OPEGEAPHA. 



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times arranged in a single vertical series like a row of beads, 

 or transversely in several rows. 



Genus I. OPEGRAPHA, AcL 



Gen. Char. Apothecia lirellate, sessile. Perithecium carbona- 

 ceous, entire, — that is, surrounding the sides and base of thala- 

 mium, which is rimseform or canaliculate, having a prominent, 

 proper margin. Thallus crustaceous or membranaceous. (Name 

 from oirrj, hollow, and ypacfrrj, writing ; also popularly called 

 " Chink-wort.") 



* Saxicolous species. 



1. Opegrapha saxatilis. Thallus pulverulent, chalky- 

 white ; lirellse prominent, rigid, straight or stellate- diver- 

 gent, tapering towards each extremity. Spores eight in 

 each theca, obtusely or subclavately fusiform, five to seven- 

 septate ; central cell largest, pale yellow. (E. B. 1790.) 



Common on various rocks and stones, as limestone and 

 sandstone, as well as on mortar, in various parts of Britain. 

 The spermogones may sometimes be discovered as black 

 points on the surface of the thallus ; they are globular, uni- 

 cellular, with a thin brownish capsule. The sterigmata are 

 short and linear ; the spermatia straight, of great tenuity, 

 and very numerous. 



