494 125. Pyrenula, 5. IDIOTHALAME, PI. cell. aph. 
3. Pyrenula nigrescens. Blackish nut-moss. 
Crust tartarlike, slightly cracked, uneven, brownish- 
black; apothecia enlarged at bottom, depressed, rather 
wrinkled, closed, strictly surrounding the greatest part of 
the prominent, nipplelike thalamium. 
Lichen umbrinus, Achar. Prod. 14; Engl. Bot. 1499. 
Verrucaria umbrina, Achar. Meth, 122. 
Verrucaria antiquitatis, Florke in Berl, Mag. 1807, 1, 17. 
Pyrenula nigrescens, Achar. Syn, 126. 
On stones. 
V. 126. THELOTREMA. Acharius. Open-wart-moss. 
Thallus crustlike, cartilaginous, flat, expanded, adnate, 
uniform ; apothecia wartshape, formed of the thallus, open, 
bordered; thalamium single, enclosed in the wart; peri- 
thecia double; one halved above, thick, black, seldom want- 
ing; the other very thin, membranaceous, sometimes alone, 
or broken above; surrounding a compressed, cellular, 
slightly streaked nucleus, placed in the bottom of the wart. 
1. Thelotrema lepadinum. Barnacle open-wart-moss. - 
Crust smooth, whitish; apothecta smooth, nearly conoid, 
edge of the opening thin, simple, rather bent inwards, con- 
tracted; bottom covered with a membrane which becomes 
torn. 
Lichen inclusus, Engl. Bot. 678. 
Lichen lepadinus, Achar. Pred. 30. 
Thelotrema lepadinum, Achar. Meth. 132; Lich. 312. 
On the bark of trees. 
2. Thel. exanthematicum. Eruptive open-wart-moss. 
Crust rather tartarlike, thin, not cracked, greyish: apo- 
thecia convex, half sunk, whiter; opening half closed, 
radiately cracked, becomes gaping; bottom veiled, yellow- 
ish flesh-colour. 
Lichen volvatus, Villars Delph. 55. 
Lichen exanthematicus, Smith in Lin. Tr.1,81; Engl. Bot. 1184. 
Urceolaria exanthematica, Achar. Meth. 146. 
Thelotrema exanthematica, Achar. Lich. 313. 
On rocks, especially limestone. : 
Halit peculiar, but seems most referable to this genus. 
3. Thelotrema.ageleum. Inelegant open-wart-moss. 
Crust white, rather powdery, or sprinkled with very 
small granules or soredia; apothecia pressed close, few; 
slightly sunk in the crust. 
