34 



COLLKMACEI. 



[pterygium. 







-^ :'xA, j>.r 



Fig. 6. 

 Pterygiura cmtrifuguvi Nyl. — a. Longitudinal section of tliallus, X 27-5. 

 h. Transverse section of the same. c. Vertical section of a sperniogone, 

 X42. d. Jointed sterigmata. 



This genus is analogous to FanmHarui among the Lichenacei, from 

 which, howeTer, it is distinguished by the absence of a hjiioth alius. In 

 this country few species have occurred, but probably others will be 

 detected. 



1. P. centrifugum A^yl. BuU. Soc. Bot. i. (1854) p. 328; Syn. 

 i. p. 92, t. ii. ff. 11-15. — ThaUus smaU, laciniato-radiate, centrifu- 

 gal, dark- or chestnut-browu, often blackish in the centre ; laciniae 

 divaricato-multifid, plane or somewhat convex, narrow, crowded, 

 very thinly longitudinally rugulose. Apothecia unknown. 



Externally this looks like a small Physcia near to dark vars. of Ph. 

 ohseura ; but its anatomical structure is essentially different. The thallus 

 is only about | inch in diameter (even smaller in the only Briti.sh spe- 

 cimen seen), and is more or less centrifugal. The gouimia are pale- 

 greenish, often moniliform towards the upper sui'face. No apothecia 

 have yet been detected, but the spermogones (not present in our spe- 

 cimen) are known ; they ai'e tuberculose, usually blackish above, with 

 multi-articulate sterigmata ; spermatia straight, slightlv acute at the 

 apices, 0,005-0,006 mm. long, 0,001 mm. thick. 



Hnh. On calcareous rocks in a subalpiue hilly district. — Didr. Extremely 

 local and scarce, having been found only veiy sparingly in S.W. England. 

 — B. M. : Cheddar ClilFs, Somer.setshire. 



2. P. pannariellum Nyl. Rallsk. pro F. ct Fl. Not. iv. (1859) 

 p. 236 ; Flora, 1S()0, ji. 41. — Thallus moderate, laciniato-radiato 



