326 SYSTEMATIC 



XXVI. THELOTREMACEAE 



A tropical or subtropical family of which the leading characteristic is 

 the deeply sunk disc of the apothecium : it has a proper hyphal margin, 

 and, round that, an overarching thalline margin. The apothecia occur singly, 

 or they are united in a kind of pseudostroma : in Tremotylium several grow 

 together, while in Polystronia each new apothecium develops as an outgrowth 

 from the thalline margin of the one already formed, so that an upright, 

 branching succession of fruits is 'built up. It is a very unusual type of lichen 

 fructification, with one species, P. Ferdinandezii, found in Spain and in 

 Guiana. 



The thallus in all the genera is crustaceous with an amorphous (decom- 

 posed) cortex; or it is non-corticate. The algal cells are Trentepohlia except 

 in Phyllophthahnaria, an epiphyllous genus associated with the alga Phyco- 

 pcltis. In Polystronia the alga is unknown. 



Only one genus is represented in the British Isles. 



Apothecia growing singly. 



Thallus with Trentepohlia gonidia. 



Paraphyses numerous, unbranched, free. 

 Spores colourless. 



Spores elongate, 2- or multi-septate I. *Ocellularia Spreng. 



Spores muriform 2. Thelotrema Ach. 



Spores brown. 



Spores elongate, septate 3. *Phaeotrema Mull.-Arg. 



Spores muriform 4. *Leptotrema Mont. 



Paraphyses scanty, branched. 



Spores muriform, brown 5. *Gyrostomurn Fr. 



Thallus with Phycopeltis gonidia 6. *PhyllophthalmariaA. Zahlbr. 



Apothecia in pseudostromata. 



Apothecia united in tubercles 7. *Tremotylium Nyl. 



Apothecia united by the margins 8. *Polystroma Clem. 



XXVII. DlPL OSCHIS TA CEA E 



Scarcely differing from the preceding family except in the gonidia which 

 are Protococcaceous algae. The thallus is crustaceous and non-corticate. 

 The apothecia have a double margin but the outer thalline margin is less 

 overarching than in Thelotremaceae. The spores in the two genera are 

 somewhat peculiar: in Conotrema they are exceedingly long and divided 

 by parallel septa into thirty to forty small cells; in Diploschistes ( Urceolaria) 

 they are large, muriform and brown. Conotrema contains two corticolous 

 species ; Diploschistes about thirty species mostly saxicolous. Both genera 

 are represented in the British Isles. 



Spores elongate, multi-septate, colourless i. Conotrema Tuck. 



Spores muriform, brown 2. Diploschistes Norm. 



