148 FUNGUS-FLOEA. 



plane surface of the hymen ophore. We have in Britain a 

 distinct sequence from perfectly resnpinate forms to others 

 with a central stem and inferior hj'^menium. 



The genus PorotJielmm, hitherto included in the Pohjporeae, 

 belongs in reality to the Hydneae, the hymenium being 

 situated on the outside of the blunt spines, as in Hydnum, to 

 which genus it is closely allied, especially to those resupinato 

 species of Hydnum having the spines more or less indented at 

 the ajiex. Porothelium is distinguished by the blunt_ wart- 

 like spines that become distinctly indented at the apex. 



ANALYSIS OF THE SPECIES. 



I. Mesopus. 



Stem central or slightly excentric, pileus fleshy, hymenium 

 inferior. 



* Pileus fleshy, rather brittle. 

 ** Pileus corky or coriaceous. 



II. Pleuropus. 

 Stem lateral, hymenium inferior. 



III. Merisma. 

 Very much branched or tuberculiform. 



IV. Apus. 

 Sessile, dimidiate. 



V. Resupinati. 



Entirely resupinate, hymenium covering the free surface. 



* Spines fuscous or ferruginous. 

 ** Spines yellowish or greenish. 



*** Spines flesh-colour, liluc, or rufescent. 

 **** Opines white, often tinged with yellow or grey when 

 old. 



