34 ANGIOCARPOUS LICHENS. 



The distinguishing characteristic of this tribe is the 

 carbonaceous perithecium. This, in the typical genus 

 Verrucaria, is either entire, i. e, completely surrounding 

 the nucleus on all sides (see Plate XV. fig. 3. A a.), 

 or dimidiate, covering the upper portion only of the 

 nucleus, but deficient at, and not subtending the base. 

 (See Plate XVII.) The perithecia are usually pro- 

 minent, more or less immersed in the thallus, round or 

 globose, not attenuated into a neck, perforated at the 

 apex with a large and distinct pore. The interior is 

 lined with a thin membranaceous tunic, usually pale- 

 coloured, sometimes black (see Plate XV. fig. 3. A d.), 

 enveloping the nucleus (see Plate XV. fig. 3. ^ c), which 

 is usually white, gelatinous, sub-hyaline, consisting of 

 asci enclosing sporidia. 



Genus I. SegesTRELLA, Fries. 



Perithecium solitary, ceraceo-membranaceous (coloured), 

 ostiolum simple, subpapillate, nucleus gelatinous, sub- 

 hyaline; thallus crustaceous. 



1. S. THELOSTOMA, F)ies. Sporidia 8 in asci, elliptical, 

 margined, pale yellow. Plate XV. fig. 2. 



Vekrtjcaria THELOSTOMA, Jck. ill "Wilicli. ii. 44. (1807.) 

 Lichen thelostomus, Sm. E. Bot. 2153. (1810.) 

 Pyeentjla umbonata, Jc/i. L. Univ. 316. (1810); Syn. 121. 

 Segestrella THELOSTOMA, Fnos, L. Eef. 429. (1831.) 

 Lecanora THELOSTOMA, Rook. Br. El, ii. 189. (1833.) 



Near Eglestone, Durham ! Mr. Borrer, 



In this plant there is certainly no appearance of a 



and ' difflueni in the latter. I suppose, therefore, that by ' diffluens' he 

 means (not fluid or dissolving, but) of loose structure, not compact, such as 

 is found in the disc of Parmelia, &c., yet not 'fatiscens' as in Sphserophoreae. 

 Yet, if I am right in this conjecture, the distinction seems to have been an 

 afterthought ; for in the ' Clavis Dispositionis,' p. 8, he gives the Verrucarieae 

 a deliquescent nucleus. He uses the terra again, too, in the char, of the 

 genus Verrucaria." Mr. Borrer, in lit. 1850, 



