenulate to ciliate. 



6. M. domingensis. 

 Epidermal pores mostly 50-70 x 40-45M : rays of female receptacle 



distinctly dilated at the apex, usually emarginate; involucre 

 entire to crenulate. 



7. M. papillata. 

 Stalk of female receptacle with two bands of air-chambers and two 



rhizoid-furrows ; rays normally five, short and rounded, not dilated ; 

 involucre dentate to ciliate or laciniate: stalk of male receptacle 

 with two rhizoid-furrows: epidermal pores not cruciate: append- 

 ages of ventral scales entire to sparingly dentate: cupules not lobed, 

 dentate to ciliate. 

 Thallus thin and very delicate. 



8. M. Bescherellei. 



Thallus usually thick and firm. 



9. M. chenopoda. 



