LEPTOGI0SI.J COLLEMEI. 67 



8. L. cretaceum Nyl. Act. Linn. Soc. Bord. ser. 3, i. (1857) 

 p. 270 ; Syn. i. p. 120. Thallus rosulato-lobulate or stellato-laci- 

 niate, olive-brown or dark-olive ; the lobes unequal, crenate, almost 

 imbricate. Apothecia small, nearly biatorine, concave or gyalecti- 

 form, pale reddish-brown, the margin entire, paler ; spores ovoid, 

 3-7-septate, with longitudinal septa, 0,022-40 mm. long, 0,011- 

 17 mm. thick. Mudd, Man. p. 45 ; Cromb. Lich. Brit. p. 7 ; Leigh t. 

 Lich. Fl. p. 32, ed. 3, p. 27. Enchi/lmm cretaceum Gray, ISTat. Arr. 

 i. p. 398. Oollema cretaceum Sm. Eng. Fl. v. p. 210. Lichen 

 cretaceus Eng. Bot. (1800) t. 738. 



This plant appears at first as minute, very thin, olive or dark stellte, 

 somewhat immersed and distinct. These become more prominent, ap- 

 proximate and confluent, till it attains the perfect state. It is occasionally 

 seen in an isidiomorphous condition. The gonimia are rarely moniliform. 

 The apothecia, seen only in the best developed specimens, are small in 

 the scattered, and moderate in the confluent rosulce. 



Ilab. On cretaceous and siliceous nodules in moist shady places in 

 upland tracts. Distr. Confined to the Chalk and Oolite districts of S. 

 and W. England ; probably in its young state often overlooked. B. M. : 

 Near Folkestone, Kent; Plumpton and West Dean, Sussex; Reigate 

 Hill, Surrey ; Isle of Wight ; Brighton Downs, Sussex ; near Northleach, 

 Gloucestershire; Stokesay, Shropshire. 



9. L. microscopicum Nyl. Bull. Soc. 

 Bot. Fr. iv. (1857) p. 920; Syn. i. 

 p. 122, t. 4. f. 17. Thallus effuse, very 

 minute, fruticulose, erect, branched, 

 olive-brown, dark-brown or blackish ; 

 branches slender, elongato-papillate, un- 

 equally rounded, somewhat constricted 

 or attenuate at the base. Apothecia 

 very minute, scattered, concave, pale 

 brown or brownish-red, the margin 

 smooth, entire ; spores ovoid or oblong, 

 3-5-septate, and murali-locular, 0,022 

 27 mm. long, 0,009-14 mm. thick. 

 Cromb. Journ. Bot. 1874, p. 336 ; 

 Leight. Lich. Fl. Suppl. p. 468, ed. 3, 

 p. 34. Brit. Exs. : Cromb. n. 7. 



In its earlier stages of growth this has 

 the appearance of a Sirosophon. The thal- 

 lus is cellular, and the gonimia are often 

 3-moniliform. Though resembling a mi- 

 nute state of L. lvph(eum, it is distin- 

 guished by its peculiar habit and the 



Fig. 17. 



form of the spores It js very rarely Leptogium miwosc'opmim Nyl. 

 fertile. On the thallus is occasionally . Thallus, x 30. i. Sec- 



seen a parasitic Obryzum described here-' 

 after. 



tion of apothecium, x30. 

 c. Three spores, xoOO. 

 Hal. On slaty rocks, but chiefly on chalk pebbles and calcareous walls, 



F2 



