BRITISH LICHENS

364 PYRENOCARPElE MICROTHELIA
The specimens in the British Museum were collected by W. Joshua
and labelled by him A. saxicola var.
Hab. On calcareous rocks.-B. M. Sapperton, GIoucestershire.
Form octospora Wats. in Journ. Bot. lxiii. (1925).-Similar
to the species, but with 8 spores in the ascus.
Hab. On calcareous rocks, Cheltenham (H. H. Knight).
4. M. exerrans A. L. Sm.-Thallus thin, blackish, scattered.
Perithecia minute, black; perithecial waH entire; spores 8 in the
ascus, blackish, oblong, I-septate, 10-15 {L long, 3-5 {L thick;
hymenial gelatine wine-red with iodme.-Endococcus exerrans
Ny!. in Flora lxii. 360 (1879); Cromb. in GreviHea viii. 114 (1880).
Distinguished by the narrow spores. Nylander notes the rather
thick colourless chroolepoid gonidia with cells 18-23 [1. thick.
Hab. On quartzose stones.-B. M. Ben-y-GIoe, Blair Athole,
Pcrthshire.
5. M. dissepta A. L. Sm.-Thallus whitish-grey, sometimes
faintly yellowish, tartareous, thm, slightly cracked-areolate, subdeterminate
(probably not proper). Perithecia black, numerous,
somewhat prominent, the upper part convex, the ostiole a minute
pore; perithecial wall entire, paraphyses indistinct; spores 8 in
the ascus, eUipsoid, brown, 3-septate, 18-22 {Llong, 7-10 [1. thick;
hymenial gelatine not tinged with iodine.-Verrucaria dissepta
NyI. in Flora lix. 576 (1876); Cromb. in Grevil1ea v. 107 (1877);
Leight. Lich. FI. ed. 3, 480.
Nylander (l. c.) suggests that possibly the perithecia may be
parasitic on the thallus of some other lichen. The specimen from
Achill lsI. is on Rhizocarpon conJervotdes.
lIab. On mica-schist rocks.-Dis!r. W. Ireland.-B. M. Dooega
Road, Achill lsI., Mayo.
121. PORINA Ach. Lich. Dniv. 60 (1810) pro parte, emend.
MueH. Arg. in Flora lxvi. 320 (1883).-Segestrella Fr. Lich. Eur.
460 (1831) (Segestria tom. Cit. 429); Mudd Man. 283. (PI. 55.)
Thallus variously crustaceous, not corticated, sometimes
developed within the substratum. Peri the cia simple, superficial
or semi-immersed; perithecial wall light-coloured, becoming
darker towards the ostiole, entirely dark-coloured, entire or
dimidiate; paraphyses persistent, sImple; asci elongate, 6--8spored;
spores elongate-fusiform or clavate, colourless, 2- to multiseptate,
rarely wIth longItudinal septa. Spermogones small,
globose wIth simple or branched sterigmata and rod-hke or
elongate-fusiform spermatia.
Distinguished from Arlhopyrenia by the character of the paraphyses
and spores. The texture of the peritheClal wall is also more
variable; it is usually softer iu texture, and in some species waxy and
light-coloured (Segestrella).