FAMILIES AND GENERA 331 



which grows out from all sides and meets across the opening. The overlying 

 layers, with gonidia, follow more slowly, but they also in time become 

 continuous, so that the "erose" character persists only near the periphery. 

 This forward growth of the lower thallus occurs in other species, though to 

 a much less marked degree. 



There is abundant detritus formation in this family; the outer layers of 

 the cortex are continually being sloughed, the dead tissues lying on the 

 upper surface as a dark gelatinous layer, continuous or in small patches. 

 On the under surface the cast-off cortex gathers into a loose confused mass 

 of dead tissues. 



Asci 8-spored. 



Spores mostly simple (disc gyrose) i. Gyrophora Ach. 



Spores i-septate 2. *Dermatiscuni Nyl. 



.'^.sci i-2-spored. 



Spores muriform 3. Umbilicaria Hoffm. 



XXXV. ACAROSPORACEAE 



Thallus foliose, squamulose or crustaceous, sometimes scarcely developed. 

 Algal cells Protococcaceae. 



Into this family Zahlbruckner has gathered the genera in which the 

 asci are many-spored, as he considers that a character of great importance 

 in determining relationship, but he has in doing so overlooked other very 

 great differences. The fruit-bodies are round and completely enclosed in 

 a thalline wall in Thelocarpon, which has however no perithecial wall. They 

 have a proper margin only (lecideine) in Biatorella, and a thalline margin 

 (lecanorine) in the remaining genera. In Acarospora the apothecia are sunk 

 in the thallus. Stirton's genus Cryptothecia'^ is allied to Thelocarpon in the 

 fruit-formation, but the basal thallus is well developed and the spores are 

 few in number and variously divided. 



Thallus none. 



Apothecia (or perithecia) in thalline warts i. Thelocarpon Nyl. 



Thallus crustaceous. 



Apothecia lecideine ; spores simple 1. Biatorella Th. Fr. 



Apothecia lecanorine ; spores septate 3. *Maronea Massal. 



Thallus of small squamules 4. Acarospora Massal. 



Thallus almost foliose, attached centrally 5. *Glypholecia Nyl. 



XXXVI. Ephebaceae 



A family of very simple structure either filamentous, foliose or crustaceous. 

 The algal cells which give a dark colour to the thallus are Stigonenia or 

 Scytonema, members of the blue-green Rlyxophyceae, and consist of minute 

 simple or branched filaments — single cell-rows in Scytonema, compound in 

 Stigonema. 



^ Stirton 1877, p. 164. 



